The pollen beetle, Brassicogethes viridescens, also known as the bronzed blossom pollen beetle can be a serious pest of canola. It is native to Europe and is an invasive species in Canada. Pollen beetle is now established in Quebec, Prince Edward Island, and Nova Scotia in eastern Canada. Thus far, pollen beetle has not been detected in the prairie provinces of Alberta, Saskatchewan, or Manitoba.
Adult pollen beetles are quite small, only about 2.5 mm, but can disperse up to 3 km to find host plants. Hosts include canola, mustard, and a variety of cruciferous weeds. In the spring, pollen beetles emerge from overwintering sites and disperse to their host crops. Female pollen beetles lay eggs in buds and larvae develop inside the buds. Larvae can be about 4 mm long when they are ready to pupate, have black heads, and have black spots on each segment of their abdomen. Larvae pupate in the soil and new generation adults emerge in late summer. The adult stage overwinters.
Pollen beetle feeding damage on canola buds. Photographed by Olivia Dorn, AAFC-Charlottetown.
Both adult and larval stages of the pollen beetle can cause damage to canola and other host plants. Adult pollen beetles feed on developing buds, flower parts, and pollen. Adults may also consume the pollen of non-host crops, especially in the spring and late summer. Larvae consume pollen, both from developing buds and from open flowers. Larval damage can significantly reduce seed production.
For more information (and pictures), please check out the pollen beetle pages in Field Crop and Forage Pests and their Natural Enemies in Western Canada available in English and French.
There is one generation of cabbage seedpod weevil (CSPW; Ceutorhynchus obstrictus) per year. The overwintered adult is an ash-grey weevil measuring 3-4mm long (Fig. 1; left photo). Mating and oviposition are quickly followed by eggs hatching within developing canola pods (Fig. 1; right photo). The highly concealed larvae feed within the pod, consuming the developing seeds.
Figure 1. Cabbage seedpod weevil (left) and egg dissected from within a canola pod (right). Photos: the late Dr. Lloyd Dosdall.
Damage: Adult feeding damage to buds is more evident in dry years when canola is unable to compensate for bud loss. Adults mate following a pollen meal then the female will deposit a single egg through the wall of a developing pod or adjacent to a developing seed within the pod (Fig. 1; right photo). Eggs are oval and an opaque white, each measuring ~1mm long. Typically, a single egg is laid per pod although, when CSPW densities are high, two or more eggs may be laid per pod.
There are four larval instar stages of the CSPW and each stage is white and grub-like in appearance ranging up to 5-6mm in length (Fig. 2; left photo). The first instar larva feeds on the cuticle on the outside of the pod while the second instar larva bores into the pod (Fig. 2; right photo, lower pod), feeding on the developing seeds. A single larva consumes about 5 canola seeds. The mature larva chews a small, circular exit hole (Fig. 2; right photo, upper pod) from which it drops to the soil surface and pupation takes place in the soil within an earthen cell. Approximately 10 days later, the new adult emerges to feed on maturing canola pods. Later in the season, these new adults migrate to overwintering sites beyond the field.
Figure 2. Larva feeding amongst developing seeds within canola pod (left) and larval entrance hole (right photo, lower pod) compared to mature larval exit hole (right photo, uppower pod). Photos: the late Dr. Lloyd Dosdall.
Prairie-Wide Monitoring: The annual cabbage seedpod weevil survey is performed in canola at early flower stages using sweep-net collections. Review the prairie-wide historical survey maps for this insect species. Review the PPMN monitoring protocol although the provinces of Alberta, Saskatchewan, and Manitoba have specific survey protocols for their respective network cooperators. Commercial fields where comparatively higher densities of adult cabbage seedpod weevils were observed in 2024 are highlighted yellow, orange, or red in the geospatial map featured in Figure 3.Areas where historically higher densities of cabbage seedpod weevil were observed in 2024 are worth prioritizing in 2025.
Figure 3. Densities of cabbage seedpod weevil (Ceutorhynchus obstrictus) observed in sweep-net samples retrieved from commercial fields of canola (Brassica napus) grown in Manitoba, Saskatchewan, Alberta, and the British Columbia portion of the Peace River region in 2024.
In-Field Monitoring:
Begin sampling when the crop first enters the bud stage and continue through the flowering.
Sweep-net samples should be taken at ten locations within the field with ten 180° sweeps per location.
Count the number of weevils at each location. Samples should be taken in the field perimeter as well as throughout the field.
Adults will invade fields from the margins and if infestations are high in the borders, application of an insecticide to the field margins may be effective in reducing the population to levels below which economic injury will occur.
An insecticide application is recommended when three to four weevils per sweep are collected and has been shown to be the most effective when canola is in the 10 to 20% bloom stage (2-4 days after flowering starts).
Consider making insecticide applications late in the day to reduce the impact on pollinators. Whenever possible, provide advanced warning of intended insecticide applications to commercial beekeepers operating in the vicinity to help protect foraging pollinators.
High numbers of adults in the fall may indicate the potential for economic infestations the following spring.
Albertan growers can report field observations and check the live map for CSPW posted by Alberta Agriculture and Irrigation (screenshot provided below as an example; retrieved 2025Jun19 but will be updated with 2025 reports as the season progresses).
Aphid populations can quickly increase at this point in the season and particularly when growing conditions are warm and dry. Access the Provincial Insect Pest Report for Wk15 to remain alert to areas and crops suffering from aphid pest pressure.
Figure 1. Pea aphid adults (each 3-4 mm long) and nymph. Photo: M. Dolinski.
Additionally, several aphid pest species are described in the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) which is accessible as a free downloadable PDF in either English or French on our Field Guides page. PDF copies of the individual pages have been linked below to access quickly: • Corn leaf aphid or Rhopalosiphum maidis (Fitch) • English grain aphid or Sitobion (Macrosiphum) avenae (Fabricius) • Oat-birdcherry aphid or Rhopalosiphum padi (Linnaeus) • Pea aphid or Acyrthosiphon pisum (Harris) • Potato aphid or Macrosiphum euphorbiae (Thomas) • Soybean aphid or Aphis glycines (Matsumura) • Turnip aphid or Lipaphis erysimi (Kaltenbach) • Sugar beet root aphid or Pemphigus betae Doane • Russian wheat aphid or Diuraphis noxia (Mordvilko)
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring, adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Spring Pheromone Trap Monitoring of Adult Males: Across the Canadian prairies, spring monitoring is initiated to acquire weekly counts of adult moths (Fig. 1) attracted to pheromone-baited delta traps deployed in fields. Weekly trap interceptions are observed to generate cumulative counts. These cumulative count estimates are broadly categorized to help producers prioritize and time in-field scouting for larvae.
Figure 1. Adult diamondback moth.
Diamondback moths were captured on pheromone traps across western Canada from mid- to late-May in 2025. Once adults arrive, there can be several in-season, non-migrant generations of diamondback moth developing throughout the remainder of the growing season. Warm, dry weather tends to promote rapid development of high-density populations of larvae capable of causing severe damage to host crops, including canola.
As of June 29, 2025, model outputs suggest that diamondback moth populations are primarily in the first non-migrant generation but the second generation may be emerging in areas around Winnipeg and east of Lethbridge (Fig. 2).
Figure 2. Predicted number of in-season generations of diamondback moth (Plutella xylostella) expected to have developed across the Canadian prairies, as of June 29, 2025.
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2025.
In-Field Monitoring:Remove plants in an area measuring 0.1 m² (about 12″ square), beat them onto a clean surface and count the number of larvae (Fig. 3) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
Figure 3. Diamondback larva measuring ~8mm long. Note brown head capsule and forked appearance of prolegs on posterior.
The economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1 m² (approximately 2-3 larvae per plant). Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1 m² (approximately 1-2 larvae per plant).
Figure 4. Diamondback moth pupa within silken cocoon.
The phenology model for bertha armyworm development on the Canadian prairies was developed by Ross Weiss and Owen Olfert. Model simulations were used to estimate development of bertha armyworm as of June 20, 2025.
The model outputs show bertha armyworm populations, where present, should consist mainly of either eggs and larvae (Fig. 1). Populations across the in the majority of Prairie growing region should mainly be in the egg stage. Larvae should be present in areas south of Winnipeg and between Lethbridge and Swift Current (Fig. 2).
Figure 1. The proportion of the (Mamestra configurata) population that is predicted to be in the EGG stage (% of total population) across the Canadian prairies as of June 29, 2025.Figure 2. The proportion of the (Mamestra configurata) population that is predicted to be in the LARVAL stage (% of total population) across the Canadian prairies as of June 29, 2025.
Figure 3 includes photos of the various life stages of the bertha armyworm. There is one generation per year and pupae overwinter in the soil (Fig. 3, C). Each growing season, green unitraps utilizing pheromone lures are deployed and checked weekly over a 6-week window. Cumulative counts generated from the pheromone traps are used to estimate subsequent bertha armyworm densities. The cumulative moth count data is compiled using geospatial maps then posted to support and time in-field scouting for damaging populations of larvae by mid-July through to August.
Figure 3. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2025. For example, Manitoba Agriculture’s June 19th Crop Pest Report includes Figure 4 with a reminder that other moth species are actively flying now so examine wing colourations and patterning carefully when checking the contents of bertha armyworm pheromone traps! Clover cutworm can be common by-catch in pheromone traps designed to monitor bertha armyworm, but also those designed to monitor true armyworm.
Figure 4. Comparison of diagnostic wing features of three moth species. Images and information all courtesy of Manitoba Agriculture, J. Gavloski who originally included in the June 19, 2025, issue of the Manitoba Crop Pest Update.
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018), accessible as a free downloadable PDF in either English or French on our Field Guides page. Also consider reviewing this 2019 Insect of the Week featuring bertha armyworm and its doppelganger, the clover cutworm!
Lygus bugs are polyphagous (i.e., feed on plants belonging to several Families of plants) and multivoltine (i.e., capable of producing multiple generations per year). Both the adult (Fig. 1) and five nymphal instar stages (Fig. 2) are a sucking insect that focuses feeding activities on developing buds, pods and seeds. Adults overwinter in northern climates. The economic threshold for Lygus in canola is applied at late flower and early pod stages.
Recent research in Alberta has resulted in a revision to the thresholds recommended for the management of Lygus in canola. Under ideal growing conditions (i.e., ample moisture) a threshold of 20-30 lygus per 10 sweeps is recommended. Under dry conditions, a lower threshold may be used, however, because drought limits yield potential in canola, growers should be cautious if considering the use of foliar-applied insecticide at lygus densities below the established threshold of 20-30 per 10 sweeps.In drought-affected fields that still support near-average yield potential, a lower threshold of ~20 lygus per 10 sweeps may be appropriate for stressed canola. Even if the current value of canola remains high (e.g., >$19.00 per bu), control at densities of <10 lygus per 10 sweeps is not likely to be economical. Research indicates that lygus numbers below 10 per 10 sweeps (one per sweep) can on occasion increase yield in good growing conditions – likely through plant compensation for a small amount of feeding stress.
Figure 1. Adult Lygus lineolaris (5-6 mm long) (photo: AAFC-Saskatoon).
Figure 2. Fifth instar lygus bug nymph (3-4 mm long) (photo: AAFC-Saskatoon).
Damage: Lygus bugs have piercing-sucking mouthparts and physically damage the plant by puncturing the tissue and sucking plant juices. The plants also react to the toxic saliva that the insects inject when they feed. Lygus bug infestations can cause alfalfa to have short stem internodes, excessive branching, and small, distorted leaves. In canola, lygus bugs feed on buds and blossoms and cause them to drop. They also puncture seed pods and feed on the developing seeds causing them to turn brown and shrivel.
Scouting tips to keep in mind: Begin monitoring canola when it bolts and continues until seeds within the pods are firm. Since adults can move into canola from alfalfa, check lygus bug numbers in canola when nearby alfalfa crops are cut.
Sample the crop for lygus bugs on a sunny day when the temperature is above 20 °C and the crop canopy is dry. With a standard insect net (38 cm diameter), take ten 180 ° sweeps. Count the number of lygus bugs in the net. Sampling becomes more representative IF repeated at multiple spots within a field so sweep in at least 10 locations within a field to estimate the density of lygus bugs.
Biological and monitoring information related to Lygus in field crops is posted by the provinces of Manitoba or Alberta fact sheets or the Prairie Pest Monitoring Network’s monitoring protocol. Also refer to the Lygus pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page. The Canola Council of Canada’s “Canola Encyclopedia” also summarizes Lygus bugs. The Flax Council of Canada includes Lygus bugs in their Insect Pest downloadable PDF chapter plus the Saskatchewan Pulse Growers summarize Lygus bugs in faba beans.
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring, adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Spring Pheromone Trap Monitoring of Adult Males: Across the Canadian prairies, spring monitoring is initiated to acquire weekly counts of adult moths (Fig. 1) attracted to pheromone-baited delta traps deployed in fields. Weekly trap interceptions are observed to generate cumulative counts. These cumulative count estimates are broadly categorized to help producers prioritize and time in-field scouting for larvae.
Figure 1. Adult diamondback moth.
Diamondback moths were captured on pheromone traps across western Canada from mid- to late-May in 2025. Once adults arrive, there can be several in-season, non-migrant generations of diamondback moth developing throughout the remainder of the growing season. Warm, dry weather tends to promote rapid development of high-density populations of larvae capable of causing severe damage to host crops, including canola.
As of June 22, 2025, model outputs predict that diamondback moth populations are in the first non-migrant generation (Fig. 2).
Figure 2. Predicted number of in-season generations of diamondback moth (Plutella xylostella) expected to have developed across the Canadian prairies, as of June 22, 2025.
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2025.
In-Field Monitoring:Remove plants in an area measuring 0.1 m² (about 12″ square), beat them onto a clean surface and count the number of larvae (Fig. 3) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
Figure 3. Diamondback larva measuring ~8mm long. Note brown head capsule and forked appearance of prolegs on posterior.
The economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1 m² (approximately 2-3 larvae per plant). Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1 m² (approximately 1-2 larvae per plant).
Figure 4. Diamondback moth pupa within silken cocoon.
The phenology model for bertha armyworm development on the Canadian prairies was developed by Ross Weiss and Owen Olfert. Model simulations were used to estimate development of bertha armyworm as of June 22, 2025.
The model outputs predict that bertha armyworm populations, where present, should consist mainly of adults laying eggs (Fig. 1). Based on the model outputs, populations throughout most of Alberta and Saskatchewan are predicted to be mainly be in the egg stage (as of June 22, 2025). In some areas south of Winnipeg, east of Lethbridge, and northeast of Swift Current, larvae may be present (Fig. 2).
Figure 1. The proportion of the (Mamestra configurata) population that is predicted to be in the EGG stage (% of total population) across the Canadian prairies as of June 22, 2025.Figure 2. The proportion of the (Mamestra configurata) population that is predicted to be in the LARVAL stage (% of total population) across the Canadian prairies as of June 22, 2025.
Figure 3 includes photos of the various life stages of the bertha armyworm. There is one generation per year and pupae overwinter in the soil (Fig. 3, C). Each growing season, green unitraps utilizing pheromone lures are deployed and checked weekly over a 6-week window. Cumulative counts generated from the pheromone traps are used to estimate subsequent bertha armyworm densities. The cumulative moth count data is compiled using geospatial maps then posted to support and time in-field scouting for damaging populations of larvae by mid-July through to August.
Figure 3. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2025. For example, Manitoba Agriculture’s June 19th Crop Pest Report includes Figure 4 with a reminder that other moth species are actively flying now so examine wing colourations and patterning carefully when checking the contents of bertha armyworm pheromone traps! Clover cutworm can be common by-catch in pheromone traps designed to monitor bertha armyworm, but also those designed to monitor true armyworm.
Figure 4. Comparison of diagnostic wing features of three moth species. Images and information all courtesy of Manitoba Agriculture, J. Gavloski who originally included in the June 19, 2025, issue of the Manitoba Crop Pest Update.
