2023 WEEK 7 (RELEASED JUNE 22, 2023)

Meghan Vankosky
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Week 7

It’s officially summer!

Grasshoppers thrive in warm, dry conditions. The first adult two-striped grasshoppers of 2023 were reported in southern Alberta and Saskatchewan in the last 5 days, although the majority the grasshopper population are still nymphs. Signs of damage in the roadsides and field edges are being reported. Now is the time to scout for grasshoppers in your fields.  

Diamondback moths develop rapidly when it is warm and their population densities can build up quickly with each generation. Like other insects, bertha armyworm development is also well ahead of schedule. Other green caterpillars, like clover cutworm and alfalfa looper, might also be found in canola crops at this time of year. Correctly identifying green caterpillars is important to ensure the correct economic thresholds (where available) and management tactics are used.

This year could be an interesting year for wheat midge. Some areas have had sufficient rain to trigger the end of diapause and the completion of larval and pupal development, but crop staging is also widely variable. Scouting for wheat midge will be important in the next few weeks.

This week, the Insect of the Week featured the cereal leaf beetle, a pest of cereal crops. Next week, we will feature a very important natural enemy of cereal leaf beetle, the parasitoid Tetrastichus julis.

Remember, insect Monitoring Protocols containing information about in-field scouting as well as information about insect pest biology and identification.

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Questions or problems accessing the contents of this Weekly Update? Please contact Dr. Meghan Vankosky (meghan.vankosky@agr.gc.ca) to get connected to our information. Past Weekly Updates, full of information and helpful links, can be accessed on our Weekly Update page.

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Weather Synopsis

Ross Weiss, Tamara Rounce, Jennifer Otani and Meghan Vankosky
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Week 7

This past week (June 12-18, 2023), the prairie average daily temperature was 1.8°C warmer than normal (Fig. 1). The warmest temperatures were observed across southern Manitoba and Saskatchewan and the coolest temperatures occurred across the Peace River region of British Columbia and Alberta.

Figure 1. Seven-day average temperature (°C) observed across the Canadian prairies for the period of June 12-18, 2023. 

Average temperatures over the past 30 days (May 20 to June 18, 2023) have been 4°C above normal with the warmest temperatures being reported across Manitoba and Saskatchewan (Fig. 2).

Figure 2. 30-day average temperature (°C) across the Canadian prairies for the period of May 20 to June 18, 2023. 

Rainfall events were observed across the prairie region in the last week. The 7-day cumulative rainfall was 80-95mm in a region around Edmonton, Alberta (Fig. 3). Areas west of Edmonton that were evacuated due to forest fires are now flooded.

Figure 3. Seven-day cumulative rainfall (mm) observed across the Canadian prairies for the period of June 12 – 18, 2023. 

The greatest 30-day rainfall totals (90-140mm) were reported from Red Deer to Grande Prairie, Alberta for the period from May 20 to June 18, 2023 (Fig. 4). Rainfall totals continue to be lowest across the southern prairies.  

Figure 4. 30-day cumulative rainfall (mm) observed across the Canadian prairies for the period of May 20 to June 18, 2023. 

Over the past 30 days, different parts of the prairies have been characterized by warm/dry, warm/wet, cool/dry, and cool/wet conditions, as represented in the scatter plot (Fig. 5). Grande Prairie and Lacombe, Alberta have generally been cooler and wetter than most other locations across the prairies, while locations in Manitoba have experienced mostly warm and dry weather so far in 2023.  

Figure 5. Site-specific comparison of 30-day average temperature (°C) and cumulative rainfall (mm) observed across the Canadian prairies for the period of May 20 to June 18, 2023. The red line indicates the average temperature and the blue line represents the average rainfall for the period of May 20 to June 18, 2023. 
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Wind Trajectory Summary

Ross Weiss, Serge Trudel and Meghan Vankosky
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Week 7

‘Reverse trajectories’ refer to air currents that are tracked back in time from specified Canadian locations over a five-day period prior to their arrival date. Of particular interest are those trajectories that, prior to their arrival in Canada, originated over northwestern and southern USA and Mexico, anywhere diamondback moth populations overwinter and adults are actively migrating. If diamondback adults are present in the air currents that originate from these southern locations, the moths may be deposited on the Prairies at sites along the trajectory, depending on the local weather conditions at the time that the trajectories pass over our area (e.g., rain showers, etc.). Reverse trajectories are the best available estimate of the ”true” 3D wind fields at a specific point. They are based on observations, satellite and radiosonde data. 

Mexico, California and Texas: This week (June 14 – 20, 2023), no reverse trajectories originating over Mexico, California, or Texas, were predicted to pass over the prairies. 

Pacific Northwest (Idaho, Oregon, Washington): This week, 90 reverse trajectories were predicted to cross the prairies. The majority of Pacific Northwest reverse trajectories were reported to pass over Alberta and western Saskatchewan (Fig. 1).   

