Week 8 and several days of unusually warm weather are going to make field scouting even more important! Be sure to catch the Insect of the Week – it’s cabbage seedpod weevil! This week find updates to predictive model outputs for grasshoppers, wheat midge, bertha armyworm, and diamondback moth plus a lot more to help prepare for in-field scouting!
Stay safe and good scouting to you!
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TEMPERATURE: This past week (June 14-20, 2021), weekly temperatures were above normal and rainfall amounts for Saskatchewan and Manitoba were less than 5 mm. The warmest temperatures were observed across the southern and central regions of Alberta as well as western Saskatchewan (Fig. 1).
Across the prairies, the average 30-day (May 22 – June 20) temperature was 1.4 °C warmer than climate normal values. The warmest temperatures were observed across southern Manitoba (Fig. 2). The 2021 growing season (April 1 – June 20, 2021) has been characterized by near normal temperatures. The warmest temperatures have occurred across southern and central regions of the three prairie provinces (Fig. 3).
PRECIPITATION: This week, the highest rainfall amounts were reported across the Peace River region. Minimal rainfall was reported across most of Manitoba (Fig. 4). Rainfall amounts for the period of May 22-June 20 (30-day accumulation) were above normal (150 % of long-term average values). Rainfall amounts have been above normal for northeastern Alberta, most of Saskatchewan, and western and central regions of Manitoba (Fig. 5).
The average growing season (April 1 – June 20) precipitation was 116 % of normal with the greatest precipitation occurring across central Alberta, eastern Saskatchewan, including Regina, and an area extending from Brandon to Winnipeg. Below normal rainfall has been reported across western Saskatchewan and southern Alberta (Fig. 6).
Access background information for how and why wind trajectories are monitored in this post.
1. REVERSE TRAJECTORIES (RT) Since June 16, 2021, there have been a decreasing number of reverse trajectories that moved north from the Pacific Northwest (Idaho, Oregon and Washington), Texas, Oklahoma, Kansas and Nebraska (Fig. 1).
a. Pacific Northwest (Idaho, Oregon, Washington) – This week (June 16-21, 2021) there have been 43 trajectories that have crossed Alberta, Manitoba and Saskatchewan that originated in the Pacific Northwest (Fig. 2).
b. Mexico and southwest USA (Texas, California) – This week (June 16 – 21, 2021) there have been 3 trajectories that originated in Mexico or the southwest USA that have crossed the prairies.
c. Oklahoma and Texas – This week (June 16 – 21, 2021) there have been 4 trajectories originating in Oklahoma or Texas that have passed over the prairies.
d. Kansas and Nebraska – This week (June 16 – 21, 2021) there have been 8 trajectories that originated in Kansas or Nebraska that passed over the prairies.
2. FORWARD TRAJECTORIES (FT) a. Since June 9, 2021, there has been a steady decrease in the number of forward trajectories that are predicted to cross the prairies (Fig. 3). The dates on the graph report when the trajectories originated in the USA (blue bars). These trajectories generally require 3-5 days to enter the prairies (red line).
Wheat midge (Sitodiplosis mosellana) overwinter as larval cocoons in the soil. Soil moisture conditions in May and June can have significant impacts on wheat midge emergence. Adequate rainfall promotes termination of diapause and movement of larvae to the soil surface where pupation occurs. Insufficient rainfall in May and June can result in delayed movement of larvae to the soil surface. Elliott et al. (2009) reported that wheat midge emergence was delayed or erratic if rainfall did not exceed 20-30 mm during May. Olfert et al. (2016) ran model simulations to demonstrate how rainfall impacts wheat midge population density. The Olfert et al. (2020) model indicated that dry conditions may result in: a. Delayed adult emergence and oviposition b. Reduced numbers of adults and eggs
Wheat midge model simulations indicate that the majority of the larval population has moved to the soil surface (Fig. 1). Dry conditions in the Peace River region have resulted in delayed development of larval cocoon populations. First appearance of pupae should be occurring near Winnipeg, Brandon, Regina and Edmonton areas (Fig. 2).
The model was projected to July 6 to determine potential development at Regina, Lacombe and Grande Prairie over the next two weeks. Compared to Lacombe and Grande Prairie, Regina has been warmer and wetter for the period of May 1 – June 20, 2021 (Fig.3). The first appearance of adults in the Regina area is expected to occur this week and initial oviposition is predicted to occur by the end of June. Emergence patterns for southern Manitoba are predicted to be similar to Regina.