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018), accessible as a free downloadable PDF in either English or French on our Field Guides page. Also consider reviewing this 2019 Insect of the Week featuring bertha armyworm and its doppelganger, the clover cutworm!
The phenology model for bertha armyworm development on the Canadian prairies was developed by Ross Weiss and Owen Olfert. Model simulations were used to estimate development of bertha armyworm as of June 15, 2025.
The model indicates that in areas where bertha armyworm populations are present, the population should consist mainly of adults (Fig. 1). Based on the model readings, the percentage of adult berth armyworm in the population should be highest in Alberta and Saskatchewan. In some areas south of Winnipeg, east of Lethbridge, and northeast of Swift Current, the model predicts that female moths are already laying eggs (Fig. 2).
Figure 1. The proportion of the (Mamestra configurata) population that is predicted to be in the adult stage (% of total population) across the Canadian prairies as of June 15, 2025.Figure 2. The proportion of the (Mamestra configurata) population that is predicted to be in the egg stage (% of total population) across the Canadian prairies as of June 15, 2025.
Figure 3 includes photos of the various life stages of the bertha armyworm. There is one generation per year and pupae overwinter in the soil (Fig. 3, C). Each growing season, green unitraps utilizing pheromone lures are deployed and checked weekly over a 6-week window. Cumulative counts generated from the pheromone traps are used to estimate subsequent bertha armyworm densities. The cumulative moth count data is compiled using geospatial maps then posted to support and time in-field scouting for damaging populations of larvae by mid-July through to August.
Figure 3. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2025. For example, Manitoba Agriculture’s June 19th Crop Pest Report includes Figure 4 with a reminder that other moth species are actively flying now so examine wing colourations and patterning carefully when checking the contents of bertha armyworm pheromone traps! Clover cutworm can be common by-catch in pheromone traps designed to monitor bertha armyworm, but also those designed to monitor true armyworm.
Figure 4. Comparison of diagnostic wing features of three moth species. Images and information all courtesy of Manitoba Agriculture, J. Gavloski who originally included in the June 19, 2025, issue of the Manitoba Crop Pest Update.
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018), accessible as a free downloadable PDF in either English or French on our new Field Guides page. Also consider reviewing this 2019 Insect of the Week featuring bertha armyworm and its doppelganger, the clover cutworm!
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring, adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Spring Pheromone Trap Monitoring of Adult Males: Across the Canadian prairies, spring monitoring is initiated to acquire weekly counts of adult moths (Fig. 1) attracted to pheromone-baited delta traps deployed in fields. Weekly trap interceptions are observed to generate cumulative counts. These cumulative count estimates are broadly categorized to help producers prioritize and time in-field scouting for larvae.
Figure 1. Adult diamondback moth.
In-Field Monitoring:Remove plants in an area measuring 0.1 m² (about 12″ square), beat them onto a clean surface and count the number of larvae (Fig. 2) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
Figure 2. Diamondback larva measuring ~8mm long. Note brown head capsule and forked appearance of prolegs on posterior.
The economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1 m² (approximately 2-3 larvae per plant). Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1 m² (approximately 1-2 larvae per plant).
Figure 3. Diamondback moth pupa within silken cocoon.
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2025.
There is one generation of cabbage seedpod weevil (CSPW; Ceutorhynchus obstrictus) per year. The overwintered adult is an ash-grey weevil measuring 3-4mm long (Fig. 1; left photo). Mating and oviposition are quickly followed by eggs hatching within developing canola pods (Fig. 1; right photo). The highly concealed larvae feed within the pod, consuming the developing seeds.
Figure 1. Cabbage seedpod weevil (left) and egg dissected from within a canola pod (right). Photos: the late Dr. Lloyd Dosdall.
Damage: Adult feeding damage to buds is more evident in dry years when canola is unable to compensate for bud loss. Adults mate following a pollen meal then the female will deposit a single egg through the wall of a developing pod or adjacent to a developing seed within the pod (Fig. 1; right photo). Eggs are oval and an opaque white, each measuring ~1mm long. Typically, a single egg is laid per pod although, when CSPW densities are high, two or more eggs may be laid per pod.
There are four larval instar stages of the CSPW and each stage is white and grub-like in appearance ranging up to 5-6mm in length (Fig. 2; left photo). The first instar larva feeds on the cuticle on the outside of the pod while the second instar larva bores into the pod (Fig. 2; right photo, lower pod), feeding on the developing seeds. A single larva consumes about 5 canola seeds. The mature larva chews a small, circular exit hole (Fig. 2; right photo, upper pod) from which it drops to the soil surface and pupation takes place in the soil within an earthen cell. Approximately 10 days later, the new adult emerges to feed on maturing canola pods. Later in the season, these new adults migrate to overwintering sites beyond the field.
Figure 2. Larva feeding amongst developing seeds within canola pod (left) and larval entrance hole (right photo, lower pod) compared to mature larval exit hole (right photo, uppower pod). Photos: the late Dr. Lloyd Dosdall.
Prairie-Wide Monitoring: The annual cabbage seedpod weevil survey is performed in canola at early flower stages using sweep-net collections. Review the prairie-wide historical survey maps for this insect species. Review the PPMN monitoring protocol although the provinces of Alberta, Saskatchewan, and Manitoba have specific survey protocols for their respective network cooperators. Commercial fields where comparatively higher densities of adult cabbage seedpod weevils were observed in 2024 are highlighted yellow, orange, or red in the geospatial map featured in Figure 3.Areas where historically higher densities of cabbage seedpod weevil were observed in 2024 are worth prioritizing in 2025.
Figure 3. Densities of cabbage seedpod weevil (Ceutorhynchus obstrictus) observed in sweep-net samples retrieved from commercial fields of canola (Brassica napus) grown in Manitoba, Saskatchewan, Alberta, and the British Columbia portion of the Peace River region in 2024.
In-Field Monitoring:
Begin sampling when the crop first enters the bud stage and continue through the flowering.
Sweep-net samples should be taken at ten locations within the field with ten 180° sweeps per location.
Count the number of weevils at each location. Samples should be taken in the field perimeter as well as throughout the field.
Adults will invade fields from the margins and if infestations are high in the borders, application of an insecticide to the field margins may be effective in reducing the population to levels below which economic injury will occur.
An insecticide application is recommended when three to four weevils per sweep are collected and has been shown to be the most effective when canola is in the 10 to 20% bloom stage (2-4 days after flowering starts).
Consider making insecticide applications late in the day to reduce the impact on pollinators. Whenever possible, provide advanced warning of intended insecticide applications to commercial beekeepers operating in the vicinity to help protect foraging pollinators.
High numbers of adults in the fall may indicate the potential for economic infestations the following spring.
Albertan growers can report field observations and check the live map for CSPW posted by Alberta Agriculture and Irrigation (screenshot provided below as an example; retrieved 2025Jun19 but will be updated with 2025 reports as the season progresses).
Lygus bugs are polyphagous (i.e., feed on plants belonging to several Families of plants) and multivoltine (i.e., capable of producing multiple generations per year). Both the adult (Fig. 1) and five nymphal instar stages (Fig. 2) are a sucking insect that focuses feeding activities on developing buds, pods and seeds. Adults overwinter in northern climates. The economic threshold for Lygus in canola is applied at late flower and early pod stages.
Recent research in Alberta has resulted in a revision to the thresholds recommended for the management of Lygus in canola. Under ideal growing conditions (i.e., ample moisture) a threshold of 20-30 lygus per 10 sweeps is recommended. Under dry conditions, a lower threshold may be used, however, because drought limits yield potential in canola, growers should be cautious if considering the use of foliar-applied insecticide at lygus densities below the established threshold of 20-30 per 10 sweeps.In drought-affected fields that still support near-average yield potential, a lower threshold of ~20 lygus per 10 sweeps may be appropriate for stressed canola. Even if the current value of canola remains high (e.g., >$19.00 per bu), control at densities of <10 lygus per 10 sweeps is not likely to be economical. Research indicates that lygus numbers below 10 per 10 sweeps (one per sweep) can on occasion increase yield in good growing conditions – likely through plant compensation for a small amount of feeding stress.
Figure 1. Adult Lygus lineolaris (5-6 mm long) (photo: AAFC-Saskatoon).
Figure 2. Fifth instar lygus bug nymph (3-4 mm long) (photo: AAFC-Saskatoon).
Damage: Lygus bugs have piercing-sucking mouthparts and physically damage the plant by puncturing the tissue and sucking plant juices. The plants also react to the toxic saliva that the insects inject when they feed. Lygus bug infestations can cause alfalfa to have short stem internodes, excessive branching, and small, distorted leaves. In canola, lygus bugs feed on buds and blossoms and cause them to drop. They also puncture seed pods and feed on the developing seeds causing them to turn brown and shrivel.
Scouting tips to keep in mind: Begin monitoring canola when it bolts and continues until seeds within the pods are firm. Since adults can move into canola from alfalfa, check lygus bug numbers in canola when nearby alfalfa crops are cut.
Sample the crop for lygus bugs on a sunny day when the temperature is above 20 °C and the crop canopy is dry. With a standard insect net (38 cm diameter), take ten 180 ° sweeps. Count the number of lygus bugs in the net. Sampling becomes more representative IF repeated at multiple spots within a field so sweep in at least 10 locations within a field to estimate the density of lygus bugs.
Biological and monitoring information related to Lygus in field crops is posted by the provinces of Manitoba or Alberta fact sheets or the Prairie Pest Monitoring Network’s monitoring protocol. Also refer to the Lygus pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page. The Canola Council of Canada’s “Canola Encyclopedia” also summarizes Lygus bugs. The Flax Council of Canada includes Lygus bugs in their Insect Pest downloadable PDF chapter plus the Saskatchewan Pulse Growers summarize Lygus bugs in faba beans.
The phenology model for bertha armyworm development on the Canadian prairies was developed by Ross Weiss and Owen Olfert. Model simulations were used to estimate development of bertha armyworm as of June 8, 2025. Model outputs predict that the adult flight has likely started in most areas where bertha armyworm populations are present except for in parts of the BC Peace River region and along the foothills in western Alberta where the percentage of the population in the adult stage is estimated to be less than 15 % (Fig. 1). Based on the model readings, the percentage of bertha armyworm in the adult stage, where populations are present, should be highest in areas between Edmonton and Calgary in Alberta.
Figure 1. The proportion of the (Mamestra configurata) population that is predicted to be in the adult stage (% of total population) across the Canadian prairies as of June 8, 2025.
Figure 2 includes photos of the various life stages of the bertha armyworm. There is one generation per year and pupae overwinter in the soil (Fig. 2, C). Each growing season, green unitraps utilizing pheromone lures are deployed and checked weekly over a 6-week window. Cumulative counts generated from the pheromone traps are used to estimate subsequent bertha armyworm densities. The cumulative moth count data is compiled using geospatial maps then posted to support and time in-field scouting for damaging populations of larvae by mid-July through to August.
Figure 2. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018), accessible as a free downloadable PDF in either English or French on our new Field Guides page. Also consider reviewing the 2019 Insect of the Week, which featured bertha armyworm and its doppelganger, the clover cutworm!
There is one generation of cabbage seedpod weevil (CSPW; Ceutorhynchus obstrictus) per year. The overwintered adult is an ash-grey weevil measuring 3-4mm long (Fig. 1; left photo). Mating and oviposition are quickly followed by eggs hatching within developing canola pods (Fig. 1; right photo). The highly concealed larvae feed within the pod, consuming the developing seeds.
Figure 1. Cabbage seedpod weevil (left) and egg dissected from within a canola pod (right). Photos: the late Dr. Lloyd Dosdall.
Damage: Adult feeding damage to buds is more evident in dry years when canola is unable to compensate for bud loss. Adults mate following a pollen meal then the female will deposit a single egg through the wall of a developing pod or adjacent to a developing seed within the pod (Fig. 1; right photo). Eggs are oval and an opaque white, each measuring ~1mm long. Typically, a single egg is laid per pod although, when CSPW densities are high, two or more eggs may be laid per pod.
There are four larval instar stages of the CSPW and each stage is white and grub-like in appearance ranging up to 5-6mm in length (Fig. 2; left photo). The first instar larva feeds on the cuticle on the outside of the pod while the second instar larva bores into the pod (Fig. 2; right photo, lower pod), feeding on the developing seeds. A single larva consumes about 5 canola seeds. The mature larva chews a small, circular exit hole (Fig. 2; right photo, upper pod) from which it drops to the soil surface and pupation takes place in the soil within an earthen cell. Approximately 10 days later, the new adult emerges to feed on maturing canola pods. Later in the season, these new adults migrate to overwintering sites beyond the field.
Figure 2. Larva feeding amongst developing seeds within canola pod (left) and larval entrance hole (right photo, lower pod) compared to mature larval exit hole (right photo, uppower pod). Photos: the late Dr. Lloyd Dosdall.
Prairie-Wide Monitoring: The annual cabbage seedpod weevil survey is performed in canola at early flower stages using sweep-net collections. Review the prairie-wide historical survey maps for this insect species. Review the PPMN monitoring protocol although the provinces of Alberta, Saskatchewan, and Manitoba have specific survey protocols for their respective network cooperators. Commercial fields where comparatively higher densities of adult cabbage seedpod weevils were observed in 2024 are highlighted yellow, orange, or red in the geospatial map featured in Figure 3. Areas where historically higher densities of cabbage seedpod weevil were observed in 2024 are worth prioritizing in 2025.
Figure 3. Densities of cabbage seedpod weevil (Ceutorhynchus obstrictus) observed in sweep-net samples retrieved from commercial fields of canola (Brassica napus) grown in Saskatchewan, Alberta, and the British Columbia portion of the Peace River region in 2024.
In-Field Monitoring:
Begin sampling when the crop first enters the bud stage and continue through the flowering.
Sweep-net samples should be taken at ten locations within the field with ten 180° sweeps per location.
Count the number of weevils at each location. Samples should be taken in the field perimeter as well as throughout the field.
Adults will invade fields from the margins and if infestations are high in the borders, application of an insecticide to the field margins may be effective in reducing the population to levels below which economic injury will occur.
An insecticide application is recommended when three to four weevils per sweep are collected and has been shown to be the most effective when canola is in the 10 to 20% bloom stage (2-4 days after flowering starts).
Consider making insecticide applications late in the day to reduce the impact on pollinators. Whenever possible, provide advanced warning of intended insecticide applications to commercial beekeepers operating in the vicinity to help protect foraging pollinators.
High numbers of adults in the fall may indicate the potential for economic infestations the following spring.
Albertan growers can report field observations and check the live map for CSPW posted by Alberta Agriculture and Irrigation (screenshot provided below as an example; retrieved 2022Jul28 but will be updated with 2025 reports as season progresses).
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring, adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Spring Pheromone Trap Monitoring of Adult Males: Across the Canadian prairies, spring monitoring is initiated to acquire weekly counts of adult moths (Fig. 1) attracted to pheromone-baited delta traps deployed in fields. Weekly trap interceptions are observed to generate cumulative counts. These cumulative count estimates are broadly categorized to help producers prioritize and time in-field scouting for larvae.
Figure 1. Adult diamondback moth.
In-Field Monitoring:Remove plants in an area measuring 0.1 m² (about 12″ square), beat them onto a clean surface and count the number of larvae (Fig. 2) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
Figure 2. Diamondback larva measuring ~8mm long. Note brown head capsule and forked appearance of prolegs on posterior.
The economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1 m² (approximately 2-3 larvae per plant). Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1 m² (approximately 1-2 larvae per plant).
Figure 3. Diamondback moth pupa within silken cocoon.
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2025.
There is one generation of cabbage seedpod weevil (CSPW; Ceutorhynchus obstrictus) per year. The overwintered adult is an ash-grey weevil measuring 3-4mm long (Fig. 1; left photo). Mating and oviposition are quickly followed by eggs hatching within developing canola pods (Fig. 1; right photo). The highly concealed larvae feed within the pod, consuming the developing seeds.