Figure 1. Total number of dates with reverse trajectories originating over the Idaho, Oregon, and Washington that have crossed the prairies between April 1 and June 20, 2023. 

Oklahoma and Texas: This week only one (1) reverse trajectory that originated over Texas and Oklahoma was predicted to pass through the prairies, near Selkirk, Manitoba (Fig. 2). 

Figure 2. The total number of dates with reverse trajectories originating over Oklahoma and Texas that have crossed the prairies between April 1 and June 20, 2023. 

Kansas and Nebraska: This week there were 9 reverse trajectories, originating over Kansas and Nebraska, that were predicted to pass over Saskatchewan and Manitoba (Fig. 3).  

Figure 3. The total number of dates with reverse trajectories originating over Kansas and Nebraska that have crossed the prairies between April 1 and June 20, 2023. 
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Predicted Grasshopper Development

Ross Weiss, Tamara Rounce, Owen Olfert, Jennifer Otani and Meghan Vankosky
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Week 7

Model simulations were used to estimate development of grasshoppers as of June 18, 2023. Warm temperatures continue to promote rapid grasshopper development. Model runs suggest that this spring’s hatch is 99% complete. As of June 18, grasshoppers should range from first to fourth instars. Based on average instar, development is most advanced across the southern prairies where 70% of the population is predicted to be third and fourth instars (Fig. 1). The model indicates that grasshopper development should be most advanced near Morden, Manitoba and Kindersley, Saskatchewan.

Figure 1. Predicted grasshopper (Melanoplus sanguinipes) development, presented as average instar, across the Canadian prairies as of June 18, 2023. 

Entomologists across western Canada are closely watching the grasshopper situation. The first adult two-striped grasshopper was found in southern Alberta on June 15 (first reported on Twitter by Dr. Dan Johnson, University of Lethbridge) and in southern Saskatchewan on June 20 (reported by Taylor Dzikowski and Ross Weiss, both from AAFC-Saskatoon).

An adult two-striped grasshopper, Melanoplus bivittatus. Picture credit: Meghan Vankosky, AAFC-Saskatoon.

Geospatial maps, like that in Fig. 1, are tools to help time in-field scouting on a regional scale. However,  grasshopper development can vary from region to region and from field to field. To best assess local grasshopper development, scouting is required. In Saskatchewan, grasshoppers have already been observed in field crops in some regions and there have been reports of spraying for grasshoppers in some areas. Scout or monitor grasshopper populations in roadsides and field margins to assess the development and densities of local grasshopper populations. 

Information about grasshoppers and grasshopper monitoring is available from the Prairie Pest Monitoring Network, in the Field Crop and Forage Pests guide, Alberta Agriculture and Irrigation, Saskatchewan Ministry of Agriculture, and Manitoba Agriculture. 

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Predicted Diamondback Moth Development

Ross Weiss, Tamara Rounce, Owen Olfert, Jennifer Otani and Meghan Vankosky
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Week 7

Diamondback moths (Plutella xylostella) were first found on pheromone traps across western Canada in early May in 2023. After the first migrant adults arrive, there can be multiple non-migrant populations of diamondback moth, with the population density potentially increasing with each generation. Average development, based on climate normals, suggests that diamondback moths should be in the first non-migrant generation. However, diamondback moth development can be rapid during periods of warm weather, such as we have experienced across most of western Canada so far this spring. As a result, model simulations to June 18, 2023, indicate that prairie diamondback moth populations are now in the second non-migrant generation (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 June 18, 2023. 

Local scouting is needed to determine if diamondback moths 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.

The life stages of diamondback moth: A) eggs, B) early instar larva, C) later instar larva, D) pupa, and E) adult. Picture credit: Jonathon Williams, AAFC-Saskatoon.
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Predicted Bertha Armyworm Development

Ross Weiss, Tamara Rounce, Owen Olfert, Jennifer Otani and Meghan Vankosky
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Week 7

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.

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Predicted Wheat Midge Development

Ross Weiss, Tamara Rounce, Owen Olfert, Jennifer Otani and Meghan Vankosky
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Week 7

Wheat midge (Sitodiplosis mosellana) overwinter as larval cocoons in the soil. Soil moisture conditions in May and June largely determine whether or not larvae exit cocoons to move to the soil surface to continue development (i.e., to pupate then emerge as adults this season). 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. Wheat midge emergence may be delayed or erratic if rainfall does not exceed 20-30 mm during May and June.

Cumulative rainfall from May 1-June 18, 2023 across western Manitoba, most of Saskatchewan, and northwestern Alberta now exceeds the threshold (30 mm) required to terminate larval diapause. Though late, the rainfall event last week in the Edmonton region of Alberta may promote movement of larvae to the soil surface.

The wheat midge model indicates that, where wheat midge populations are present, larvae have begun to move to the soil surface (Fig. 1).