Cooler temperatures at Lacombe are predicted to result in slower development of larvae and pupae (relative to Regina) with the first emergence of adults predicted to occur during the last week of June (Fig. 4). Cooler and dryer conditions in the Peace River region will impact the movement of larvae to the soil surface, resulting in reduced adult emergence and later appearance of adults; adult emergence is predicted to occur during the first week of July (Fig. 5).
Based on predictions for adult emergence, monitoring for the appearance of wheat midge adults should begin this week in Manitoba and Saskatchewan and later next week across Alberta in areas where wheat midge is expected to occur. It is especially important that adult monitoring be prioritized in regions with high risk based on the 2020 survey (Fig. 6).
Monitoring:When scouting wheat fields, pay attention to the synchrony between flying midge and anthesis.
In-field monitoring for wheat midge should be carried out in the evening (preferably after 8:30 pm or later) when the female midges are most active. On warm (at least 15 ºC), calm evenings, the midge can be observed in the field, laying their eggs on the wheat heads (Fig. 7). Midge populations can be estimated by counting the number of adults present on 4 or 5 wheat heads. Inspect the field daily in at least 3 or 4 locations during the evening.
REMEMBER that in-field counts of wheat midge per head remain the basis of the economic threshold decision. Also remember that the parasitoid, Macroglenes penetrans (Fig. 8), is actively searching for wheat midge at the same time. Preserve this parasitoid whenever possible and remember insecticide control options for wheat midge also kill these beneficial insects who help reduce midge populations.
Economic Thresholds for Wheat Midge: a) To maintain optimum No. 1 grade: 1 adult midge per 8 to 10 wheat heads during the susceptible stage. b) To maintain yield only: 1 adult midge per 4 to 5 heads. At this level of infestation, wheat yields will be reduced by approximately 15% if the midge is not controlled. Inspect the developing kernels for the presence of larvae and larval damage.
Wheat midge was featured as the Insect of the Week in 2021 (for Wk07). Be sure to also review wheat midge and its doppelganger, the lauxanid fly, featured as the Insect of the Week in 2019 (for Wk11) – find descriptions and photos to help with in-field scouting! Additionally, the differences between midges and parasitoid wasps was featured as the Insect of the Week in 2019 (for Wk12). Remember – not all flying insects are mosquitoes nor are they pests! Many are important parasitoid wasps that actually regulate insect pest species in our field crops OR pollinators that perform valuable ecosystem services!
More information about wheat midge can be found by accessing the pages from the new “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide”. View ONLY the Wheat midge pages but remember the guide is available as a free downloadable document as both an English-enhanced or French-enhanced version.
Model simulations were used to estimate grasshopper (Melanoplus sanguinipes) development as of June 20, 2021. As of June 20, hatch is predicted to be underway across most of the prairies with a prairie average of 69 % (versus 45 % last week). Percent hatch was greater than 90 % across most of Manitoba, Saskatchewan, and southern Alberta. Development in the central and Peace River regions of Alberta has been significantly slower than the rest of the prairies (Fig. 1).
Development of grasshopper nymphs, based on average instar, should be greatest across southern Manitoba and southern Saskatchewan (Fig. 2). Grasshopper populations south of Winnipeg are predicted to be mostly in the 3rd and 4th instar stages. Across the prairies, nymph development, as of June 20, 2021, is well ahead of long-term average values across most of the prairies (Fig. 3).
The model was projected to July 6 to determine potential development at Winnipeg and Lethbridge over the next two weeks. Results suggest that by July 6, Winnipeg populations will primarily be in the fourth and fifth instars with the first appearance of adults (Fig. 4). Development near Lethbridge is predicted to be slower, with populations being mostly in the third and fourth instars (Fig. 5). Producers are advised to monitor roadsides and field margins to assess the development and densities of local grasshopper populations.