Figure 1. Cabbage seedpod weevil (left) and egg dissected from within a canola pod (right). Photos: the late Dr. Lloyd Dosdall.
Damage: Adult feeding damage to buds is more evident in dry years when canola is unable to compensate for bud loss. Adults mate following a pollen meal then the female will deposit a single egg through the wall of a developing pod or adjacent to a developing seed within the pod (Fig. 1; right photo). Eggs are oval and an opaque white, each measuring ~1mm long. Typically, a single egg is laid per pod although, when CSPW densities are high, two or more eggs may be laid per pod.
There are four larval instar stages of the CSPW and each stage is white and grub-like in appearance ranging up to 5-6mm in length (Fig. 2; left photo). The first instar larva feeds on the cuticle on the outside of the pod while the second instar larva bores into the pod (Fig. 2; right photo, lower pod), feeding on the developing seeds. A single larva consumes about 5 canola seeds. The mature larva chews a small, circular exit hole (Fig. 2; right photo, upper pod) from which it drops to the soil surface and pupation takes place in the soil within an earthen cell. Approximately 10 days later, the new adult emerges to feed on maturing canola pods. Later in the season, these new adults migrate to overwintering sites beyond the field.
Figure 2. Larva feeding amongst developing seeds within canola pod (left) and larval entrance hole (right photo, lower pod) compared to mature larval exit hole (right photo, uppower pod). Photos: the late Dr. Lloyd Dosdall.
Prairie-Wide Monitoring: The annual cabbage seedpod weevil survey is performed in canola at early flower stages using sweep-net collections. Review the prairie-wide historical survey maps for this insect species. Review the PPMN monitoring protocol although the provinces of Alberta, Saskatchewan, and Manitoba have specific survey protocols for their respective network cooperators. Commercial fields where comparatively higher densities of adult cabbage seedpod weevils were observed in 2024 are highlighted yellow, orange, or red in the geospatial map featured in Figure 3. Areas where historically higher densities of cabbage seedpod weevil were observed in 2024 are worth prioritizing in 2025.
Figure 3. Densities of cabbage seedpod weevil (Ceutorhynchus obstrictus) observed in sweep-net samples retrieved from commercial fields of canola (Brassica napus) grown in Saskatchewan, Alberta, and the British Columbia portion of the Peace River region in 2024.
In-Field Monitoring:
Begin sampling when the crop first enters the bud stage and continue through the flowering.
Sweep-net samples should be taken at ten locations within the field with ten 180° sweeps per location.
Count the number of weevils at each location. Samples should be taken in the field perimeter as well as throughout the field.
Adults will invade fields from the margins and if infestations are high in the borders, application of an insecticide to the field margins may be effective in reducing the population to levels below which economic injury will occur.
An insecticide application is recommended when three to four weevils per sweep are collected and has been shown to be the most effective when canola is in the 10 to 20% bloom stage (2-4 days after flowering starts).
Consider making insecticide applications late in the day to reduce the impact on pollinators. Whenever possible, provide advanced warning of intended insecticide applications to commercial beekeepers operating in the vicinity to help protect foraging pollinators.
High numbers of adults in the fall may indicate the potential for economic infestations the following spring.
Albertan growers can report field observations and check the live map for CSPW posted by Alberta Agriculture and Irrigation (screenshot provided below as an example; retrieved 2022Jul28 but will be updated with 2025 reports as season progresses).
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring, adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Spring Pheromone Trap Monitoring of Adult Males: Across the Canadian prairies, spring monitoring is initiated to acquire weekly counts of adult moths (Fig. 1) attracted to pheromone-baited delta traps deployed in fields. Weekly trap interceptions are observed to generate cumulative counts. These cumulative count estimates are broadly categorized to help producers prioritize and time in-field scouting for larvae.
Figure 1. Adult diamondback moth.
In-Field Monitoring:Remove plants in an area measuring 0.1 m² (about 12″ square), beat them onto a clean surface and count the number of larvae (Fig. 2) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
Figure 2. Diamondback larva measuring ~8mm long. Note brown head capsule and forked appearance of prolegs on posterior.
The economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1 m² (approximately 2-3 larvae per plant). Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1 m² (approximately 1-2 larvae per plant).
Figure 3. Diamondback moth pupa within silken cocoon.
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2025.
Degree-days can be used to predict the timing of insect development and plan for pest scouting and management. Degree-days are calculated for different insect species using temperature thresholds specific to their development. Based on research, the temperature threshold for bertha armyworm (Mamestra configurata) development is 7 °C and 352 accumulated degree-days (base 7 °C) are required for overwintered pupae to begin their spring development phase. As of May 25, there are no areas on the prairies that have surpassed the degree-day requirement for pupal development of bertha armyworm (Fig. 1).
Figure 1. Growing degree-day heat units (Base 7 °C) accumulated across the Canadian prairies from April 1 to May 25, 2025.
Pheromone traps used to monitor bertha armyworm are typically set up along canola fields when pupal development reaches 75-80%; the 2024 monitoring season started the week of June 10, 2024. Cumulative counts from sentinel pheromone monitoring sites targeting bertha armyworm moths across the Canadian prairies in 2024 are highlighted as geospatial areas where producers are encouraged to prioritize in-field monitoring in 2025. Areas in Figure 2 highlighted yellow, orange, or especially red hosted pheromone traps that intercepted relatively high cumulative counts of moths in 2024 and should be prioritized for in-field scouting in 2025. Review the prairie-wide historical survey maps for this insect species.
Figure 2. Cumulative weekly counts of Bertha armyworm (Mamestra configurata) moths arising from the 2024 growing season.
Figure 3 includes photos of the various life stages of the bertha armyworm. There is one generation per year and pupae overwinter in the soil (Fig. 3, C). Each growing season, green unitraps utilizing pheromone lures are deployed and checked weekly over a 6-week window. Cumlative counts generated from the pheromone traps are used to estimate subsequent bertha armyworm densities. The cumulative moth count data is compiled using geospatial maps then posted to support and time in-field scouting for damaging populations of larvae by mid-July through to August.
Figure 3. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018), accessible as a free downloadable PDF in either English or French on our new Field Guides page. Also consider reviewing the 2019 Insect of the Week, which featured bertha armyworm and its doppelganger, the clover cutworm!
Swede midge, Contarinia nasturtii, is an invasive species in Canada and the United States. Swede midge has been detected by the CFIA in Saskatchewan and Manitoba, but is NOT ESTABLISHED IN THE PRAIRIE REGION and has not been detected in pheromone traps used for monitoring since the CFIA detections in 2007/2008. Swede midge has been found in New Brunswick, Nova Scotia, Prince Edward Island, Ontario, and Quebec. It is well-established in Ontario and Quebec, where it has been extremely damaging to brassica vegetable crops (cabbage, broccoli, kale, cauliflower, etc.) and canola crops.
A canola raceme with flower buds damaged by feeding swede midge larvae. Photographed by Jonathon Williams, AAFC-Saskatoon.
Swede Midge Identification and Life History: Adult swede midge are small, grey or brown coloured flies, about 2 mm long. Adults lay eggs on the growing points of their brassicaceous host plants and larval development prevents normal plant development.
An adult swede midge and translucent swede midge larvae on a growing point of a canola plant. Photographed by Jonathon Williams, AAFC-Saskatoon.
Larvae are 2-4 mm long and yellow-coloured when ready to pupate; early instar larvae are smaller and are often translucent. Once larval development is complete, larvae drop to the soil to pupate. There can be multiple generations per growing season. Swede midge can also remain in the pupal stage in the soil for over a year if soil and temperature conditions are not suitable for adult emergence.
A canola plant from a lab-reared colony of swede midge where the growing points infested with large numbers of swede midge larvae that are nearly ready to pupate. Photographed by Meghan Vankosky, AAFC-Saskatoon.
Swede Midge Monitoring: Pheromone-baited traps are used to monitor for swede midge in Manitoba, Saskatchewan, Alberta, and the Peace River Region of BC. This monitoring program is primarily in place as an early detection system. So far, no swede midge have been caught in pheromone traps set up in the prairie provinces. Results from the 2024 monitoring season are shown below.
As swede midge are moving westward in the United States, it is important to keep monitoring for swede midge in an effort to protect the prairie canola and vegetable industries from this potentially devastating pest.
For more information about swede midge visit:
The swede midge page in Field Crop and Forage Pests and Their Natural Enemies in Western Canada (English or French)
Flea Beetles (Chrysomelidae: Phyllotreta species) – Be on the lookout for flea beetle damage resulting from feeding on canola cotyledons but also on the stem. Two species, Phyllotreta striolata and P. cruciferae, will feed on all cruciferous plants but they can cause economic levels of damage in canola during the seedling stages.
Figure 1. Flea beetle feeding inflicted by overwintered adults including ‘shot-hole’ and stem feeding on seedling canola (B. napus). Photos: AAFC-Beaverlodge-Otani
Remember, the Action Threshold for flea beetles on canola is 25% of cotyledon leaf area consumed. Watch for shot-hole feeding in seedling canola but also watch the growing point and stems of seedlings which are particularly vulnerable to flea beetle feeding.
If flea beetle densities are high, seedling damage levels can advance quickly – even within the same day! The cotyledon stage of canola is vulnerable to flea beetle feeding.
Estimating flea beetle feeding damage can be challenging. Using a visual guide to estimate damage can be helpful. Use the two images (copied below for reference) produced by Dr. J. Soroka (AAFC-Saskatoon) to help estimate percent of leaf area consumed for canola seedlings – take Figures 2 and 3 scouting!
Figure 2. Canola cotyledons with various percentages of leaf area consume owing to flea beetle feeding damage (Photo: Soroka & Underwood, AAFC-Saskatoon).Figure 3. Percent leaf area consumed by flea beetles feeding on canola seedlings (Photo: Soroka & Underwood, AAFC-Saskatoon).
Flea beetles were the Insect of the Week (Wk 02 – May 13, 2024)! Additionally, access biological and pest management information posted by Saskatchewan Agriculture, or Manitoba Agriculture and Resource Development, or the Canola Council of Canada’s Canola Encyclopedia. Refer to the flea beetle page within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018), accessible as a free downloadable PDF in either English or French on our new Field Guides page.
There is one generation of cabbage seedpod weevil (CSPW; Ceutorhynchus obstrictus) per year. The overwintered adult is an ash-grey weevil measuring 3-4mm long (Fig. 1; left photo). Mating and oviposition are quickly followed by eggs hatching within developing canola pods (Fig. 1; right photo). The highly concealed larvae feed within the pod, consuming the developing seeds.
Figure 1. Cabbage seedpod weevil (left) and egg dissected from within a canola pod (right). Photos: the late Dr. Lloyd Dosdall.
Damage: Adult feeding damage to buds is more evident in dry years when canola is unable to compensate for bud loss. Adults mate following a pollen meal then the female will deposit a single egg through the wall of a developing pod or adjacent to a developing seed within the pod (Fig. 1; right photo). Eggs are oval and an opaque white, each measuring ~1mm long. Typically, a single egg is laid per pod although, when CSPW densities are high, two or more eggs may be laid per pod.
There are four larval instar stages of the CSPW and each stage is white and grub-like in appearance ranging up to 5-6mm in length (Fig. 2; left photo). The first instar larva feeds on the cuticle on the outside of the pod while the second instar larva bores into the pod (Fig. 2; right photo, lower pod), feeding on the developing seeds. A single larva consumes about 5 canola seeds. The mature larva chews a small, circular exit hole (Fig. 2; right photo, upper pod) from which it drops to the soil surface and pupation takes place in the soil within an earthen cell. Approximately 10 days later, the new adult emerges to feed on maturing canola pods. Later in the season, these new adults migrate to overwintering sites beyond the field.
Figure 2. Larva feeding amongst developing seeds within canola pod (left) and larval entrance hole (right photo, lower pod) compared to mature larval exit hole (right photo, uppower pod). Photos: the late Dr. Lloyd Dosdall.
Prairie-Wide Monitoring: The annual cabbage seedpod weevil survey is performed in canola at early flower stages using sweep-net collections. Review the prairie-wide historical survey maps for this insect species. Review the PPMN monitoring protocol although the provinces of Alberta, Saskatchewan, and Manitoba have specific survey protocols for their respective network cooperators. Commercial fields where comparatively higher densities of adult cabbage seedpod weevils were observed in 2024 are highlighted yellow, orange, or red in the geospatial map featured in Figure 3. Areas where historically higher densities of cabbage seedpod weevil were observed in 2024 are worth prioritizing in 2025.
Figure 3. Densities of cabbage seedpod weevil (Ceutorhynchus obstrictus) observed in sweep-net samples retrieved from commercial fields of canola (Brassica napus) grown in Saskatchewan, Alberta, and the British Columbia portion of the Peace River region in 2024.
In-Field Monitoring:
Begin sampling when the crop first enters the bud stage and continue through the flowering.
Sweep-net samples should be taken at ten locations within the field with ten 180° sweeps per location.
Count the number of weevils at each location. Samples should be taken in the field perimeter as well as throughout the field.
Adults will invade fields from the margins and if infestations are high in the borders, application of an insecticide to the field margins may be effective in reducing the population to levels below which economic injury will occur.
An insecticide application is recommended when three to four weevils per sweep are collected and has been shown to be the most effective when canola is in the 10 to 20% bloom stage (2-4 days after flowering starts).
Consider making insecticide applications late in the day to reduce the impact on pollinators. Whenever possible, provide advanced warning of intended insecticide applications to commercial beekeepers operating in the vicinity to help protect foraging pollinators.
High numbers of adults in the fall may indicate the potential for economic infestations the following spring.
Albertan growers can report field observations and check the live map for CSPW posted by Alberta Agriculture and Irrigation (screenshot provided below as an example; retrieved 2022Jul28 but will be updated with 2025 reports as season progresses).
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring, adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Spring Pheromone Trap Monitoring of Adult Males: Across the Canadian prairies, spring monitoring is initiated to acquire weekly counts of adult moths (Fig. 1) attracted to pheromone-baited delta traps deployed in fields. Weekly trap interceptions are observed to generate cumulative counts. These cumulative count estimates are broadly categorized to help producers prioritize and time in-field scouting for larvae.
Figure 1. Adult diamondback moth.
In-Field Monitoring:Remove plants in an area measuring 0.1 m² (about 12″ square), beat them onto a clean surface and count the number of larvae (Fig. 2) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
Figure 2. Diamondback larva measuring ~8mm long. Note brown head capsule and forked appearance of prolegs on posterior.
The economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1 m² (approximately 2-3 larvae per plant). Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1 m² (approximately 1-2 larvae per plant).
Figure 3. Diamondback moth pupa within silken cocoon.
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2025.
Degree-days can be used to predict the timing of insect development and plan for pest scouting and management. Degree-days are calculated for different insect species using temperature thresholds specific to their development. Based on research, the temperature threshold for bertha armyworm (Mamestra configurata) development is 7 °C and 352 accumulated degree-days (base 7 °C) are required for overwintered pupae to begin their spring development phase. As of May 25, there are no areas on the prairies that have surpassed the degree-day requirement for pupal development of bertha armyworm (Fig. 1).
Figure 1. Growing degree-day heat units (Base 7 °C) accumulated across the Canadian prairies from April 1 to May 25, 2025.
Pheromone traps used to monitor bertha armyworm are typically set up along canola fields when pupal development reaches 75-80%; the 2024 monitoring season started the week of June 10, 2024. Cumulative counts from sentinel pheromone monitoring sites targeting bertha armyworm moths across the Canadian prairies in 2024 are highlighted as geospatial areas where producers are encouraged to prioritize in-field monitoring in 2025. Areas in Figure 2 highlighted yellow, orange, or especially red hosted pheromone traps that intercepted relatively high cumulative counts of moths in 2024 and should be prioritized for in-field scouting in 2025. Review the prairie-wide historical survey maps for this insect species.
Figure 2. Cumulative weekly counts of Bertha armyworm (Mamestra configurata) moths arising from the 2024 growing season.