Figure 1. Proportion (%) of the larval population of wheat midge (Sitodiplosis mosellana) that is expected to have moved to the soil surface across western Canada, as of June 18, 2023. 

Pupae are expected to be in the soil in the Peace River region, localized areas of Saskatchewan, and southwestern Manitoba (Fig. 2).

Figure 2. Proportion (%) of the wheat midge (Sitodiplosis mosellana) population that is predicted to be in the pupal stage in western Canada, as of June 18, 2023. 

Model output suggests that first adults may be appearing in fields in southeastern Saskatchewan and southwestern Manitoba this week. Dr. Tyler Wist reports that adult wheat midge have been found on sticky cards baited with pheromone lures, including at the AAFC research farm in Saskatoon.

Scouting for adult wheat midge should start now. Over the next few weeks, the Prairie Pest Monitoring Network will continue to use phenology models to predict the status of wheat midge development and will provide additional updates.

For information about scouting, check out the wheat midge monitoring protocol. More information is available from Alberta Agriculture and Irrigation, the Saskatchewan Ministry of Agriculture, and Field Crop and Forage Pests and their Natural Enemies in Western Canada available for free download from our Field Guides page.

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Provincial Insect Updates

John Gavloski, James Tansey, Shelley Barkley and Meghan Vankosky
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Week 7

Visit the Alberta Insect Pest Monitoring Network and Crop Insects pages for information about insects and monitoring in Alberta, including links for live maps from the 2023 monitoring season for diamondback moth, bertha armyworm, cutworms and others.

New issues of the Saskatchewan Crop Production News are coming soon in 2023. Use the link to browse the articles from 2022 or subscribe to receive new issues of the newsletter as they are published online.

Weekly Manitoba Crop Pest Updates for 2023 are available online with timely updates about insect pests, weeds, and plant pathogens. Watch their website for new Crop Pest Updates (usually published on Wednesdays this year).

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CEREAL LEAF BEETLE

Shelby Dufton, Amanda Jorgensen, Jennifer Otani and Meghan Vankosky
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Week 7

The cereal leaf beetle (Oulema melanopus) is an invasive insect pest that feeds on oat, barley, corn, rye, triticale, reed canary grass, ryegrass, fescue, wild oat, and millet, though wheat is their preferred host. Originally from Europe, it is now found in most cereal production areas in North America. The cereal leaf beetle can be found in parts of Manitoba, Saskatchewan, and Alberta. 

Adult cereal leaf beetle. Photo credit: Boris Loboda.

Adult cereal leaf beetles are about 6 mm long and bear striking coloration with an orange-red thorax, yellow-orange legs, and a metallic blue head and wing covers. Adults overwinter in field debris in the fall, typically emerging in mid-April to May in the Canadian prairies to feed and lay their eggs. Cereal leaf beetle eggs are laid singly or in clusters of two or three along upper leaf surfaces, close to the margins or mid-rib. Initially appearing bright yellow, eggs darken to orange-brown and then black before hatching. 

Cereal leaf beetle larva. Photo credit: Dr. John Gavloski

Larvae are the most damaging stage of this insect, feeding on upper leaf surfaces. Larval damage appears in pale lines similar in appearance to window-panes. Severe damage is similar to frost damage, where the leaves appear white and can also be mistaken for slug damage. Larvae are yellow in color with a brown head but may appear black like an oil droplet. Black coloration results from a defense mechanism, where larvae smear themselves with a fecal coating to mask their vibrant coloration and reduce predation. After feeding for 10 to 14 days, larvae drop to the soil, entering a pre-pupal and then pupal stage. Larvae pupate below the soil near the host plant’s roots for three weeks, after which they emerge as adults to feed and move to overwintering sites. 

Cereal leaf beetle damage to a cereal crop. Photo credit: Bob Hammon, Colorado State University, bugwood.org

Monitoring for this pest should first occur in the spring, when producers should be on the lookout for adults emerging to feed. Scouting continues throughout the spring and summer, before and during the boot stage to assess cereal leaf beetle populations. Egg and larval scouting should be conducted at 5 to 10 random sites throughout the field, at least three meters from the edge. 10 consecutive plants should be inspected at each location, with the number of eggs and larvae counted per plant (before tillering) or per stem (after tillering). Following this, the average number of eggs and larvae is calculated per plant. Economic thresholds have not been established in Canada but have been established for Montana and North Dakota.  

Tune in next week to learn about the cereal leaf beetle’s natural enemy – Tetrastichus julis! 

Biological and monitoring information related to cereal leaf beetle in field crops is available online. For more information, visit the cereal leaf beetle page from the Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management field guide. (en français : Guide d’identification des ravageurs des grandes cultures et des cultures fourragères et de leurs ennemis naturels et mesures de lutte applicables à l’Ouest canadien). 

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