2023 WEEK 6 (Released June 15, 2023)

Meghan Vankosky
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Week 6

This year it is as important as ever to scout and to monitor insect populations at the field-scale.

Grasshoppers thrive in warm, dry conditions. Some 5th instar nymphs were spotted in ditches in southwestern Saskatchewan in the past week, although there are many first, second, third, and fourth instar nymphs active as well. Signs of damage in the roadsides and field edges are being reported.  

Diamondback moths develop rapidly when it is warm and their population densities can build up quickly with each generation. Be ready to scout if pheromone traps in your area have detected diamondback moths this spring and watch the provincial websites and PPMN updates for pheromone trap results.  

Bertha armyworm development is also well ahead of schedule. Watch the provincial websites in Alberta, Saskatchewan, and Manitoba for reports on bertha armyworm pheromone trap captures for your area over the next few weeks; these provide an estimate of regional risk and are meant to guide in-field scouting.

This week, the Insect of the Week featured the strawberry blossom weevil. This is an invasive insect to Canada that is currently found in BC, but it is important to watch for it on the prairies in raspberry and strawberry patches.

Please read this week’s posts in the Weekly Update for more information about the insects listed above and for a sneak peak of wheat midge development!

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

To receive Weekly Updates automatically, please subscribe to the website!

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 6

The week of June 5-11, 2023 was characterized by average prairie temperatures that continue to be well above average. The prairie average daily temperature was 3.5°C warmer than normal (Fig. 1). Like last week, the warmest temperatures were observed across Manitoba and eastern Saskatchewan. 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 5 – 11, 2023. 

Average temperatures over the past 30 days (May 13 to June 11, 2023) have been 4°C above normal with the warmest values being reported across Manitoba and Saskatchewan (Fig. 2). Average 30-day temperatures ranged from 14.2°C at High Level, Alberta to 20°C at Morden, Manitoba.  

Figure 2. 30-day average temperature (°C) across the Canadian prairies for the period of May 13 to June 11, 2023. 

Seven-day cumulative rainfall was nominal for most of Alberta and western Saskatchewan while significantly higher rainfall amounts were reported for eastern Saskatchewan and Manitoba (Fig. 3). Southern Alberta, including Lethbridge and Taber reported weekly rainfall totals that were greater than 25mm up to June 11. Winnipeg and Minnedosa, Manitoba reported more than 45mm.

Figure 3. Seven-day cumulative rainfall (mm) observed across the Canadian prairies for the period of June 5-11, 2023. 

Eastern Saskatchewan has generally had the highest rainfall totals over the past 30 days. Rainfall amounts continue to be low across Alberta and Manitoba (central and eastern regions) (Fig. 4). In Alberta, a large region that extends from Lethbridge to Edmonton, is extremely dry – this area has received only 40% of the precipitation normally expected for this time of year in the last 30 days. Central and eastern regions of Manitoba have also had less than 40% of normal precipitation. A large region extending north from an area that extends from Brandon, Manitoba to North Battleford, Saskatchewan has had above normal precipitation.  

Figure 4. 30-day cumulative rainfall (mm) observed across the Canadian prairies for the period of May 13 to June 11, 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). Central and southern regions of Alberta are categorized as relatively cool/dry. The Peace River region has been cool and wet. Eastern Saskatchewan and a number of western Manitoba locations are now categorized as warmer and wetter. 

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 13 to June 11, 2023. The red line indicates average temperature and the blue line represents average rainfall (for the period of May 13 to June 11, 2023). 
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Wind Trajectory Summary

Ross Weiss, Serge Trudel and Meghan Vankosky
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Week 6

‘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. 

There was a significant decrease in the number of reverse trajectories that entered the Canadian prairies during the week of June 7-13, 2023 as compared to the previous week (Fig. 1).   

Figure 1. The average number (based on a 5-day running average) of reverse trajectories (RT) that have crossed the prairies for the period of May 14 to June 13, 2023. 

Mexico, California and Texas: Only 5 reverse trajectories crossed into the prairies from Mexico, California, and Texas from June 7-13. These trajectories were expected to cross into southeastern Saskatchewan and Manitoba (Fig. 2).

Figure 2. Total number of dates with reverse trajectories originating over Mexico, California and Texas that have crossed the prairies between April 1 and June 13, 2023. 

Pacific Northwest (Idaho, Oregon, Washington): This week 40 reverse trajectories were predicted to cross the prairies from the Pacific Northwest. The majority of the reverse trajectories from the Pacific Northwest passed over Alberta and western Saskatchewan (Fig. 3).   

Figure 3. Total number of dates with reverse trajectories originating over the Idaho, Oregon, and Washington that have crossed the prairies between April 1 and June 13, 2023. 

Oklahoma and Texas: There were 17 reverse trajectories that originated over Texas and Oklahoma and passed through the prairies in the past week. These reverse trajectories largely passed over Manitoba and southeastern Saskatchewan and (Fig. 4).  