Figure 3 includes photos of the various life stages of the bertha armyworm. There is one generation per year and pupae overwinter in the soil (Fig. 3, C). Each growing season, green unitraps utilizing pheromone lures are deployed and checked weekly over a 6-week window. Cumlative counts generated from the pheromone traps are used to estimate subsequent bertha armyworm densities. The cumulative moth count data is compiled using geospatial maps then posted to support and time in-field scouting for damaging populations of larvae by mid-July through to August.
Figure 3. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018), accessible as a free downloadable PDF in either English or French on our new Field Guides page. Also consider reviewing the 2019 Insect of the Week, which featured bertha armyworm and its doppelganger, the clover cutworm!
Unfortunately, prairie canola farmers are very familiar with striped and crucifer flea beetles and the damage they cause.
Striped (above) and crucifer (below) flea beetles and damage symptoms caused by these beetles to the foliage of brassica plants. Both species are established and often are considered pests in Canadian agroecosystems. Photographed by Meghan Vankosky, AAFC-Saskatoon.
In Europe, the cabbage stem flea beetle (Psylliodes chrysocephalus) is known as the most serious pest of oilseed rape, especially winter oilseed rape. Cabbage stem flea beetle can also affect the yield and marketability of brassica vegetables (e.g., kale, cabbage). Managing cabbage stem flea beetles in the United Kingdom is challenging because this species is resistant to pyrethroid insecticides and neonicotinoids are no longer registered for use in Europe.
Cabbage stem flea beetle is not established in Canada.
Cabbage stem beetle can be extremely damaging to brassica crops and can be very difficult to manage. As a result, it is important that we prevent cabbage stem flea beetle from becoming established in Canada.
Life cycle in United Kingdom: Adults of the cabbage stem flea beetle emerge from the pupal stage in early summer (June-July). At this time, adults consume foliage of the host plant. When temperatures are hot in August, adult cabbage stem flea beetles undergo a period of ‘rest’ or aestivation (i.e., summer diapause). Once temperatures have moderated, adults disperse back to the oilseed rape crops from their aestivation sites, continue to feed on host plant leaves and begin to mate.
Egg laying occurs from September to December. As long as temperatures remain above 3°C, eggs will hatch and larval feeding will occur between October and February. The larvae of cabbage stem flea beetles feed in the petioles of the host plant leaves and in the stems of the plants. Larval feeding reduces the vigour of the plants; severe infestations can result in yield losses and plant death. Larval feeding damage increases in March and April when temperatures increase in spring then pupate in the soil near their host plant in May. Adults begin to emerge in June, and the cycle repeats.
Flea Beetles (Chrysomelidae: Phyllotreta species) – Be on the lookout for flea beetle damage resulting from feeding on canola cotyledons but also on the stem. Two species, Phyllotreta striolata and P. cruciferae, will feed on all cruciferous plants but they can cause economic levels of damage in canola during the seedling stages.
Figure 1. Flea beetle feeding inflicted by overwintered adults including ‘shot-hole’ and stem feeding on seedling canola (B. napus). Photos: AAFC-Beaverlodge-Otani
Remember, the Action Threshold for flea beetles on canola is 25% of cotyledon leaf area consumed. Watch for shot-hole feeding in seedling canola but also watch the growing point and stems of seedlings which are particularly vulnerable to flea beetle feeding.
If flea beetle densities are high, seedling damage levels can advance quickly – even within the same day! The cotyledon stage of canola is vulnerable to flea beetle feeding.
Estimating flea beetle feeding damage can be challenging. Using a visual guide to estimate damage can be helpful. Use the two images (copied below for reference) produced by Dr. J. Soroka (AAFC-Saskatoon) to help estimate percent of leaf area consumed for canola seedlings – take Figures 2 and 3 scouting!
Figure 2. Canola cotyledons with various percentages of leaf area consume owing to flea beetle feeding damage (Photo: Soroka & Underwood, AAFC-Saskatoon).Figure 3. Percent leaf area consumed by flea beetles feeding on canola seedlings (Photo: Soroka & Underwood, AAFC-Saskatoon).
Flea beetles were the Insect of the Week (Wk 02 – May 13, 2024)! Additionally, access biological and pest management information posted by Saskatchewan Agriculture, or Manitoba Agriculture and Resource Development, or the Canola Council of Canada’s Canola Encyclopedia. Refer to the flea beetle page within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018), accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Cutworm scouting spans April to late June across the Canadian prairies! Scout fields that are “slow” to emerge, are missing rows, include wilting or yellowing plants, have bare patches, or appear highly attractive to birds – these are areas warranting a closer look. Plan to follow up by walking these areas either very early or late in the day when some cutworm species (or climbing cutworms) move above-ground to feed. Start to dig below the soil surface (1-5 cm deep) near the base of symptomatic plants and also any healthy plants immediately adjacent to missing rows or wilting or clipped plants. Some cutworms feed while remaining just below the soil surface, clipping then pulling the plant below the soil surface as they munch away! If the plant is well-established (e.g., perennial grass or legume), check within the crown plus in the adjacent soil. The culprits could be cutworms, wireworms, or more!
Important: Several species of cutworms (Lepidoptera: Noctuidae) can be present in fields. They range in colour from shiny opaque, to tan, to brownish-red with chevron patterning. A field guide is available to help growers scout and manage the various species of cutworms that can appear in field crops grown on the Canadian prairies. Cutworm Pest of Crops is available free in either English or French! Download a searchable PDF copy to access helpful diagnostic photos plus a table showing which larvae are active at different points in the growing season!
Other vital resources to scout and manage cutworms include:
● For anyone on the Canadian prairies, Manitoba Agriculture’s Cutworms in Field Crops fact sheet includes suggested nominal thresholds for cutworms in several crops (Table 1). The same fact sheet describes important biological information, and provides great cutworm photos to support in-field scouting!
● For Albertans….. If you find cutworms, please consider using the Alberta Insect Pest Monitoring Network’s “2025 Cutworm Reporting Tool” then view the live 2025 cutworm map updated daily. Review the live map to see where cutworms are appearing then prioritize in-field scouting accordingly.
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring, adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Spring Pheromone Trap Monitoring of Adult Males: Across the Canadian prairies, spring monitoring is initiated to acquire weekly counts of adult moths (Fig. 1) attracted to pheromone-baited delta traps deployed in fields. Weekly trap interceptions are observed to generate cumulative counts. These cumulative count estimates are broadly categorized to help producers prioritize and time in-field scouting for larvae.
Figure 1. Adult diamondback moth.
In-Field Monitoring:Remove plants in an area measuring 0.1 m² (about 12″ square), beat them onto a clean surface and count the number of larvae (Fig. 2) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
Figure 2. Diamondback larva measuring ~8mm long. Note brown head capsule and forked appearance of prolegs on posterior.
The economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1 m² (approximately 2-3 larvae per plant). Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1 m² (approximately 1-2 larvae per plant).
Figure 3. Diamondback moth pupa within silken cocoon.
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2025.
Degree-days can be used to predict the timing of insect development and plan for pest scouting and management. Degree-days are calculated for different insect species using temperature thresholds specific to their development. Based on research, the temperature threshold for bertha armyworm (Mamestra configurata) development is 7 °C and 352 accumulated degree-days (base 7 °C) are required for overwintered pupae to begin their spring development phase. As of May 18, much of the prairies has not reached the degree-day requirement for pupal development of bertha armyworm (Fig. 1).
Figure 1. Growing degree-day heat units (Base 7 °C) accumulated across the Canadian prairies as of May 18, 2025.
Pheromone traps used to monitor bertha armyworm are typically set up along canola fields when pupal development reaches 75-80%; the 2024 monitoring season started the week of June 10, 2024.
Figure 2 includes photos of the various life stages of the bertha armyworm. There is one generation per year and pupae overwinter in the soil (Fig. 2, C). Each growing season, green unitraps utilizing pheromone lures are deployed and checked weekly over a 6-week window. Cumlative counts generated from the pheromone traps are used to estimate subsequent bertha armyworm densities. The cumulative moth count data is compiled using geospatial maps then posted to support and time in-field scouting for damaging populations of larvae by mid-July through to August.
Figure 2. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page. Also consider reviewing the 2019 Insect of the Week which featured bertha armyworm and its doppelganger, the clover cutworm!
Flea Beetles (Chrysomelidae: Phyllotreta species) – Be on the lookout for flea beetle damage resulting from feeding on canola cotyledons but also on the stem. Two species, Phyllotreta striolata and P. cruciferae, will feed on all cruciferous plants but they can cause economic levels of damage in canola during the seedling stages.
Figure 1. Flea beetle feeding inflicted by overwintered adults including ‘shot-hole’ and stem feeding on seedling canola (B. napus). Photos: AAFC-Beaverlodge-Otani
Remember, the Action Threshold for flea beetles on canola is 25% of cotyledon leaf area consumed. Watch for shot-hole feeding in seedling canola but also watch the growing point and stems of seedlings which are particularly vulnerable to flea beetle feeding.
If flea beetle densities are high, seedling damage levels can advance quickly – even within the same day! The cotyledon stage of canola is vulnerable to flea beetle feeding.
Estimating flea beetle feeding damage can be challenging. Using a visual guide to estimate damage can be helpful. Use the two images (copied below for reference) produced by Dr. J. Soroka (AAFC-Saskatoon) to help estimate percent of leaf area consumed for canola seedlings – take Figures 2 and 3 scouting!
Figure 2. Canola cotyledons with various percentages of leaf area consume owing to flea beetle feeding damage (Photo: Soroka & Underwood, AAFC-Saskatoon).Figure 3. Percent leaf area consumed by flea beetles feeding on canola seedlings (Photo: Soroka & Underwood, AAFC-Saskatoon).
Invasive insects and other invasive pests can have significant and negative impacts on agroecosystems and increase the cost of crop production. For example, the pea leaf weevil and cabbage seedpod weevil invaded and established in the prairie region in the past 25 years. Both have affected yield and required insecticide application for management.
Managing invasive alien species, including insects, involves: Preparedness, Prevention, Detection, Response and Recovery.
Preparedness, Prevention, and Detection are important steps that can help to keep invasive species from becoming established. Everyone can help to prevent the invasion of insects by following guidelines to avoid the accidental movement or introduction of insects to Canada.
Similarly, everyone can help with early detection of invasive insects. In the Prairie Region, 12 important insect pests to watch out for are included on posters developed by the Canadian Plant Health Council. The poster is also available in French.
This is the last Insect of the Week post of 2024. Thank you for reading the Insect of the Week series this year!
Access the Provincial Insect Pest Report for Wk16 for updates for this economic insect pest.
Remember: in-field scouting is required to apply the economic threshold to manage both this pest and its natural enemies. Use the images below (Fig. 1) to help identify moths from the by-catch that will be retained in the green phermone-baited unitraps.
Figure 1. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Scouting and pest management for diamondback moth depends on in-field counts of larvae per metre2! This means plants need to be pulled and tapped off to assess the number of larvae! Use Figure 1 below to help identify the different stages of the diamondback moth.
Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.
The economic threshold for immature and flowering canola is 100-150 larvae per metre2.
Access the Provincial Insect Pest Report for Wk16 for updates for this economic insect pest.
Scouting and pest management for diamondback moth depends on in-field counts of larvae per metre2! This means plants need to be pulled and tapped off to assess the number of larvae! Use Figure 1 below to help identify the different stages of the diamondback moth.
Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.
The economic threshold for immature and flowering canola is 100-150 larvae per metre2.
Access the Provincial Insect Pest Report for Wk15 for updates for this economic insect pest.
Access the Provincial Insect Pest Report for Wk14 for updates for this economic insect pest.
Remember: in-field scouting is required to apply the economic threshold to manage both this pest and its natural enemies. Use the images below (Fig. 1) to help identify moths from the by-catch that will be retained in the green phermone-baited unitraps.
Figure 1. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Scouting and pest management for diamondback moth depends on in-field counts of larvae per metre2! This means plants need to be pulled and tapped off to assess the number of larvae! Use Figure 1 below to help identify the different stages of the diamondback moth.
Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.
The economic threshold for immature and flowering canola is 100-150 larvae per metre2.
Access the Provincial Insect Pest Report for Wk14 for updates for this economic insect pest.
Access the Provincial Insect Pest Report for Wk14 for updates for this economic pest.
Lygus bugs are polyphagous (i.e., feed on plants belonging to several Families of plants) and multivoltine (i.e., capable of producing multiple generations per year). Both the adult (Fig. 1) and five nymphal instar stages (Fig. 2) are a sucking insect that focuses feeding activities on developing buds, pods and seeds. Adults overwinter in northern climates. The economic threshold for Lygus in canola is applied at late flower and early pod stages.
Recent research in Alberta has resulted in a revision to the thresholds recommended for the management of Lygus in canola. Under ideal growing conditions (i.e., ample moisture) a threshold of 20-30 lygus per 10 sweeps is recommended. Under dry conditions, a lower threshold may be used, however, because drought limits yield potential in canola, growers should be cautious if considering the use of foliar-applied insecticide at lygus densities below the established threshold of 20-30 per 10 sweeps.In drought-affected fields that still support near-average yield potential, a lower threshold of ~20 lygus per 10 sweeps may be appropriate for stressed canola. Even if the current value of canola remains high (e.g., >$19.00 per bu), control at densities of <10 lygus per 10 sweeps is not likely to be economical. Research indicates that lygus numbers below 10 per 10 sweeps (one per sweep) can on occasion increase yield in good growing conditions – likely through plant compensation for a small amount of feeding stress.
Figure 1. Adult Lygus lineolaris (5-6 mm long) (photo: AAFC-Saskatoon).
Figure 2. Fifth instar lygus bug nymph (3-4 mm long) (photo: AAFC-Saskatoon).
Damage: Lygus bugs have piercing-sucking mouthparts and physically damage the plant by puncturing the tissue and sucking plant juices. The plants also react to the toxic saliva that the insects inject when they feed. Lygus bug infestations can cause alfalfa to have short stem internodes, excessive branching, and small, distorted leaves. In canola, lygus bugs feed on buds and blossoms and cause them to drop. They also puncture seed pods and feed on the developing seeds causing them to turn brown and shrivel.
Scouting tips to keep in mind: Begin monitoring canola when it bolts and continues until seeds within the pods are firm. Since adults can move into canola from alfalfa, check lygus bug numbers in canola when nearby alfalfa crops are cut.
Sample the crop for lygus bugs on a sunny day when the temperature is above 20 °C and the crop canopy is dry. With a standard insect net (38 cm diameter), take ten 180 ° sweeps. Count the number of lygus bugs in the net. Sampling becomes more representative IF repeated at multiple spots within a field so sweep in at least 10 locations within a field to estimate the density of lygus bugs.
Biological and monitoring information related to Lygus in field crops is posted by the provinces of Manitoba or Alberta fact sheets or the Prairie Pest Monitoring Network’s monitoring protocol. Also refer to the Lygus pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page. The Canola Council of Canada’s “Canola Encyclopedia” also summarizes Lygus bugs. The Flax Council of Canada includes Lygus bugs in their Insect Pest downloadable PDF chapter plus the Saskatchewan Pulse Growers summarize Lygus bugs in faba beans.
Pieris rapae is known as the imported cabbageworm, the cabbage butterfly, and the cabbage white butterfly. Larvae are green and are covered in short, soft hairs, giving them a velvety appearance. The larvae are the damaging stage of the cabbage white butterfly life cycle. The larvae will eat the leaves and pods of canola and related field crops, but cabbage white butterflies are not considered to be an economic pest of canola.
A group of larvae of the imported cabbageworm (a.k.a. cabbage white butterfly) feeding inside a broccoli crown. Picture by Meghan Vankosky, AAFC-Saskatoon.
The larvae of cabbage white butterflies also consume the leaves of cruciferous weeds and vegetables, like broccoli, cabbage, and rutabaga. In vegetables, feeding damage to the leaves results in jagged holes.