Grasshopper Scouting Steps: ● Review grasshopper diversity and scouting information including photos of both nymphs, adults and non-grasshopper species to aid in-field scouting and accurately apply thresholds for grasshoppers. ● Measure off a distance of 50 m on the level road surface and mark both starting and finishing points using markers or specific posts on the field margin. ● Start at one end in either the field or the roadside and walk toward the other end of the 50 m, making some disturbance with your feet to encourage any grasshoppers to jump. ● Grasshoppers that jump/fly through the field of view within a one-meter width in front of the observer are counted. ● A meter stick can be carried as a visual tool to give perspective for a one-meter width. However, after a few stops, one can often visualize the necessary width and a meter stick may not be required. Also, a hand-held counter can be useful in counting while the observer counts off the required distance. ● At the endpoint, the total number of grasshoppers is divided by 50 to give an average per meter. For 100 m, repeat this procedure. ● Compare counts to the following damage levels associated with pest species of grasshoppers: 0-2 per m² – None to very light damage 2-4 per m² – Very light damage 4-8 per m² – Light damage 8-12 per m² – Action threshold in cereals and canola 12-24 per m² – Severe damage 24 per m² – Very severe damage For lentils at flowering and pod stages, >2 per m² will cause yield loss. For flax at boll stages, >2 per m² will cause yield loss. ● More practically, the following thresholds are offered but, in the event of additional crop stress (e.g., drought), the use of “may be required” versus “control usually required” requires careful consideration:
Scouting for grasshoppers is a priority across the Canadian prairies with nymphs now active in fields from Manitoba to the Peace River region! Several entomologists have kindly offered photos to aid in-field scouting efforts so take these along and use these important points to d more accurately identify grasshopper nymphs and adults:
Traditionally, the economically damaging species of grasshoppers on the Canadian prairies include: • Migratory (Melanoplus sanguinipes; Figs. 1, 2, 3) • Clear-winged (Camnula pellucida; Fig. 3, 4, 5) • Two-striped (Melanoplus bivittatus; Fig. 6, 7, 8) • Packard’s (Melanoplus packardii; Fig. 9) • And more recently Bruner’s grasshopper (Melanoplus bruneri; Fig. 10)
Not everything that hops is a grasshopper! Several species of native slant-faced grasshoppers (normally not causing economic damage; Fig. 11) typically emerge earlier in the spring than economic pest species. Several species of leafhoppers and their closely related froghopper, and treehopper relatives also hop. In fact, early instar grasshopper nymphs are similar in size to leafhopper adults (Fig. 12). Roadside vegetation can be heavily populated by non-damaging leafhoppers and native katydids (Fig. 13) – a sweep-net will allow comparison and improve identification. Katydids resemble grasshoppers in an important way; egg, nymphal instar, and adult stages appear over similar time frames through the growing season.
Monitoring and management of the various pest species of grasshoppers ideally focuses on nymphal instar stages. Compared to adults, early instar grasshopper nymphs are at the beginning of the consumptive portion of life, plus nymphs lack full-sized wings (and have only small wing buds) so they are easier to count and manage. Pest species like the clear-winged grasshopper (C. pellucida) develop through five nymphal instar stages then mature to winged adults.
ECONOMIC THRESHOLDS – The general economic threshold for grasshoppers in cereals is 8-12 per square metre but will vary by crop and growing conditions. – Grasshopper densities exceeding 8-12 per square metre usually warrant control measures. – More specifically, the following thresholds are offered but, in the event of additional crop stress (e.g., drought), the use of “may be required” versus “control usually required” will require careful consideration.
Model simulations to June 20, 2021, indicate that the development of bertha armyworm (BAW) (Mamestra configurata) pupae are nearly complete. Other than the Peace River region, BAW adults should now be active across the prairies (Fig. 1). Model simulations indicate that BAW oviposition has begun across southern areas of Manitoba, Saskatchewan and localized areas in Alberta (Fig. 2).
Model projections to July 6 predict that development near Brandon will be more advanced than development near Grande Prairie (Figs. 3 and 4). BAW populations in southern Manitoba are predicted to be predominantly in the larval stage by early July whereas BAW populations near Grande Prairie will be in the adult and egg stages.
Provincial insect pest monitoring networks in Manitoba, Saskatchewan and Alberta are now compiling cumulative counts of adults intercepted from the pheromone-baited green unitraps deployed in fields across the prairies. Review the Provincial Insect Pest Report Links to find summaries or link to the latest bertha armyworm moth counts by clicking the appropriate province’s reporting info for Manitoba, Saskatchewan or Alberta.
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.
Model simulations to June 20, 2021, indicate that the first generation of non-migrant adults are currently emerging across the Canadian prairies and that the start of the second generation is occurring in southern Manitoba (Fig. 1).
So far, Manitoba, Saskatchewan, Alberta and the BC Peace are all reporting relatively low numbers of intercepted DBM in pheromone traps (read provincial insect pest report links) despite the fact that favourable wind trajectories have passed over the Canadian prairies from southern regions of North America (review wind trajectory reports for 2021). Even so, once DBM are present in an area, it is important to monitor individual canola fields for larvae. Warm growing conditions can quickly translate into multiple generations in a very short time so use the following photos to help identify larvae (Fig. 2), pupae (Fig. 3), or adults (Fig. 4)!
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.
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).
Monitoring is already underway for cabbage seedpod weevil (Ceutorhynchus obstrictus; CSPW) in southern areas of the prairies – it’s the Insect of the Week for Wk08! There is one generation of CSPW per year and the overwintering stage is the adult which is an ash-grey weevil measuring 3-4mm long (Refer to lower left photo). Adults typically overwinter in soil beneath leaf litter within shelter belts and roadside ditches.