Figure 4. The total number of dates with reverse trajectories originating over Oklahoma and Texas that have crossed the prairies between May 1 and June 13, 2023. 

Kansas and Nebraska: Since April 1, reverse trajectories originating in Kansas and Nebraska were reported to cross southeastern Saskatchewan and southern Manitoba (Fig. 5). This week (June 7-13), there were 46 reverse trajectories, originating over Kansas and Nebraska that were predicted to pass over Saskatchewan and Manitoba. 

Figure 5. The total number of dates with reverse trajectories originating over Kansas and Nebraska that have crossed the prairies between May 1 and June 13, 2023. 
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Predicted Grasshopper Development

Ross Weiss, Tamara Rounce, Owen Olfert, Jennifer Otani and Meghan Vankosky
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Week 6

Model simulations were used to estimate development of grasshoppers as of June 11, 2023. Well above normal temperatures across the prairies continue to result in rapid grasshopper development. Model runs suggest that this spring’s hatch is almost complete. As of June 11, grasshopper nymphs should range from the first to fourth instar in many locations on the prairies. Based on average instar, development is most advanced across the southern prairies where populations should consist of mainly third and fourth instar nymphs (Fig. 1). 

Figure 1. Predicted grasshopper (Melanoplus sanguinipes) development, presented as average instar, across the Canadian prairies as of June 11, 2023. 

At some locations between in central Saskatchewan (between Saskatoon and Swift Current), some fifth instar grasshopper nymphs have been captured in sweep net samples and the number of nymphs in the fourth instar has increased. Two-striped grasshoppers continue to be most prevalent in this region, but more first instar nymphs of the other primary pest species were observed in ditches in Saskatchewan this week. From the roadsides, there were some signs of grasshopper damage to crop plants, including canola, along field edges.

Models and geospatial maps are tools to help time in-field scouting on a regional scale but grasshopper development can vary and is only accurately assessed through scouting. Producers are advised to monitor roadsides and field margins to assess the development and densities of local grasshopper populations. Due to the small size, it may be difficult to visually observe first and second instar grasshoppers in roadside vegetation and field margins. If possible, grasshopper assessments should be conducted with sweep nets. This will permit assessment of grasshopper densities, stage and species present.  

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 6

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. Typically, there are three to four non-migrant generations of diamondback moths on the prairies.

Diamondback moth development can be rapid during periods of warm weather. Model simulations to June 11, 2023, indicate that the second generation of non-migrant adults (based on early-May arrival dates) is currently occurring across the southern 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 June 11, 2023. 

On the prairies, we use a network of pheromone traps to detect the first spring appearance of diamondback moths. In the June 7 and June 14 issues of the Manitoba Crop Pest Update, some diamondback moth trap locations in the central and eastern parts of the province reported catching between 100-200 adult moths. At least three sites in central and southern Alberta (use the link to see the live map) have also caught between 100-200 moths so far this year. Lower numbers have been recorded so far in Saskatchewan in 2023.

Now, 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.

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Predicted Bertha Armyworm Development

Ross Weiss, Tamara Rounce, Owen Olfert, Jennifer Otani and Meghan Vankosky
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Week 6

Based on model simulations, development of overwintered bertha armyworm (Mamestra configurata) continues to be 7-10 days ahead of normal. Where present, we expect the majority of the prairie population of bertha armyworm to now be in the adult stage (Fig. 1) and females have likely already begun to lay eggs (Fig. 2).

Figure 1. Proportion (%) of the bertha armyworm (Mamestra configurata) population that is expected to be in the adult stage across the Canadian prairies as of June 11, 2023. 

Figure 2. Proportion (%) of the bertha armyworm (Mamestra configurata) population that is expected to be in the egg stage across the Canadian prairies as of June 11, 2023. 

Bertha armyworm populations were very low in 2022. So far, trap catches in Alberta in 2023 have also been very low (most traps with less than 20 adult male moths). A few trap locations in Saskatchewan and at least one in Manitoba have reported more than 100 moths caught since the traps were set up in late May or early June.

Pheromone trap monitoring for bertha armyworm provides a regional picture of potential risk. Cumulative trap catches below 300 generally represent low risk. To know if a specific field is at risk of economic yield losses, scouting for larvae in that field is required. The PPMN protocol for bertha armyworm monitoring provides information about scouting for adult and larval bertha armyworm and about economic thresholds for this pest.

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Predicted Wheat Midge Development

Ross Weiss, Tamara Rounce, Owen Olfert, Jennifer Otani and Meghan Vankosky
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Week 6

Wheat midge (Sitodiplosis mosellana) overwinter as larval cocoons in the soil. Adequate rainfall in May and June is a signal to larval cocoons to end their diapause and move to the soil surface to pupate. 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. The Olfert et al. (2020) model indicated that dry conditions may result in delayed adult emergence, delayed oviposition by female wheat midge, fewer adults, and fewer eggs laid.