A broccoli plant in a backyard garden with jagged holes in the leaves caused by cabbage white butterfly larvae. At least two larvae are also visible in the picture. Picture by Meghan Vankosky, AAFC-Saskatoon.
Larvae can also tunnel into the heads of vegetables, as pictured below. The combination of feeding damage to the heads and build-up of frass (fecal matter) can affect the marketability of vegetables infested with cabbage white butterfly larvae.
A broccoli crown with two holes in the head where larvae of the cabbage white butterfly tunneled into the center of the crown. The larvae pictured above were found feeding inside this broccoli crown. Picture by Meghan Vankosky, AAFC-Saskatoon.
Adult cabbage white butterflies do not damage crops as they feed on nectar. The white butterflies have black-tipped forewings with black spots and are often seen flying around canola and mustard fields and around gardens where cruciferous vegetables are grown. In 2023, cabbage white butterflies were especially numerous in southeastern Saskatchewan in August.
An adult cabbage white butterfly. Picture by David Cappaert, bugwood.org.
Scouting and pest management for diamondback moth depends on in-field counts of larvae per metre2! This means plants need to be pulled and tapped off to assess the number of larvae! Use Figure 1 below to help identify the different stages of the diamondback moth.
Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.
The economic threshold for immature and flowering canola is 100-150 larvae per metre2.
Access the Provincial Insect Pest Report for Wk13 for updates for this economic insect pest.
Canola flower midge overwinter inside cocoons in the soil and adults usually begin to emerge in late June and can be found until late August, so long as canola flowers are available. There are likely two generations per year, but emergence of adults also seems to be relatively unsynchronized and may not always occur in distinct peaks that align with discrete generations. Canola flower midge adults are not damaging to their host plants. The presence of adult canola flower midge can be detected using pheromone-baited traps.
A canola flower with canola flower midge larvae developing inside. Picture by Jon Williams, AAFC-Saskatoon.
Adult female canola flower midge lay their eggs on developing canola buds before they bloom. The larvae develop in groups inside the flower, resulting in a galled flower that does not produce a pod.
Galled flowers, resulting from larval feeding by canola flower midge on a canola raceme. Picture by Boyd Mori, University of Alberta.
Galled flowers can occur at any point along a canola raceme, with early emerging adults laying eggs on the first flowers to open. The galled flowers tend to remain ‘stuck’ on the raceme, even after the larvae have dropped to the soil to pupate. A monitoring protocol for canola flower midge, based on galled flowers can be used to estimate population densities in canola fields.
A canola raceme with galled flowers (circled), caused by canola flower midge in the field. Picture by Boyd Mori, University of Alberta.
Canola flower midge was described in the scientific literature in a paper published by Mori et al. in 2019, after its identify was confirmed in 2016. There is still a lot to learn about canola flower midge, including its potential to have economic impacts on canola yield.
Please read more about canola flower midge in previous Insect of the Week posts published in 2018 and 2021 or visit the Canola Council of Canada Canola Encyclopedia for more information about canola flower midge.
Aphid populations can quickly increase at this point in the season and particularly when growing conditions are warm and dry. Access the Provincial Insect Pest Report for Wk12 to remain alert to areas and crops suffering from aphid pest pressure.
Figure 1. Pea aphid adults (each 3-4 mm long) and nymph. Photo: M. Dolinski.
Alternatively, several aphid pest species are described in the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) and is accessible as a free downloadable PDF in either English or French on our Field Guides page. PDF copies of the individual pages have been linked below to access quickly: • Corn leaf aphid or Rhopalosiphum maidis (Fitch) • English grain aphid or Sitobion (Macrosiphum) avenae (Fabricius) • Oat-birdcherry aphid or Rhopalosiphum padi (Linnaeus) • Pea aphid or Acyrthosiphon pisum (Harris) • Potato aphid or Macrosiphum euphorbiae (Thomas) • Soybean aphid or Aphis glycines (Matsumura) • Turnip aphid or Lipaphis erysimi (Kaltenbach) • Sugar beet root aphid or Pemphigus betae Doane • Russian wheat aphid or Diuraphis noxia (Mordvilko)
Scouting for canola flower midge tends to be easiest as the flowering stage of canola ends and pod development begins. Female canola flower midge lay eggs on developing canola buds and larvae develop inside the buds, resulting in galled flowers that do not open or produce pods.
Although canola flower midge does not appear to occur at densities that cause economic damage, scouting for canola flower midge will help to monitor population growth at the local scale to avoid surprises in the future. The monitoring protocol used during our survey from 2017-2019 is now available online so that everyone can scout for canola flower midge.
Check out the Canola Flower Midge Scouting post from Week 10 in 2023 for pictures of damage caused by this insect and to see a map of canola flower midge distribution.
Compare canola flower midge damage to the closely related Swede midge which was featured as Wk12’s Insect of the Week.
Access the Provincial Insect Pest Report for Wk12 for updates for this economic insect pest.
Weekly Pheromone-baited Trapping Results – Early season detection of bertha armyworm is improved through the use of pheromone-baited unitraps traps deployed in fields across the Canadian prairies. Access the Provincial Insect Pest Report for Wk12 for updates for this economic insect pest.
Remember: in-field scouting is required to apply the economic threshold to manage both this pest and its natural enemies. Use the images below (Fig. 1) to help identify moths from the by-catch that will be retained in the green phermone-baited unitraps.
Figure 1. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Scouting and pest management for diamondback moth depends on in-field counts of larvae per metre2! This means plants need to be pulled and tapped off to assess the number of larvae! Use Figure 1 below to help identify the different stages of the diamondback moth.
Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.
The economic threshold for immature and flowering canola is 100-150 larvae per metre2.
Access the Provincial Insect Pest Report for Wk12 for updates for this economic insect pest.
On the Canadian prairies, lygus bugs (Heteroptera: Miridae) are normally a complex of several native species usually including Lygus lineolaris, L. keltoni, L. borealis, L. elisus although several more species are distributed throughout Canada. The species of Lygus forming the “complex” can vary by host plant, by region or even seasonally.
Lygus bugs are polyphagous (i.e., feed on plants belonging to several Families of plants) and multivoltine (i.e., capable of producing multiple generations per year). Both the adult (Fig. 1) and five nymphal instar stages (Fig. 2) are a sucking insect that focuses feeding activities on developing buds, pods and seeds. Adults overwinter in northern climates. The economic threshold for Lygus in canola is applied at late flower and early pod stages.
Recent research in Alberta has resulted in a revision to the thresholds recommended for the management of Lygus in canola. Under ideal growing conditions (i.e., ample moisture) a threshold of 20-30 lygus per 10 sweeps is recommended. Under dry conditions, a lower threshold may be used, however, because drought limits yield potential in canola, growers should be cautious if considering the use of foliar-applied insecticide at lygus densities below the established threshold of 20-30 per 10 sweeps.In drought-affected fields that still support near-average yield potential, a lower threshold of ~20 lygus per 10 sweeps may be appropriate for stressed canola. Even if the current value of canola remains high (e.g., >$19.00 per bu), control at densities of <10 lygus per 10 sweeps is not likely to be economical. Research indicates that lygus numbers below 10 per 10 sweeps (one per sweep) can on occasion increase yield in good growing conditions – likely through plant compensation for a small amount of feeding stress.
Figure 1. Adult Lygus lineolaris (5-6 mm long) (photo: AAFC-Saskatoon).
Figure 2. Fifth instar lygus bug nymph (3-4 mm long) (photo: AAFC-Saskatoon).
Damage: Lygus bugs have piercing-sucking mouthparts and physically damage the plant by puncturing the tissue and sucking plant juices. The plants also react to the toxic saliva that the insects inject when they feed. Lygus bug infestations can cause alfalfa to have short stem internodes, excessive branching, and small, distorted leaves. In canola, lygus bugs feed on buds and blossoms and cause them to drop. They also puncture seed pods and feed on the developing seeds causing them to turn brown and shrivel.
Scouting tips to keep in mind: Begin monitoring canola when it bolts and continues until seeds within the pods are firm. Since adults can move into canola from alfalfa, check lygus bug numbers in canola when nearby alfalfa crops are cut.
Sample the crop for lygus bugs on a sunny day when the temperature is above 20 °C and the crop canopy is dry. With a standard insect net (38 cm diameter), take ten 180 ° sweeps. Count the number of lygus bugs in the net. Sampling becomes more representative IF repeated at multiple spots within a field so sweep in at least 10 locations within a field to estimate the density of lygus bugs.
Biological and monitoring information related to Lygus in field crops is posted by the provinces of Manitoba or Alberta fact sheets or the Prairie Pest Monitoring Network’s monitoring protocol. Also refer to the Lygus pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page. The Canola Council of Canada’s “Canola Encyclopedia” also summarizes Lygus bugs. The Flax Council of Canada includes Lygus bugs in their Insect Pest downloadable PDF chapter plus the Saskatchewan Pulse Growers summarize Lygus bugs in faba beans.
To the very best of our knowledge, swede midge are NOT currently present in western Canada.
Adult and larval swede midge on a growing point of a canola plant; note the characteristic purpling of the infested growing point. Picture by Jon Williams, AAFC-Saskatoon.
Every year, the Prairie Pest Monitoring Network coordinates a pheromone-based monitoring program for swede midge because of the high risk that swede midge poses to the canola industry in western Canada. Swede midge is also a threat to the vegetable industry in western Canada, as it can use broccoli, cabbage, cauliflower, and other crucifer vegetables as a host.
Adult swede midge do not damage canola or crucifer vegetables, but females lay eggs on the growing points of the plant. When eggs are laid on the florets of canola, some flowers on the raceme may develop normally, but the others become ‘fused’ together as a result of swede midge larval feeding.
Flower buds ‘fused’ together on a floret, the result of infestation by swede midge. Picture by Jon Williams, AAFC-Saskatoon.
Female swede midge can also lay eggs where new racemes or branches grow off the main stem of canola plants. In this situation, larval feeding stops the growth of the new raceme, leaving a stunted raceme with crumpled leaves that often turn purple.
Crumpled and purple-coloured new growth on a canola plant, as in the circled part of the picture, is a symptom of infestation by swede midge. Picture by Meghan Vankosky, AAFC-Saskatoon.
In vegetable crops like broccoli, cauliflower, and cabbage, larval feeding on the growing point of the plant prevents development of the harvestable heads. Very high yield losses have been observed in eastern Canada and the eastern United States in vegetable crops because of swede midge damage.
So far, swede midge is not an established pest in western Canada and we have not found it in pheromone traps in 10+ years of monitoring in Alberta, Saskatchewan, or Manitoba. But, swede midge is slowly moving farther and farther west in the United States. To protect the canola and vegetable industries in western Canada, it is very important to be vigilant and continue to monitor for swede midge.
If you find damage on canola or crucifer vegetable crops that looks like it could be swede midge damage, please report it. You can email meghan.vankosky@agr.gc.ca with pictures or questions.
Scouting and pest management for diamondback moth depends on in-field counts of larvae per metre2! This means plants need to be pulled and tapped off to assess the number of larvae! Use Figure 1 below to help identify the different stages of the diamondback moth.
Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.
The economic threshold for immature and flowering canola is 100-150 larvae per metre2.
Access the Provincial Insect Pest Report for Wk11 for updates for this economic insect pest.
Weekly Pheromone-baited Trapping Results – Early season detection of bertha armyworm is improved through the use of pheromone-baited unitraps traps deployed in fields across the Canadian prairies. Access the Provincial Insect Pest Report for Wk09 for updates for this economic insect pest.
Remember: in-field scouting is required to apply the economic threshold to manage both this pest and its natural enemies. Use the images below (Fig. 1) to help identify moths from the by-catch that will be retained in the green phermone-baited unitraps.
Figure 1. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Aphid populations can quickly increase at this point in the season and particularly when growing conditions are warm and dry. Over the years, both the Weekly Updates and Insect of the Week included aphid-related information so here’s a list of these items to access when scouting fields:
On the Canadian prairies, lygus bugs (Heteroptera: Miridae) are normally a complex of several native species usually including Lygus lineolaris, L. keltoni, L. borealis, L. elisus although several more species are distributed throughout Canada. The species of Lygus forming the “complex” can vary by host plant, by region or even seasonally.
Lygus bugs are polyphagous (i.e., feed on plants belonging to several Families of plants) and multivoltine (i.e., capable of producing multiple generations per year). Both the adult (Fig. 1) and five nymphal instar stages (Fig. 2) are a sucking insect that focuses feeding activities on developing buds, pods and seeds. Adults overwinter in northern climates. The economic threshold for Lygus in canola is applied at late flower and early pod stages.
Recent research in Alberta has resulted in a revision to the thresholds recommended for the management of Lygus in canola. Under ideal growing conditions (i.e., ample moisture) a threshold of 20-30 lygus per 10 sweeps is recommended. Under dry conditions, a lower threshold may be used, however, because drought limits yield potential in canola, growers should be cautious if considering the use of foliar-applied insecticide at lygus densities below the established threshold of 20-30 per 10 sweeps.In drought-affected fields that still support near-average yield potential, a lower threshold of ~20 lygus per 10 sweeps may be appropriate for stressed canola. Even if the current value of canola remains high (e.g., >$19.00 per bu), control at densities of <10 lygus per 10 sweeps is not likely to be economical. Research indicates that lygus numbers below 10 per 10 sweeps (one per sweep) can on occasion increase yield in good growing conditions – likely through plant compensation for a small amount of feeding stress.
Figure 1. Adult Lygus lineolaris (5-6 mm long) (photo: AAFC-Saskatoon).
Figure 2. Fifth instar lygus bug nymph (3-4 mm long) (photo: AAFC-Saskatoon).
Damage: Lygus bugs have piercing-sucking mouthparts and physically damage the plant by puncturing the tissue and sucking plant juices. The plants also react to the toxic saliva that the insects inject when they feed. Lygus bug infestations can cause alfalfa to have short stem internodes, excessive branching, and small, distorted leaves. In canola, lygus bugs feed on buds and blossoms and cause them to drop. They also puncture seed pods and feed on the developing seeds causing them to turn brown and shrivel.
Scouting tips to keep in mind: Begin monitoring canola when it bolts and continues until seeds within the pods are firm. Since adults can move into canola from alfalfa, check lygus bug numbers in canola when nearby alfalfa crops are cut.
Sample the crop for lygus bugs on a sunny day when the temperature is above 20 °C and the crop canopy is dry. With a standard insect net (38 cm diameter), take ten 180 ° sweeps. Count the number of lygus bugs in the net. Sampling becomes more representative IF repeated at multiple spots within a field so sweep in at least 10 locations within a field to estimate the density of lygus bugs.
Biological and monitoring information related to Lygus in field crops is posted by the provinces of Manitoba or Alberta fact sheets or the Prairie Pest Monitoring Network’s monitoring protocol. Also refer to the Lygus pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page. The Canola Council of Canada’s “Canola Encyclopedia” also summarizes Lygus bugs. The Flax Council of Canada includes Lygus bugs in their Insect Pest downloadable PDF chapter plus the Saskatchewan Pulse Growers summarize Lygus bugs in faba beans.
Scouting for canola flower midge tends to be easiest as the flowering stage of canola ends and pod development begins. Female canola flower midge lay eggs on developing canola buds and larvae develop inside the buds, resulting in galled flowers that do not open or produce pods.
Although canola flower midge does not appear to occur at densities that cause economic damage, scouting for canola flower midge will help to monitor population growth at the local scale to avoid surprises in the future. The monitoring protocol used during our survey from 2017-2019 is now available online so that everyone can scout for canola flower midge.
Check out the Canola Flower Midge Scouting post from Week 10 in 2023 for pictures of damage caused by this insect and to see a map of canola flower midge distribution.
The Lygus bug pest complex includes at least 5 species, including the tarnished plant bug (Lygus lineolaris), Lygus keltoni, and Lygus borealis. Lygus bugs have an upside down triangle on their backs and adults are about 5-6 mm long; their colour varies depending on the species and their stage of development. Lygus bugs have a fairly wide host range, but canola, soybean and alfalfa are prone to yield losses resulting from Lygus feeding damage.