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.
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.
Albertan growers can report and check the live map for CSPW posted by Alberta Agriculture and Forestry (screenshot provided below for reference; retrieved24Jun2021).
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. Adults overwinter in northern climates. The economic threshold for Lygus in canola is applied at late flower and early pod stages.
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 continue 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. In fact, sampling is most accurate when repeated at a total of 15 spots within the field. Samples can be taken along or near the field margins. Calculate the cumulative total number of lygus bugs and then consult the sequential sampling chart (Figure 3).
If the total number is below the lower threshold line (Fig. 3), no treatment is needed. If the total is below the upper threshold line, take more samples. If the total is on or above the upper threshold line, calculate the average number of lygus bugs per 10-sweep sample and consult the economic threshold tables (Tables 1 and 2).
The economic threshold for lygus bugs in canola covers the end of the flowering (Table 1) and the early pod ripening stages (Table 2). Once the seeds have ripened to yellow or brown, the cost of controlling lygus bugs may exceed the damage they will cause prior to harvest, so insecticide application is not warranted. Consider the estimated cost of spraying and expected return prior to making a decision to treat a crop.
Remember that insecticide applications at bud stage in canola have not been proven to result in an economic benefit in production. The exception to this is in the Peace River region where early, dry springs and unusually high densities of lygus bug adults can occasionally occur at bud stage. In this situation, high numbers of lygus bugs feeding on moisture-stressed canola at bud stage is suspected to result in delay of flowering so producers in that region must monitor in fields that fail to flower as expected.
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 new “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” – both English or French versions are available.
Track the migration of the Monarch butterflies as they move north by checking the 2021 Monarch Migration Map! A screenshot of the map has been placed below as an example (retrieved 24Jun2021) but follow the hyperlink to check the interactive map. They’ve reached more sites in Saskatchewan and one site in southern Alberta!
Provincial entomologists provide insect pest updates throughout the growing season so link to their information:
MANITOBA’SCrop Pest Updates for 2021 are now available – access the June 23, 2021 report here. Be sure to bookmark their Crop Pest Update Index to readily access these reports! Also, bookmark their insect pest homepage to access fact sheets and more! • Bertha armyworm pheromone trap monitoring update for MB – Cumulative counts arising from weekly data are available here. Happily, the initial counts are very low so far. • Diamondback moth pheromone trap monitoring update for MB – Trapping has drawn to a close for 2021. Access the summary here. Only 59 traps intercepted moths and the highest cumulative count was 142 moths near Selkirk. Access the summary (as of June 22, 2021). At this point, in-field scouting for larvae remains important.
ALBERTA’SInsect Pest Monitoring Network webpage links to insect survey maps, live feed maps, and insect trap set-up videos and more. There is also a Major Crops Insect webpage. The new webpage does not replace the Insect Pest Monitoring Network page. Remember, AAF’s Agri-News occasionally includes insect-related information or Twitter users can connect to #ABBugChat Wednesdays at 10:00 am. • Wheat midge pheromone trap monitoring update for AB – Cumulative counts arising from weekly data will be available shortly so refer to the Live Map. • Bertha armyworm pheromone trap monitoring update for AB – Cumulative counts arising from weekly data have begun so refer to the Live Map. • Diamondback moth pheromone trap monitoring update for AB – Trapping is drawn to a close for 2021. Refer to the Live Map which reports extremely low numbers of moths intercepted so far (<45 province-wide as of 24Jun2021). At this point, in-field scouting for larvae remains important. • Cutworm reporting tool – Refer to the Live Map which still reports only four sites with cutworms (as of 17Jun2021).
First discovered in the Prairie region during the 1990s, the cabbage seedpod weevil is a pest in both its adult and larval stages. Cabbage seedpod weevils emerge from overwintering in the spring as soil temperatures warm, and utilize plants like canola, brown and wild mustard to sustain larval development.
Both adult and larval stages can cause crop damage. As adults, cabbage seedpod weevils can cause canola flower budblasting as they feed on developing flowers, and later in the season their appetites will turn to canola pods. However, it is the cabbage seedpod weevil larvae causes the most damage. During their development, these larvae will bore into seed pods and consume the seeds within. Infested pods are more prone to shattering and are more susceptible to fungal infections.
Adult cabbage seedpod weevils are 3–4 mm long with a long narrow snout. When disturbed, these insects “play dead,” resuming activity when the perceived threat has passed. Mature larvae are 2–3 mm long with a whitish body, brown head and anal plate, and 3 pairs of thoracic legs.