In the last few weeks, rainfall events over parts of the prairies may have provided the cue to end wheat midge larval diapause. Cumulative rainfall from May 1 to June 11 across western Manitoba, most of Saskatchewan and northwestern Alberta now exceeds the threshold of 30 mm of rain required to terminate the larval diapause of wheat midge (Fig. 1).

Figure 1. Areas in western Canada where cumulative rainfall from May 1 to June 11, 2023 is equal to or greater than 30 mm, which is the threshold required to promote movement of wheat midge (Sitodiplosis mosellana) larvae to the soil surface where they will pupate.  

The wheat midge model indicates that, where wheat midge populations are present, larvae have begun to move to the soil surface in some areas of the prairies (Fig. 2). 

Figure 2. Percent of the wheat midge larval population (Sitodiplosis mosellana) that has moved to the soil surface across western Canada, as of June 11, 2023. 

In contrast to the wet areas on the prairies, wheat midge adult emergence might be delayed in 2023 in areas that have not yet received much rain. It is also possible that the wheat midge larval cocoons will remain in a diapause state in the dry areas of the prairies until a future year when spring moisture is more suitable for wheat midge development.

Scouting for adult wheat midge usually starts in late June or early July. Over the next few weeks, the Prairie Pest Monitoring Network will continue to use phenology models to predict that status of wheat midge development and 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

Shelley Barkley, James Tansey, John Gavloski and Meghan Vankosky
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Week 6

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.

Watch for new issues of the Saskatchewan Crop Production News coming soon in 2023 and browse the articles from 2022 for information from the past.

The latest Manitoba Crop Pest Update for 2023 was posted on June 14. Watch their website for new Crop Pest Updates as the season continues and check out the archives to read past Updates.

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INVASIVE PEST ALERT: STRAWBERRY BLOSSOM WEEVIL

Michelle Franklin and Meghan Vankosky
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Week 6

Strawberry blossom weevil (Anthonomus rubi), a recent invader of the Fraser Valley of British Columbia (BC), has been busy clipping buds this spring in strawberry and raspberry fields. This weevil was first spotted in raspberries in Abbotsford, BC in 2019. Native to Europe, Asia, and parts of North Africa, this weevil is now established in the Fraser Valley of BC and northwestern Washington state. It has not yet been found in the prairie provinces.

Damage to strawberry buds from the strawberry blossom weevil. Photo credit: Michelle Franklin, AAFC-Agassiz.

Different from many of the nocturnal root feeding weevils that damage roots and stunt plant growth in berries, strawberry blossom weevil is active during the day. It is small (2-3 mm long) with a small white patch of scales on the scutellum (back) and a long slender rostrum (snout). The female weevil is the main source of damage, as she deposits her eggs inside of green developing buds. She first chews a hole in the bud and then turns around and lays an egg inside, after which she clips the stem below.

A female strawberry blossom weevil laying an egg into a Himalayan blackberry bud. Photo credit: Warren Wong.

Typically a single c-shaped larvae develops inside of a bud. The larvae then pupates and the adult weevil emerges from the bud by chewing an exit hole.

A strawberry blossom weevil larva, about 2.5 mm long, inside a berry bud. Photo credit: Warren Wong.

We are currently investigating the impact of this new weevil on strawberry and raspberry crops in the Fraser Valley of BC. Reports from its native range in Europe indicate that bud losses associated with strawberry blossom weevil range widely from 5 to 90% and yield losses over 60% have been reported. Despite the name, strawberry blossom weevil uses a wide range of host plants in the family Rosaceae – including the invasive Himalayan blackberry and ornamental plants such as rose and potentilla. The United States Department of Agriculture Animal and Plant Health Inspection Service (APHIS) put a Federal Order in place in September 2021 and continues to require a phytosanitary certificate to move Fragaria, Rubus, and Rosa plants from Canada into the USA (Federal Order DA-2021-25).

We need your help surveying for this pest!  Although strawberry blossom weevil has not been detected beyond the Fraser Valley of BC, we are continuing a nation-wide survey in summer 2023 for this pest. Adult weevils naturally drop when disturbed so they can be detected by a method called beat sampling – where plants are tapped from above and weevils are collected into a tray below. Like many other insects, they are also attracted to the colour yellow and can be collected on yellow sticky cards. Visual surveys for damaged buds with severed stems can also be useful when searching for strawberry blossom weevil.  In collaboration with Agriculture and Agri-Food Canada’s Geomatics Team we have developed a Story Map for Strawberry Blossom Weevil to summarize our survey efforts thus far.

If you see a weevil you suspect to be strawberry blossom weevil, snap a picture and submit it to our iNaturalist project (Anthonomus rubi in North America · iNaturalist).

For more information, check out factsheets prepared by the Invasive Species Council of BC, the CFIA, and the province of BC.

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