An adult Lygus bug, with the characteristic triangle on the back. Picture by AAFC-Saskatoon. Lygus nymphs of different instars and an adult Lygus bug. Pictures by Hector Carcamo, AAFC-Lethbridge.
The nymphs and adults use piercing and sucking mouthparts to drink from their host plants. They prefer to feed on new growth and reproductive tissues, as these are more nutrient-rich than other plant structures. Feeding by Lygus bugs can result in bud-blasting, where developing buds or flowers do not continue to develop and drop from the plant. If Lygus bugs feed on developing seeds, the seeds become shriveled, reducing yield quality and quantity. Watch for circular, black scars on canola pods, as these are an indicator that Lygus bugs has been feeding on canola pods, and probably on the seeds inside the pods.
Top: A canola raceme with bud blasting symptoms typical of Lygus feeding injury. Bottom: Canola seeds damaged by Lygus feeding (left, middle) and healthy canola seeds (right). All pictures by R.A. Butts, AAFC-Lethbridge.
In addition to direct yield losses due to Lygus feeding damage, the wounds left by their mouthparts make plant tissues vulnerable to infection by pathogens. Because Lyugs bugs inject digestive enzymes into the plant to help break down plant tissues for consumption, they can also vector plant diseases.
Use a sweep net to scout for Lygus bugs in canola and alfalfa crops. The PPMN has a monitoring protocol available here.
In canola, scout as flowering is complete and pods are beginning to ripen. Take 10 sweeps at 15 locations in the field and estimate the number of lygus nymphs and adults per sweep. Recent research suggests that the economic threshold to avoid yield loss in canola is 2-3 Lygus bugs per sweep; check out the Canola Council of Canada, Manitoba Agriculture, and Alberta Agriculture and IrrigationLygus pages for more information about Lygus bugs and economic thresholds in canola.
In alfalfa, scout at the start of the bud stage by taking 5 sweeps in at least 15 locations per field and estimating the number of Lygus nymphs and adults per sweep. In seed alfalfa fields, the economic threshold is 8 Lygus per sweep in at least 40 sweeps.
For more information about Lygus bugs, visit previous Insect of the Week articles and find the Lygus page in Field Crop and Forage Pests and their Natural Enemies in Western Canada, available in English and in French. SaskPulse also recently published an overview of Lygus impacts on pulse crops written by Jennifer Bogdan.
Scouting and pest management for diamondback moth depends on in-field counts of larvae per metre2! This means plants need to be pulled and tapped off to assess the number of larvae! Use Figure 1 below to help identify the different stages of the diamondback moth.
Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.
The economic threshold for immature and flowering canola is 100-150 larvae per metre2.
Access the Provincial Insect Pest Report for Wk09 for updates for this economic insect pest.
There is one generation of cabbage seedpod weevil (CSPW; Ceutorhynchus obstrictus) per year. The overwintered adult is an ash-grey weevil measuring 3-4mm long (e.g., lower left photo). Mating and oviposition are quickly followed by eggs hatching within developing canola pods (e.g., lower right photo). The highly concealed larvae feed within the pod, consuming the developing seeds.
Damage: Adult feeding damage to buds is more evident in dry years when canola is unable to compensate for bud loss. Adults mate following a pollen meal then the female will deposit a single egg through the wall of a developing pod or adjacent to a developing seed within the pod (refer to lower right photo). Eggs are oval and an opaque white, each measuring ~1mm long. Typically a single egg is laid per pod although, when CSPW densities are high, two or more eggs may be laid per pod.
There are four larval instar stages of the CSPW and each stage is white and grub-like in appearance ranging up to 5-6mm in length (refer to lower left photo). The first instar larva feeds on the cuticle on the outside of the pod while the second instar larva bores into the pod, feeding on the developing seeds. A single larva consumes about 5 canola seeds. The mature larva chews a small, circular exit hole from which it drops to the soil surface and pupation takes place in the soil within an earthen cell. Approximately 10 days later, the new adult emerges to feed on maturing canola pods. Later in the season, these new adults migrate to overwintering sites beyond the field.
Monitoring:
Begin sampling when the crop first enters the bud stage and continue through the flowering.
Sweep-net samples should be taken at ten locations within the field with ten 180° sweeps per location.
Count the number of weevils at each location. Samples should be taken in the field perimeter as well as throughout the field.
Adults will invade fields from the margins and if infestations are high in the borders, application of an insecticide to the field margins may be effective in reducing the population to levels below which economic injury will occur.
An insecticide application is recommended when three to four weevils per sweep are collected and has been shown to be the most effective when canola is in the 10 to 20% bloom stage (2-4 days after flowering starts).
Consider making insecticide applications late in the day to reduce the impact on pollinators. Whenever possible, provide advanced warning of intended insecticide applications to commercial beekeepers operating in the vicinity to help protect foraging pollinators.
High numbers of adults in the fall may indicate the potential for economic infestations the following spring.
Albertan growers can report and check the live map for CSPW posted by Alberta Agriculture and Irrigation (screenshot provided below for reference; retrieved 2024Jul04).
Weekly Pheromone-baited Trapping Results – Early season detection of bertha armyworm is improved through the use of pheromone-baited unitraps traps deployed in fields across the Canadian prairies. Access the Provincial Insect Pest Report for Wk09 for updates for this economic insect pest.
Remember: in-field scouting is required to apply the economic threshold to manage both this pest and its natural enemies. Use the images below (Fig. 1) to help identify moths from the by-catch that will be retained in the green phermone-baited unitraps.
Figure 1. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Cabbage seedpod weevil, Ceutorhynchus obstrictus, is an invasive alien insect. Cabbage seedpod weevil is present in Alberta, Saskatchewan and Manitoba but it has not yet been detected in the Peace River region. Both the adult and larval stages of cabbage seedpod weevil feed on canola, brown mustard, and wild mustard. Feeding by the larvae generally has a greater impact on crop yields than feeding by the adults.
A dead adult cabbage seedpod weevil, posed for a picture by Jon Williams, AAFC-Saskatoon.
Cabbage seedpod weevil larval feeding results in direct yield loss because the developing larvae consume developing canola and brown mustard seeds inside the pods. Each larva can eat up to 5 seeds during its development. In addition to the direct yield loss caused by the larvae, pods infested by cabbage seedpod weevil are more likely to shatter during harvest and are prone to secondary infection by fungal pathogens.
A cabbage seedpod weevil larva inside a canola pod, where it developed by consuming canola seeds. Picture by AAFC.
Adult cabbage seedpod weevil will feed on a variety of brassica species, both crops and weeds, but does not use yellow mustard as a host plant. In spring, adult cabbage seedpod weevil can be found feeding in patches of flix weed, hoary cress, stinkweed, and volunteer canola. The adults then disperse into canola and brown mustard crops, where they eat flower buds and flowers. This feeding damage can result in bud-blasting, but does not typically impact crop yields. The new generation of cabbage seedpod weevil adults that emerge in late summer can also feed on pods before the crops are harvested.
Exit holes in canola pods that were chewed by cabbage seedpod weevil larvae. Larvae exit the pods to pupate in the soil once larval development is completed. Picture by AAFC.
Scout for adult cabbage seedpod weevil as they disperse into canola fields and prepare to lay eggs. When scouting, take ten 180° sweeps at ten locations in the field. Count the adult weevils after each set of 10 sweeps and calculate the average number of adult cabbage seedpod weevil per sweep. Carcamo et al. published new research about cabbage seedpod weevil in 2019, where they found that the economic threshold for cabbage seedpod weevil is 2.5-4 adult weevils per sweep.
For more information about cabbage seedpod weevil, visit previous Insect of the Week articles and find the cabbage seedpod weevil page in Field Crop and Forage Pests and their Natural Enemies in Western Canada, available in English and in French.
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2024.
Scouting and pest management for diamondback moth depends on in-field counts of larvae per metre2! This means plants need to be pulled and tapped off to assess the number of larvae! Use Figure 1 below to help identify the different stages of the diamondback moth.
Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.
There is one generation of cabbage seedpod weevil (CSPW; Ceutorhynchus obstrictus) per year. The overwintered adult is an ash-grey weevil measuring 3-4mm long (e.g., lower left photo). Mating and oviposition are quickly followed by eggs hatching within developing canola pods (e.g., lower right photo). The highly concealed larvae feed within the pod, consuming the developing seeds.
Damage: Adult feeding damage to buds is more evident in dry years when canola is unable to compensate for bud loss. Adults mate following a pollen meal then the female will deposit a single egg through the wall of a developing pod or adjacent to a developing seed within the pod (refer to lower right photo). Eggs are oval and an opaque white, each measuring ~1mm long. Typically a single egg is laid per pod although, when CSPW densities are high, two or more eggs may be laid per pod.
There are four larval instar stages of the CSPW and each stage is white and grub-like in appearance ranging up to 5-6mm in length (refer to lower left photo). The first instar larva feeds on the cuticle on the outside of the pod while the second instar larva bores into the pod, feeding on the developing seeds. A single larva consumes about 5 canola seeds. The mature larva chews a small, circular exit hole from which it drops to the soil surface and pupation takes place in the soil within an earthen cell. Approximately 10 days later, the new adult emerges to feed on maturing canola pods. Later in the season, these new adults migrate to overwintering sites beyond the field.
Monitoring:
Begin sampling when the crop first enters the bud stage and continue through the flowering.
Sweep-net samples should be taken at ten locations within the field with ten 180° sweeps per location.
Count the number of weevils at each location. Samples should be taken in the field perimeter as well as throughout the field.
Adults will invade fields from the margins and if infestations are high in the borders, application of an insecticide to the field margins may be effective in reducing the population to levels below which economic injury will occur.
An insecticide application is recommended when three to four weevils per sweep are collected and has been shown to be the most effective when canola is in the 10 to 20% bloom stage (2-4 days after flowering starts).
Consider making insecticide applications late in the day to reduce the impact on pollinators. Whenever possible, provide advanced warning of intended insecticide applications to commercial beekeepers operating in the vicinity to help protect foraging pollinators.
High numbers of adults in the fall may indicate the potential for economic infestations the following spring.
Albertan growers can report and check the live map for CSPW posted by Alberta Agriculture and Irrigation (screenshot provided below for reference; retrieved 2024Jul04).
Weekly Pheromone-baited Trapping Results – Early season detection of bertha armyworm is improved through the use of pheromone-baited unitraps traps deployed in fields across the Canadian prairies. Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2024.
Remember: in-field scouting is required to apply the economic threshold to manage both this pest and its natural enemies. Use the images below (Fig. 1) to help identify moths from the by-catch that will be retained in the green phermone-baited unitraps.
Figure 1. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
There is one generation of cabbage seedpod weevil (CSPW; Ceutorhynchus obstrictus) per year. The overwintered adult is an ash-grey weevil measuring 3-4mm long (e.g., lower left photo). Mating and oviposition are quickly followed by eggs hatching within developing canola pods (e.g., lower right photo). The highly concealed larvae feed within the pod, consuming the developing seeds.
Damage: Adult feeding damage to buds is more evident in dry years when canola is unable to compensate for bud loss. Adults mate following a pollen meal then the female will deposit a single egg through the wall of a developing pod or adjacent to a developing seed within the pod (refer to lower right photo). Eggs are oval and an opaque white, each measuring ~1mm long. Typically a single egg is laid per pod although, when CSPW densities are high, two or more eggs may be laid per pod.
There are four larval instar stages of the CSPW and each stage is white and grub-like in appearance ranging up to 5-6mm in length (refer to lower left photo). The first instar larva feeds on the cuticle on the outside of the pod while the second instar larva bores into the pod, feeding on the developing seeds. A single larva consumes about 5 canola seeds. The mature larva chews a small, circular exit hole from which it drops to the soil surface and pupation takes place in the soil within an earthen cell. Approximately 10 days later, the new adult emerges to feed on maturing canola pods. Later in the season, these new adults migrate to overwintering sites beyond the field.
Monitoring:
Begin sampling when the crop first enters the bud stage and continue through the flowering.
Sweep-net samples should be taken at ten locations within the field with ten 180° sweeps per location.
Count the number of weevils at each location. Samples should be taken in the field perimeter as well as throughout the field.
Adults will invade fields from the margins and if infestations are high in the borders, application of an insecticide to the field margins may be effective in reducing the population to levels below which economic injury will occur.
An insecticide application is recommended when three to four weevils per sweep are collected and has been shown to be the most effective when canola is in the 10 to 20% bloom stage (2-4 days after flowering starts).
Consider making insecticide applications late in the day to reduce the impact on pollinators. Whenever possible, provide advanced warning of intended insecticide applications to commercial beekeepers operating in the vicinity to help protect foraging pollinators.
High numbers of adults in the fall may indicate the potential for economic infestations the following spring.
Albertan growers can report and check the live map for CSPW posted by Alberta Agriculture and Irrigation (screenshot provided below for reference; retrieved 2024Jun27).
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
By this week, a second generation of adult diamondback moth should be active in parts of the prairies.
Pheromone-baited delta traps housing sticky cards are used to monitor diamondback moth across the Canadian prairies. Research has shown that cumulative counts > 25 moths indicate elevated risk. In those areas, it then becomes important to scout and assess larval densities.
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2024.
Scouting and pest management for diamondback moth depends on in-field counts of larvae per metre2! This means plants need to be pulled and tapped off to assess the number of larvae! Use Figure 1 below to help identify the different stages of the diamondback moth.
Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.
Pheromone traps used to monitor bertha armyworm are typically set up along canola fields when pupal development reaches 75-80%; the 2024 monitoring season started the week of June 10, 2024. Use the images below (Fig. 1) to help identify moths from the by-catch that will be retained in the green phermone-baited unitraps.
Figure 1. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2024.
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
During bertha armyworm outbreaks, canola and mustard crops typically experience the most damage and highest economic losses. However, bertha armyworm also eat alfalfa, peas, quinoa, flax, potatoes, and other crop and weed plants. Adult moths do not damage crops. Larvae consume green plant tissues using their chewing mouthparts.
A canola field stripped of leaves and with damage to pods following a severe infestation of bertha armyworm in Manitoba. Picture by John Gavloski, Manitoba Agriculture.
Bertha armyworm larvae are cause for concern when they occur in high numbers when canola pods are developing and maturing. This is because ‘mature’ bertha armyworm larvae (e.g., 5th and 6th instars) will start eating developing canola pods. Pod damage includes debarking, which can result in pod shatter before or during harvest. Bertha armyworm larvae can also directly consume the developing seeds. Bertha armyworm larvae can also clip flowers and bolls off of flax plants.
A bertha armyworm caterpillar in the process of feeding on a canola pod. Picture by John Gavloski, Manitoba Agriculture. Bertha armyworm damage, caused by larvae, to canola pods. Picture by Shelley Barkley, Alberta Agriculture and Irrigation.
The Prairie Pest Monitoring Network, Alberta Agriculture and Irrigation, Saskatchewan Ministry of Agriculture and Manitoba Agriculture coordinate an annual monitoring program for bertha armyworm using pheromone traps. The 2024 monitoring season started the week of June 10 and will continue until late July. Thank you to all of the volunteers across the prairies who are hosting bertha armyworm pheromone traps!
The number of bertha armyworm moths captured in the pheromone traps serves as an estimate of local risk. Watch for information about the bertha armyworm monitoring program from the PPMN Weekly Updates and the provincial insect updates. If trap catches indicate possible risk, then scout canola crops for larvae using the bertha armyworm monitoring protocol found on the PPMN Protocol page. Information to calculate economic thresholds can also be found in the monitoring protocol.
The life cycle of bertha armyworm: A) eggs, B) larval stage, C) pupal stage, and D) adult stage. The larval stage is the only stage that actively damages crops. All pictures by Jon Williams, AAFC-Saskatoon.
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
The week of May 27, 2024, very mature larvae were retrieved in flixweed in southern Alberta (Barkley, pers. comm. 2024). Thus, a second generation of adult diamondback moth is likely active in southern parts of the prairies.
