Week 9 and the unusually hot weather stretching over the Canadian prairies is making it difficult for plants to tolerate insect pest pressure! Scouting is critical under these conditions! Be sure to catch the Insect of the Week – it’s lygus bugs! This week find updates to predictive model outputs for wheat midge, grasshoppers, bertha armyworm, and diamondback moth plus a lot more to help prepare for in-field scouting!
Stay safe and good scouting to you!
Questions or problems accessing the contents of this Weekly Update? Please contact us so we can connect you to our information. Past “Weekly Updates” can be accessed on our Weekly Update page.
TEMPERATURE: This past week (June 21-27, 2021), weekly temperatures were warmer than normal and rainfall amounts were generally less than 5 mm. The warmest temperatures were observed across Alberta (Fig. 1).
Across the prairies, the average 30-day (May 29 – June 27) temperature was almost 3 °C warmer than climate normal values. The warmest temperatures continue to be observed across southern Manitoba and southeastern Saskatchewan (Fig. 2). The 2021 growing season (April 1 – June 27, 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 central Alberta, southeastern Saskatchewan and southwestern Manitoba. Minimal rainfall was reported across most of central Alberta and northwestern Saskatchewan (Fig. 4).
Rainfall amounts for the period of May 29-June 27 (30-day accumulation) were near normal. Rainfall amounts have been below normal across Alberta and large areas of Saskatchewan. Eastern Saskatchewan and western Manitoba have continued to receive the greatest amount of rainfall (Fig. 4).
Average growing season (April 1 – June 27) precipitation was 103 % of normal with greatest precipitation occurring across eastern Saskatchewan, including Regina. Below normal rainfall has been reported across western Saskatchewan, southern Alberta and the Peace River region (Fig. 6).
Access background information for how and why wind trajectories are monitored in this post.
1. REVERSE TRAJECTORIES (RT) Since June 16, 2021, a decreasing number of reverse trajectories have moved north from the Pacific Northwest (Idaho, Oregon and Washington), Texas, Oklahoma, Kansas and Nebraska (Fig. 1). Though these US regions can be a source of diamondback moths (DBM), the ECCC models predict air movement, not actual occurrence of diamondback moths. Fields (and DBM traps) should be monitored for DBM adults and larvae.
a. Pacific Northwest (Idaho, Oregon, Washington) – This week (June 22-28, 2021) there were 3 trajectories that crossed Alberta, Manitoba and Saskatchewan that originated in the Pacific Northwest.
b. Mexico and southwest USA (Texas, California) – This week (June 22-28, 2021) there were 0 trajectories that originated in Mexico or the southwest USA that crossed the prairies.
c. Oklahoma and Texas – This week (June 22-28, 2021) there were 0 trajectories originating in Oklahoma or Texas that passed over the prairies.
d. Kansas and Nebraska – This week (June 22-28, 2021) there were 0 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. 2). 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
This week, wheat midge model simulations indicate that the majority of the larval population has moved to the soil surface (Figure 1). Dry conditions in the Peace River region have resulted in delayed development of larval cocoon populations. Pupae should now be occurring across most of the prairies (Figure 2). First appearance of adults is predicted across Manitoba and most of Saskatchewan (Figure 3).
The model was projected to July 13 to determine potential development at Regina (Fig. 4), Lacombe (Fig. 5), and Grande Prairie (Fig. 6) over the next two weeks.
Compared to Lacombe and Grande Prairie, Regina has been warmer and wetter for the period of May 1 – June 27, 2021, resulting in advanced development of larvae and pupae (Fig. 4). In the Regina and Lacombe areas, initial oviposition is predicted to occur this week (Figs. 4 and 5). Emergence patterns for southern Manitoba are predicted to be similar to Regina. Cooler and dryer conditions in the Peace River region are expected to have impacted the movement of larvae to the soil surface, resulting in reduced adult emergence and later appearance of adults. Oviposition in the southern Peace River region is predicted to occur during the first week of July (Figure 6). Wheat crops near all three locations may be susceptible for the next 14-17 days.
If not already underway, scouting for wheat midge adults should begin this week and especially in regions where higher densities are predicted to occur. It is especially important to be monitoring for adults at dusk in regions expected to be at high risk, based on the 2020 survey which is mapped here.
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 were 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 27, 2021. The development of grasshopper nymphs, based on average instar, should be most advanced across southern Manitoba and southeastern Saskatchewan (Figure 1). Grasshopper populations south of Winnipeg are predicted to be mostly in the 4th and 5th instar stages. Across the prairies, nymph development, as of June 27, 2021 is well ahead of long term average values (Figure 2).