Pheromone-baited Delta traps housing sticky cards are used to monitor diamondback moth across the Canadian prairies. Research has shown that cumulative counts > 25 moths indicate elevated risk. In those areas, it then becomes important to scout and assess larval densities.
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2024.
Scouting and pest management for diamondback moth depends on in-field counts of larvae per metre2! This means plants need to be pulled and tapped off to assess the number of larvae! Use Figure 1 below to help identify the different stages of diamondback moth.
Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.
Biological and monitoring information for DBM (including tips for scouting and economic thresholds) is posted by Manitoba Agriculture, Saskatchewan Agriculture, and the Prairie Pest Monitoring Network. Also, refer to the diamondback moth pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our Field Guides page.
There is one generation of cabbage seedpod weevil (CSPW; Ceutorhynchus obstrictus) per year. The overwintered adult is an ash-grey weevil measuring 3-4mm long (e.g., lower left photo). Mating and oviposition are quickly followed by eggs hatching within developing canola pods (e.g., lower right photo). The highly concealed larvae feed within the pod, consuming the developing seeds.
Damage: Adult feeding damage to buds is more evident in dry years when canola is unable to compensate for bud loss. Adults mate following a pollen meal then the female will deposit a single egg through the wall of a developing pod or adjacent to a developing seed within the pod (refer to lower right photo). Eggs are oval and an opaque white, each measuring ~1mm long. Typically a single egg is laid per pod although, when CSPW densities are high, two or more eggs may be laid per pod.
There are four larval instar stages of the CSPW and each stage is white and grub-like in appearance ranging up to 5-6mm in length (refer to lower left photo). The first instar larva feeds on the cuticle on the outside of the pod while the second instar larva bores into the pod, feeding on the developing seeds. A single larva consumes about 5 canola seeds. The mature larva chews a small, circular exit hole from which it drops to the soil surface and pupation takes place in the soil within an earthen cell. Approximately 10 days later, the new adult emerges to feed on maturing canola pods. Later in the season, these new adults migrate to overwintering sites beyond the field.
Monitoring:
Begin sampling when the crop first enters the bud stage and continue through the flowering.
Sweep-net samples should be taken at ten locations within the field with ten 180° sweeps per location.
Count the number of weevils at each location. Samples should be taken in the field perimeter as well as throughout the field.
Adults will invade fields from the margins and if infestations are high in the borders, application of an insecticide to the field margins may be effective in reducing the population to levels below which economic injury will occur.
An insecticide application is recommended when three to four weevils per sweep are collected and has been shown to be the most effective when canola is in the 10 to 20% bloom stage (2-4 days after flowering starts).
Consider making insecticide applications late in the day to reduce the impact on pollinators. Whenever possible, provide advanced warning of intended insecticide applications to commercial beekeepers operating in the vicinity to help protect foraging pollinators.
High numbers of adults in the fall may indicate the potential for economic infestations the following spring.
Albertan growers can report and check the live map for CSPW posted by Alberta Agriculture and Irrigation (screenshot provided below as an example; retrieved 2022Jul28).
Pheromone traps used to monitor bertha armyworm are typically set up along canola fields when pupal development reaches 75-80%; the 2024 monitoring season started the week of June 10, 2024.
Use the images below (Fig. 1) to help identify moths from the by-catch that will be retained in the green phermone-baited unitraps.
Figure 1. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2024.
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Diamondback moth larvae have voracious appetites for canola, mustard, flix weed, and vegetables including broccoli, brussels sprouts, cauliflower, and kale. They are specialists of plants in the family Brassicaceae (formerly Cruciferae).
When diamondback moth larvae first hatch, they are very small and tunnel inside the leaves to eat, resulting in damage that looks like shot-holes and leaf mines.
The life cycle of diamondback moth and damage characteristic of B) first and second instar larvae that tunnel and mine leaves, often leaving ‘shot-hole’ damage, and C) third and fourth instar larvae that can eat entire leaves, except for the leaf veins. All pictures taken by Jon Williams, AAFC-Saskatoon.
Third and fourth instar larvae are larger and can consume entire leaves, leaving just the leaf veins. Larvae will also eat the buds, flowers and developing pods. Later in the growing season, as canola matures, diamondback moth larvae can strip the pods of any remaining green tissues.
Damage caused to a canola plant in a colony of diamondback moth maintained at AAFC-Saskatoon. This is an extreme example of the capacity of diamondback moth larvae to strip all green material from the stems, leaving a skeletonized plant with a frosted appearance.The picture also shows how frass (fecal material) can accumulate on the remaining plant tissues. Picture by Meghan Vankosky, AAFC-Saskatoon.
In addition to feeding damage, frass (or fecal material) excreted by diamondback moth larvae can affect the marketability and the quality of crucifer vegetables like broccoli, cauliflower, cabbage and brussels sprouts by contaminating or staining the developing vegetable heads.
Remember that the diamondback moth can have multiple generations per year and that each generation takes about 18-20 days (but can be shorter or longer depending on temperature). With each generation, there is potential for the population density to grow and exceed economic thresholds. Scout for diamondback moth by examining plants for larvae and estimate the number of larvae per m2 to determine if the population is nearing or has exceeded the economic threshold.
In canola, the economic threshold for diamondback moth larvae is 100-150 larvae/m2 when canola plants are immature and flowering. The threshold is 200-300 larvae/m2 when canola plants are mature.
Also, refer to the diamondback moth pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
The week of May 27, 2024, very mature larvae were retrieved in flixweed in southern Alberta (Barkley, pers.comm. 2024). Thus, a second generation of adult diamondback moth is likely active in southern parts of the prairies.
Pheromone-baited Delta traps housing sticky cards are used to monitor diamondback moth across the Canadian prairies. Research has shown that cumulative counts > 25 moths indicate elevated risk. In those areas, it then becomes important to scout and assess larval densities.
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2024.
Provincial entomologist (Barkley, Tansey, Peru, Gavloski) have kindly provided the following summary for this week: • Alberta – two traps have caught > 25 adult diamondback moths; one trap deployed in the County of Warner (as of June 15, 2024) and one trap deployed in the County of Grande Prairie (as of June 8, 2024). • Saskatchewan – 6 RMs have observed cumulative counts >25 (as of June 6, 2024); traps are located near Regina (RM 129), Macroie (RM 285), Buchanan (RM 304), Laura (RM 315), Delisle (RM 345) and Makwa (RM 428). As of June 6, 2024, the highest cumulative count was 61 moths. • Manitoba – pheromone traps at 20 locations have captured > 25 moths, with cumulative trap catches ranging form 28 to 187. All of the traps with elevated risk are located in the Central, Eastern, South Interlake and North Interlake regions of Manitoba.
Scouting and pest management for diamondback moth depends on in-field counts of larvae per metre2! This means plants need to be pulled and tapped off to assess the number of larvae! Use Figure 1 below to help identify the different stages of diamondback moth.
Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.
Biological and monitoring information for DBM (including tips for scouting and economic thresholds) is posted by Manitoba Agriculture, Saskatchewan Agriculture, and the Prairie Pest Monitoring Network. Also, refer to the diamondback moth pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Pheromone traps used to monitor bertha armyworm are typically set up along canola fields when pupal development reaches 75-80%; the 2024 monitoring season started the week of June 10, 2024.
Use the images below (Fig. 1) to help identify moths from the by-catch that will be retained in the green phermone-baited unitraps.
Figure 1. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2024.
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Last week, Shelley Barkley (Alberta Agriculture and Irrigation) swept a flixweed patch in a ditch and found very mature diamondback moth larvae in southern Alberta. Thus, in some parts of the prairies, the first local generation of diamondback moth is nearing completion.
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts being compiled by provincial pheromone trapping networks across the Canadian prairies in 2024.
Biological and monitoring information for DBM (including tips for scouting and economic thresholds) is posted by Manitoba Agriculture, Saskatchewan Agriculture, and the Prairie Pest Monitoring Network. Also, refer to the diamondback moth pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Pheromone traps used to monitor bertha armyworm are typically set up along canola fields when pupal development reaches 75-80%; the 2024 monitoring season will start soon with traps due to be set up the week of June 10, 2024.
Use the images below (Fig. 1) to help identify moths from the by-catch that will be retained in the green phermone-baited unitraps.
Figure 1. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Two species, the striped and crucifer flea beetles, are the most chronic and economically important insect pests of cruciferous field crops grown across western Canada. Both species are already active so prioritize field scouting in fields of emerging and seedling canola and mustard. All cruciferous crops and plants of any Brassicaceae are similarly attractive and can suffer damage from crucifer (P. cruciferae) and striped flea beetles (P. striolata).
Damage to emerging crops can progress very quickly when flea beetle densities are high, even within the same day! The cotyledon stage of canola is most vulnerable to flea beetle feeding.
Learn more about flea beetle damage in canola by reviewing the Insect of the Week (Wk 2 released May 13, 2024). Review photos of flea beetle feeding damage posted in the Weekly Update (Wk 02 – May 14, 2021) to help assess percent feeding damage and to apply the action threshold of 25 % leaf area of cotyledons. The Canola Council of Canada’sCanola Encyclopedia also features flea beetles along with an excellent visual guide to help estimate feeding damage.
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Earlier this week, Shelley Barkley (Alberta Agriculture and Irrigation) swept a flixweed patch in a ditch and found diamondback moth larvae (Fig. 1) that were nearly ready to pupate! Thus, in some parts of the prairies, the first local generation of diamondback moth is well underway and nearing completion.
Figure 1. Diamondback larvae collected using a sweep-net in flixweed growing near Dunmore AB on May 27, 24. Photo: S. Barkley (Alberta Agriculture and Irrigation).
It’s a busy week in the field, so we do not have a full update on diamondback moth trap captures to share this week. Please check out the Provincial Reports for the most up-to-date information available from the diamondback moth pheromone monitoring program.
Biological and monitoring information for DBM (including tips for scouting and economic thresholds) is posted by Manitoba Agriculture, Saskatchewan Agriculture, and the Prairie Pest Monitoring Network. Also, refer to the diamondback moth pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Based on long-term data for the prairie region, bertha armyworm pupal development should be 30-75% completed by late May in a normal year (Fig. 1).
Figure 1. Long-term average predicted bertha armyworm (Mamestra configurata) pupal development (% completion) across the Canadian prairies as of May 28, 2023. Model runs were conducted using climate normal data.
Pheromone traps used to monitor bertha armyworm are typically set up along canola fields when pupal development reaches 75-80%; the 2024 monitoring season will be starting soon, with traps likely to be set up the week of June 10, 2024.
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Two species, the striped and crucifer flea beetles, are the most chronic and economically important insect pests of cruciferous field crops grown across western Canada. Both species are already active so prioritize field scouting in fields of emerging and seedling canola and mustard. All cruciferous crops and plants of any Brassicaceae are similarly attractive and can suffer damage from crucifer (P. cruciferae) and striped flea beetles (P. striolata).
Damage to emerging crops can progress very quickly when flea beetle densities are high, even within the same day! The cotyledon stage of canola is most vulnerable to flea beetle feeding.
Learn more about flea beetle damage in canola by reviewing the Insect of the Week (Wk 2 released May 13, 2024). Review photos of flea beetle feeding damage posted in the Weekly Update (Wk 02 – May 14, 2021) to help assess percent feeding damage and to apply the action threshold of 25 % leaf area of cotyledons. The Canola Council of Canada’sCanola Encyclopedia also features flea beetles along with an excellent visual guide to help estimate feeding damage.
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.
Spring Pheromone Trap Monitoring of Adult Males: Across the Canadian prairies, spring monitoring is initiated to acquire weekly counts of adult moths attracted to pheromone-baited delta traps deployed in fields. Thank you to the many people who deployed and are weekly checking traps across the BC Peace, Alberta, Saskatchewan, and Manitoba! Weekly trap interceptions are observed to generate cumulative counts.
As the season progresses, cumulative count estimates arising from these pheromone traps are broadly categorized to help producers prioritize and time in-field scouting for larvae. Preliminary data from the initial weeks of monitoring includes:
Alberta – So far, two traps in southern Alberta have caught more than 10 moths, one in Mountain View County and one in Kneehill County. Visit Alberta Agriculture and Irrigation’s ‘live’ reporting map for updates through the 2024 growing season.
Saskatchewan – Dr. James Tansey and Carter Peru (Saskatchewan Ministry of Agriculture) shared that traps near Regina (RM129), Makwa (RM561), and Lumsden (RM189) have caught 20-25 adult diamondback moths. Several traps have also caught more than 25 moths so far this monitoring season, including traps near Laura (RM315), Delisle (RM345), Macroie (RM285), and Buchanan (RM304).
Manitoba – Dr. John Gavloski (Manitoba Agriculture) reported that five diamondback moth traps have now captured more than 25 moths in Manitoba. These traps are located in the Central region (2), Eastern region (1) and North Interlake region (2) of the province. So far, the highest cumulative count in a single trap is 69.
Biological and monitoring information for DBM (including tips for scouting and economic thresholds) is posted by Manitoba Agriculture, Saskatchewan Agriculture, and the Prairie Pest Monitoring Network. Also, refer to the diamondback moth pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Two species, Phyllotreta striolata and P. cruciferae, are the most chronic and economically important insect pests of cruciferous field crops grown across western Canada. Both species are already active so prioritize field scouting in fields of emerging and seedling canola and mustard. All cruciferous crops and plants of any Brassicaceae are similarly attractive and can suffer damage from crucifer and striped flea beetles.
If flea beetle densities are high, seedling damage levels can advance quickly – even within the same day! The cotyledon stage of canola is vulnerable to flea beetle feeding. To learn more about flea beetle damage in canola, review the current Insect of the Week (Wk 2 released May 13, 2024). Review photos of flea beetle feeding damage posted in the Weekly Update (Wk 02 – May 14, 2021) to help assess percent defoliated and to apply the action threshold of 25 % leaf area of cotyledons. The Canola Council of Canada’sCanola Encyclopedia also features flea beetles along with an excellent visual guide to help estimate feeding damage.
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.
Spring Pheromone Trap Monitoring of Adult Males: Across the Canadian prairies, spring monitoring is initiated to acquire weekly counts of adult moths attracted to pheromone-baited delta traps deployed in fields. Thank you to the many people who deployed and are weekly checking traps across the BC Peace, Alberta, Saskatchewan, and Manitoba! Weekly trap interceptions are observed to generate cumulative counts.
As the season progresses, cumulative count estimates arising from these pheromone traps are broadly categorized to help producers prioritize and time in-field scouting for larvae. Preliminary data from the initial weeks of monitoring includes:
Alberta – So far, cumulative trap counts ranged from 0-10 moths with the highest interception rates arising from near Barrhead and Camrose AB. Visit Alberta Agriculture and Irrigation’s ‘live’ reporting map for updates through the 2024 growing season.
Saskatchewan – Dr. James Tansey and Carter Peru (Saskatchewan Ministry of Agriculture) shared results arising the weeks of May 1 and May 8, 2024; cumulative trap catches so far ranged from 0-16 with traps near Navscoy, Lumsden, and Coteau SK reporting the most so far.
Manitoba – Dr. John Gavloski (Manitoba Agriculture) reported that cumulative diamondback moth trap catches ranged from 0-23 for the majority of traps but that two sites reported >25 total moths. One site in the Eastern region has intercepted 33 moths and one trap in the North Interlake region has intercepted 61 moths.
Biological and monitoring information for DBM (including tips for scouting and economic thresholds) is posted by Manitoba Agriculture, Saskatchewan Agriculture, and the Prairie Pest Monitoring Network. Also, refer to the diamondback moth pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
The striped flea beetle and crucifer flea beetle are two of the most important pests of canola (and other Brassicaceae) in western Canada, especially early in the growing season. Adult flea beetles spend the winter sheltered under leaf litter, generally along field margins. In spring, adults disperse into crop fields to eat, mate, and lay eggs. For more information about the biology of flea beetles, click here.