The model was projected to July 13 to determine potential development at Saskatoon and Grande Prairie over the next two weeks. Results suggest that by July 13, Saskatoon populations will primarily be in the fourth and fifth instars with first appearance of adults (Figure 3). Development near Grande Prairie is predicted to be slower, with populations being mostly in the third and fourth instars (Figure 4). 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:
Model simulations to June 27, 2021 indicate that development of bertha armyworm (BAW) (Mamestra configurata) populations is transitioning to egg and larval stages. Model simulations indicate that BAW oviposition is occurring across most of the prairies with occurrence of larvae across southern regions of all three provinces (Figs. 1 and 2).
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. Model projections to July 13 predict that development near Brandon will be more advanced than development near Lacombe (Figs. 3 and 4). Over the next few days adult populations should be declining in southern Manitoba. In central Alberta adults should continue to lay eggs over the next 10 days. Above average temperatures will result in rapid development of larval populations.
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.
Monitoring is already underway for cabbage seedpod weevil (CSPW; Ceutorhynchus obstrictus) in southern areas of the prairies – it was the Insect of the Week for Wk08! There is one generation of CSPW per year and 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.
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. The Insect of the Week featured lygus bugs for Wk 09 – be sure to take a look!
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.
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 27, 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 and southeastern Saskatchewan (Figure 1).
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).
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:
The following is offered to help predict when Culex tarsalis, the vector for West Nile Virus, will begin to fly across the Canadian prairies (Fig. 1). This week, regions most advanced in degree-day accumulations for Culex tarsalis are shown in Figure 1 but the current unusual heat across the prairies will accelerate mosquito development! As of June 27, 2021 (Fig. 1), C. tarsalis development is most advanced in Manitoba and within small pockets in southeastern Alberta. Stay tuned because this map will change quickly to yellow and more imminently orange then red (i.e., areas with sufficient heat accumulation for C. tarsalis to emerge). Prepare yourself by having DEET on hand for the weeks to come!
Anyone keen to identify mosquitoes will enjoy this pictorial key for both larvae and adults which is posted on the Centre for Disease Control (CDC) website but sadly lacks a formal citation other than “MOSQUITOES: CHARACTERISTICS OF ANOPHELINES AND CULICINES prepared by Kent S. Littig and Chester J. Stojanovich” and includes Pages 134-150. The proper citation may be Stojanovich, Chester J. & Louisiana Mosquito Control Association. (1982). Mosquito control training manual. pp 152.
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 01Jul2021) but follow the hyperlink to check the interactive map. They’ve reached more sites in Manitoba and Saskatchewan compared to last week!
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 30, 2021 report here. Be sure to bookmark their Crop Pest Update Index to readily access these reports! 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. 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 65 traps intercepted moths and the highest cumulative count was 171 moths near Selkirk. Access the summary (as of June 30, 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 are available so refer to the Live Map. • Cabbage seedpod weevil sweep-net monitoring update for AB – In-field counts can be entered here to populate 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 has drawn to a close for 2021. Refer to the Live Map which reports extremely low numbers of moths intercepted so far (<50 province-wide as of 01Jl2021). At this point, in-field scouting for larvae remains important. • Cutworm reporting tool – Refer to the Live Map which now reports seven sites with cutworms (as of 01Jul2021).
On the Canadian prairies, there are several native lygus bug species that cause crop damage including Lygus borealis, L. keltoni, pale legume bug (L. elisus), tarnished plant bug (L. lineolaris) and western tarnished plant bug (L. hesperus). The species vary by preferred host plants, region, and seasonally. These insects feed on both cultivated and wild plants such as canola, alfalfa, soybeans, sunflowers, other crop plants and weeds.
Adult and nymph lygus bugs have mouthparts that allow them to pierce and suck liquids out of their plant hosts. Their desired meal usually includes new growth and reproductive parts such as buds, flowers and young seeds. Having punctured the plant, lygus bugs will inject digestive enzymes and suck out the plant juices. Crop damage includes buds and flowers falling off, incomplete seed pod maturation, misshapen fruit and seeds that collapse and shrink.
Adult lygus bugs are 6 millimetres (1/4 inch) long and vary in colour, ranging between pale green to reddish, brown to black, and uniform to mottled. A distinct triangular or V-shaped marking on the upper centre of their backs and wingtips is also present and can be used to distinguish them from other Hemiptera. Mature nymphs share similar colouration to adults, but with five black dots on their thorax and abdomen.