‘Shot hole’ feeding damage caused by flea beetles on the cotyledons and first true leaves of a canola seedling. Picture by Ruwandi Andrahennadi, AAFC-Saskatoon.
Flea beetle feeding damage has a characteristic ‘shot-hole’ appearance on the cotyledons, as pictured above. Flea beetle feeding damage can also be observed on the first true leaves (also with a ‘shot-hole’ appearance) and on the stem and growing point of the seedlings.
A striped flea beetle feeding on the stem of a leaf. Excessive feeding on the stems of young seedlings can cause stems to break or plants to wilt and if severe, could kill the seedlings. Picture by Ruwandi Andrahennadi, AAFC-Saskatoon.
To scout for flea beetles, examine seedlings for the characteristic ‘shot-hole’ feeding, starting at the field margin. Scout often, as flea beetles can move into fields quickly. The action threshold for applying foliar insecticides for flea beetle is met when 25% of the cotyledon area has been eaten. Visit the Canola Council of Canada Canola Encyclopedia for tools to help estimate defoliation by flea beetles.
Flea beetles can also cause damage later in the summer when the new generation of flea beetles emerges and are looking for food before winter. The feeding damage looks the same as the damage in the spring. High densities of flea beetles feeding on plants late in the season can cause plants to ripen prematurely and feeding damage on pods can contribute to yield loss via pod shatter.
Drying and desiccated leaves of rutabaga in late summer at Outlook, Saskatchewan, following a severe infestation of new generation flea beetles. Picture by Meghan Vankosky, AAFC-Saskatoon.
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Spring Pheromone Trap Monitoring of Adult Males: Across the Canadian prairies, spring monitoring is initiated to acquire weekly counts of adult moths attracted to pheromone-baited delta traps deployed in fields. Thank you to the many people who deployed and are weekly checking traps across the BC Peace, Alberta, Saskatchewan, and Manitoba! Weekly trap interceptions are observed to generate cumulative counts.
As the season progresses, cumulative count estimates arising from these pheromone traps are broadly categorized to help producers prioritize and time in-field scouting for larvae. Preliminary data from the initial week of monitoring includes:
Alberta – So far, Shelley Barkley (Alberta Agriculture and Irrigation) reported that low numbers of diamondback moth were captured at a few monitoring locations in southern and eastern Alberta and noted the Alberta Agriculture and Irrigation’s ‘live’ reporting map is active for 2024.
Saskatchewan – Dr. James Tansey (Saskatchewan Ministry of Agriculture) also reported that adult diamondback moth were captured at a few locations in Saskatchewan.
Manitoba – Dr. John Gavloski (Manitoba Agriculture) reported that diamondback moth were observed from 13 traps; 3 traps intercepted 10 or above, but no larger counts yet.
Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.
Biological and monitoring information for DBM (including tips for scouting and economic thresholds) is posted by Manitoba Agriculture, Saskatchewan Agriculture, and the Prairie Pest Monitoring Network. Also, refer to the diamondback moth pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
In summer 2023, diamondback moth development is well ahead of average. Model simulations to July 16, 2023, indicate that the third generation of non-migrant adults (based on early May arrival dates) is currently occurring across the Canadian prairies (Fig. 1).
Figure 1. Predicted number of non-migrant generations of diamondback moth (Plutella xylostella) expected to have occurred across the Canadian prairies as of July 16, 2023.
When we ran the model using long term average weather data (based on climate normals), the model output showed that the second generation of diamondback moth would be occurring at this date in a ‘normal’ year (Fig. 2). Above normal temperatures in 2023 have increased the rate of diamondback moth development, resulting in three generations in the time it usually takes for the development of two generations!
Figure 2. The number of non-migrant generations of diamondback moth (Plutella xylostella) expected to have occurred across the Canadian prairies as of July 16, based on climate normal data.
Some areas of the prairies might be at risk of damage from diamondback moth this summer. Pheromone traps with cumulative counts greater than 25 male moths were located around Cadillac, Rosetown, Makwa, Eatonia, and Swift Current in Saskatchewan, in the Vulcan area in Alberta, and in all regions of Manitoba (data in the July 5 Crop Pest Update). According to the July 19 edition of the Manitoba Crop Pest Update, canola fields in the Plum Coulee, St. Joseph and Dominion City areas of Manitoba had high levels of diamondback moth larvae in the last week. Because diamondback moth can have multiple generations in a single growing season and because the generation time is shorter when temperatures are warm, their populations can build up quickly. Keep scouting for diamondback moth to avoid unpleasant surprises at the end of this summer.
To scout for diamondback moth, estimate the number of diamondback moth larvae per m2 at several locations in a field. The economic threshold for diamondback moth is NOT based on pheromone traps or sweep net samples, but on the density of larvae per plant. For immature and flowering canola, the economic threshold is 100-150 larvae/m2. In podded canola, the economic threshold is 200-300 larvae/m2. See the Field Crop and Forage Pests guide and monitoring protocol for more information about scouting for diamondback moth.
Model simulations were used to estimate the status of grasshopper development as of July 9, 2023. As a result of warmer than normal temperatures, grasshopper development continues to be well ahead of average. As of July 9. 2023, the average predicted instar for grasshopper populations across the prairies is 4.9, which is significantly greater than the long term average of 3.1 for this time of year. Simulations indicate that 70% of the prairie population should be in the fifth instar or adult stage (Fig. 1).
Figure 1. Predicted grasshopper (Melanoplus sanguinipes) development, presented as average instar, across the Canadian prairies as of July 9, 2023.
In a ‘normal’ year, we would expect that 57% of the grasshopper population would be in the third or fourth instar in early July (Fig. 2).
Figure 2. In an average year (based on 30-year average weather or climate normals), we expect that about 57% of the grasshopper population would be in the third or fourth instar in early July, as pictured here on the map. In contrast, in 2023, warm weather has significantly sped up the rate of grasshopper development (Fig. 1).
Reports from across the prairies indicate that adult grasshoppers are now occurring. This is much earlier than normal, but agrees with our model simulations, which predict that adult grasshoppers are now occurring across most of the prairies (Fig. 3). Based on earlier than normal appearance of adults, high densities and drought conditions, grasshopper risk may be significant for large areas of Alberta and Saskatchewan as well as southern Manitoba.
Figure 3. The proportion (%) of the migratory grasshopper (Melanoplus sanguinipes) population expected to be in the adult stage across the Canadian prairies as of July 9, 2023.
Models and geospatial maps are tools to help time in-field scouting on a regional scale but grasshopper development and population densities can vary even between relatively close locations. Thus, grasshopper populations are best assessed through scouting. Monitor roadsides and field margins to assess the developmental stage and densities of local grasshopper populations.
Diamondback moths are a migratory invasive species; in 2023, the first migratory adults were found in pheromone traps in early May. Thanks to the above average warm weather across most of the prairie region this year, diamondback moth development is well ahead of average. Based on development models and weather to July 2, a third generation of non-migrant adults is expected to be occurring in some parts of the prairies (Fig. 1), with the second generation occurring in nearly all other areas of the prairies (Fig. 1).
Figure 1. Predicted number of non-migrant generations of diamondback moth (Plutella xylostella) expected to have occurred across the Canadian prairies as of July 2, 2023.
Diamondback moth typically have 4 full generations during prairie summers. In an average year, we would expect that the second generation of non-migrant diamondback moth would we widespread right now, NOT the third non-migrant generation (Fig. 2).
Figure 2. Number of non-migrant generations of diamondback moth (Plutella xylostella) expected to have occurred across the prairie region by early July in a ‘normal’ year (based on 30-year average or long-term normal weather data).
Some areas of the prairies might be at risk of damage from diamondback moth. Pheromone traps with cumulative counts greater than 25 male moths so far in 2023 are located around Cadillac, Rosetown, Makwa, Eatonia, and Swift Current in Saskatchewan, in the Vulcan area in Alberta, and in all regions of Manitoba (see the July 5 Manitoba Crop Pest Update). In Manitoba, the highest counts of diamondback moths in pheromone traps exceed 200 total moths in the Central and Eastern regions. Because diamondback moth can have multiple generations in a single growing season and because the generation time is shorter when temperatures are warm, their populations can build up quickly. Keep scouting for diamondback moth to avoid unpleasant surprises later this summer.
To scout for diamondback moth, estimate the number of diamondback moth larvae per m2 at several locations in a field. The economic threshold for diamondback moth is NOT based on pheromone traps or sweep net samples, but on the density of larvae per plant. For immature and flowering canola, the economic threshold is 100-150 larvae/m2. In podded canola, the economic threshold is 200-300 larvae/m2. See the Field Crop and Forage Pests guide and monitoring protocol for more information about scouting for diamondback moth.
Based on model simulations, bertha armyworm development continues to be 7-10 days ahead of normal. Where present, populations of bertha armyworm will largely be in the larval stage (Fig. 1).
Figure 1. The proportion (%) of the bertha armyworm (Mamestra configurata) population that is expected to be in the larval stage across the Canadian prairies as of July 2, 2023. Note that bertha armyworm may not be present at all locations.
The larvae of this generalist moth could be found in canola fields, but also in other crops.
The lifestages of bertha armyworm: A) eggs, B) larva, C) pupa, and D) adult. All pictures taken by Jonathon Williams, AAFC-Saskatoon (please include a photo credit if these pictures are reproduced elsewhere).
The network of pheromone traps across the prairies is reporting low numbers of adults (less than 300 cumulative catch over the last 6 weeks) so far in 2023, including in Manitoba (check out the July 5 Manitoba Crop Pest Update), Saskatchewan, and Alberta. Only one monitoring location (in Manitoba) has caught more than 300 bertha armyworm adults so far this year, suggesting relatively low risk across the prairies. Risk to yield from bertha armyworm increases when cumulative trap catches exceed 300 (300-900 = medium risk, >900 = high risk). Although the pheromone trap network suggests low risk of economic damage from bertha armyworm, it is still important to scout for larvae. For information about scouting, check out the PPMN protocol and the Alberta Agriculture and Irrigation pages.
Based on model simulations, bertha armyworm development continues to be 7-10 days ahead of normal. Where present, females should have already begun to lay eggs (Fig. 1).
Figure 1. Proportion (% of total population) of the bertha armyworm (Mamestra configurata) population that is expected to be in the egg stage across the Canadian prairies as of June 18, 2023.
In some areas, first instar larvae (caterpillars) may be present (Fig. 2).
Figure 2. Proportion (% of total population) of the bertha armyworm (Mamestra configurata) population that is expected to be in the larval stage across the Canadian prairies as of June 18, 2023.
This week there have been some reports of large green caterpillars on canola crops in Alberta and Saskatchewan. The green caterpillars are too advanced in their development to be bertha armyworm. These are more likely to be alfalfa looper or clover cutworm. This week, a Canola Watch quiz challenges us to identify ‘green worms‘ in oilseed crops and provides excellent information about how to tell the difference between bertha armyworm, alfalfa looper, diamondback moth, clover cutworm, and cabbageworm.
Diamondback moths (Plutella xylostella) are a migratory invasive species; after initial migration into the prairies, diamondback moths can have multiple non-migratory generations during the growing season. Diamondback moth development can be rapid during periods of warm weather. Model simulationsto June 4, 2023, indicate that the first generation of non-migrant adults (based on early-May arrival dates) is currently occurring across the Canadian prairies. If above-normal temperatures persist, then we may start to see some second-generation diamondback moths next week.
The life cycle of diamondback moth can rapidly progress from egg (A) to larvae (B and C), to pupae (D) to adults (E). Photo credit: Jonathon Williams, AAFC-Saskatoon.
On the prairies, we use a network of pheromone traps to detect the first spring appearance of diamondback moths. Now, local scouting is needed to determine if diamondback moth pose a threat to crops. To scout, estimate the number of diamondback moth larvae per m2 at several locations in a field. The economic threshold for diamondback moth is NOT based on pheromone traps or sweep net samples, but on the density of larvae per plant. For immature and flowering canola, the economic threshold is 100-150 larvae/m2. In podded canola, the economic threshold is 200-300 larvae/m2. See the Field Crop and Forage Pests guide and monitoring protocol for more information about scouting for diamondback moth.
Based on model simulations, development of overwintered bertha armyworm (Mamestra configurata) pupae continues to be significantly ahead of normal for most of the prairies. Bertha armyworm pupae across the prairie region are expected to be at least 90% finished their larval development (Fig. 1); as a result, adults might already be emerging in some areas.
Figure 1. Predicted bertha armyworm (Mamestra configurata) pupal development (%) across the Canadian prairies as of June 4, 2023.
The bertha armyworm model predicts that adults could already be present in a region between Lethbridge, Alberta and Swift Current, Saskatchewan (Fig. 2). Adult moths may also be flying near Edmonton, Alberta and in the northern limits of the Peace River region (Fig. 2).
Figure 2. The proportion of the bertha armyworm (Mamestra configurata) population that is predicted to be in the adult stage (% of total population) across the Canadian prairies as of June 4, 2023.
AMANDA JORGENSEN, SHELBY DUFTON, JENNIFER OTANI, AND MEGHAN VANKOSKY*
The 2023 Insect of the Week season kicks off by featuring these small yet economically important beetles. Flea beetles have already been spotted across the prairies. Growers need to be wary of flea beetles even in the initial 7 days following seeding of their host crops, including canola. The best defense is in-field scouting from germination until the first true leaves unfurl and enlarge in size beyond the cotyledon leaf area. The adults create shot-hole damage visible on the topsides of the highly vulnerable cotyledons of canola but careful scouting also involves checking for feeding damage on the undersides of cotyledons and tiny canola stems where they also can feed.
Crucifer Beetle on Canola Leaf — photo credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Several species of flea beetles are present across the Canadian prairies and not all are considered pests. Historically, crucifer (Phyllotreta crucifer), striped (Phyllotreta striolata), and hops (Psylliodes punctulata) flea beetle species have caused damage in canola. Over the past decade, the bluish-black crucifer and black-with-yellow-lined striped flea beetles have proven to be consistent economic pests in canola grown across the Canadian prairies.
Striped and crucifer flea beetles feed on canola, mustard and related cruciferous plants and weeds. Canola is highly susceptible to feeding damage at the cotyledon stage – damage appears as ‘shot-holes’ in cotyledon leaves. Flea beetles also feed on stems and very young seedlings may wilt or break off under windy or damp conditions. New generation adults feed on maturing pods late in the summer. Remember, the Action Threshold for flea beetles on canola is when 25% of cotyledon leaf area is consumed.
*Information here was compiled from past PPMN Insect of the Week feature articles about flea beetles.
Key links for more information and to aid in field scouting include:
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Recent warm conditions have resulted in the rapid development of diamondback moth populations. Model simulations to August 14, 2022, indicate that the fourth generation of non-migrant adults (based on mid-May arrival dates) are currently occurring across the southern prairies (Fig. 1). DBM development is predicted to be marginally greater in 2022 than expected based on long-term average values (Fig. 2).
Warm conditions during August resulted in rapid development of diamondback moth populations. Model simulations to August 21, 2022, indicate that the fourth generation of non-migrant adults (based on mid-May arrival dates) are currently occurring across most of the prairies (Fig. 1). DBM development is predicted to be marginally greater than long-term average values (Fig. 2).
Figure 1. Predicted number of non-migrant generations of diamondback moth (Plutella xylostella) expected to have occurred across the Canadian prairies as of August 21, 2022. Figure 2. Long-term predicted number of non-migrant generations of diamondback moth (Plutella xylostella) expected to have occurred across the Canadian prairies as of August 21, based on climate normal data.
In-Field Monitoring:Remove plants in an area measuring 0.1 m² (about 12″ square), beat them onto a clean surface and count the number of larvae (Fig. 3) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
Figure 3. Diamondback larva measuring ~8mm long. Note brown head capsule and forked appearance of prolegs on posterior.
The economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1 m² (approximately 2-3 larvae per plant). Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1 m² (approximately 1-2 larvae per plant).
Figure 4. Diamondback moth pupa within silken cocoon.
