2023 Week 15 (Released August 17, 2023)

Meghan Vankosky
Week 15

Insect scouting season continues, even though harvest has already started in some regions! Development of many pest insects has been ahead of schedule all year in most parts of the prairies, thanks to warmer than average weather during this growing season.

Adult grasshoppers are now in flight and will be laying eggs across the prairie region. Scouting individual fields is the best way to estimate crop risk. At this time of year, we start to look forward to next season. Insect surveyors are working to estimate grasshopper populations in ditches/roadsides and may be collecting samples of adult grasshoppers for species identification.

Aside from grasshoppers, fall surveys for wheat midge and wheat stem sawfly will begin as harvest is completed in Alberta and Saskatchewan. This week, the Insect of the Week post features wheat stem sawfly, including information about how to estimate their population densities in the fall.

Diamondback moth, if present, are into the fourth non-migrant generation across most of the prairies now and could be starting a fifth generation in some southern parts of the prairies. Keep in mind that diamondback moth develop quickly in warm weather which could lead to rapidly increasing populations over the summer.

On the topic of diamondback moths, Dr. Maya Evenden’s lab at the University of Alberta is conducting research on diamondback moth, flea beetles, and alfalfa weevil. Learn more about Maya’s research program in this week’s Prairie Research post.

Use the links in the Provincial Insect Updates post to learn more about what is happening with populations of insect pests (and beneficial insects) in your province.


1) There are many resources available to help with planning for late-season insecticide applications to ensure Pre-Harvest Interval requirements are met.

2) Insect Monitoring Protocols containing information about in-field scouting as well as information about insect pest biology and identification are available from the Prairie Pest Monitoring Network.

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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.


Weather Synopsis

Ross Weiss, Tamara Rounce, Jennifer Otani and Meghan Vankosky
Week 15

The Parkland region of Alberta, Manitoba, and Saskatchewan experienced cooler temperatures and rain in the past week, but warm, dry conditions continue to persist across most of the southern prairies. This past week (August 7-13, 2023), the prairie average daily temperature was slightly cooler than the long-term average. The coolest temperatures occurred across the central and eastern areas of the Parkland region (Fig 1). In comparison to the Parkland region, temperatures were much warmer across southern Alberta and southwest Saskatchewan.

Figure 1. Seven-day average temperature (°C) observed across the Canadian prairies for the period of August 7 to 13, 2023. 

Precipitation for the period of August 7-13, 2023 was highest for a large region northeast of Edmonton in Alberta, east of Saskatoon and north of Regina in Saskatchewan, and in most of Manitoba (Fig. 2). Southern Alberta has been extremely dry all of summer 2023 and that trend continued in the last week (Fig. 2). Similarly, it has continued to be dry in southwestern Saskatchewan.

Figure 2. Seven-day cumulative rainfall (mm) observed across the Canadian prairies for the period of August 7-13, 2023. 

This year, we used scatterplots for growing season average temperature and total rainfall to provide relative comparisons of site specific growing conditions across the prairies. Growing season temperature and precipitation has varied significantly across the prairies in 2023. Lethbridge has had less than 100 mm of rain, for example, while Grande Prairie has reported 250 mm. Growing season average temperatures have ranged from 12.3°C to 15.4°C. Northwestern Alberta locations are categorized as relatively cool and wet in 2023 (Fig. 5). In contrast, most locations in the southern prairies can be characterized as warm and dry.  

Figure 3. Site-specific comparison of growing season average temperature (°C) and cumulative rainfall (mm) observed across the Canadian prairies for the period of April 1 – August 13, 2023. The red line indicates the average temperature and the blue line represents the average rainfall. 

Predicted Diamondback Moth Development

Ross Weiss, Tamara Rounce, Owen Olfert, Jennifer Otani and Meghan Vankosky
Week 15

After arriving in western Canada in the spring, migrant diamondback moths begin to reproduce. In western Canada, there are usually up to four non-migrant generations of diamondback moth produced in ‘local populations’ during the growing season.

Due to warm weather in 2023, development of diamondback moth populations is well ahead of average development. Model simulations to August 13, 2023, indicate that the fourth generation of non-migrant adults (based on early May arrival dates) are currently occurring across the Canadian prairies (Fig. 1) and that fifth generation non-migrant adults could also be occurring in some localized areas of the southern prairies.

Figure 1.  Predicted number of non-migrant generations of diamondback moth (Plutella xylostella) expected to have occurred across the Canadian prairies as of August 13, 2023.  

In a ‘normal year’ based on climate normals data (e.g., 30-year averages), we would expect only the third generation of non-migrant diamondback moth to be occurring across the northern prairie region at this time of year, with the fourth generation occurring across the extreme southern region of the prairies (Fig. 2).

Figure 2. The predicted number of non-migrant generations of diamondback moth (Plutella xylostella) expected to have occurred across the Canadian prairies as of August 13, based on climate normals data.

Considering advanced canola development, risk across the southern and central regions of the prairies associated with the development of a fifth generation of diamondback moth should be minimal. However, in regions where broccoli, rutabaga, and other brassica vegetables are grown and where crops are late to mature, these crops could still be at risk. Keep scouting for diamondback moth where crops are still green and could provide a desirable food source for developing diamondback moth larvae.

To scout for diamondback moth, estimate the number of diamondback moth larvae per m2 at several locations in a field. The economic threshold for diamondback moth is NOT based on pheromone traps or sweep net samples, but on the density of larvae per plant. For immature and flowering canola, the economic threshold is 100-150 larvae/m2. In podded canola, the economic threshold is 200-300 larvae/m2. See the Field Crop and Forage Pests guide and monitoring protocol for more information about scouting for diamondback moth.


Prairie Research: The Evenden Lab

Maya Evenden and Meghan Vankosky
Week 15

*Text for this post prepared by Priyatha Sundaran, Sharavari Kulkarni and Maya Evenden, from the University of Alberta.

Dr. Maya Evenden’s lab in the Department of Biological Sciences at the University of Alberta researches insect behaviour, chemical ecology and integrated pest management. They study how insects orient and maneuver in their environment and exploit that knowledge for the development of IPM tactics. This summer the Evenden lab has multiple agriculture-based projects targeting diamondback moth, flea beetles, pea leaf weevil and alfalfa weevil. Here we highlight the work of an MSc student, Priyatha Sundaran, and a postdoctoral fellow, Dr. Sharavari Kulkarni.

Priyatha’s research focuses on the presence and distribution of alfalfa weevil (Hypera postica), in alfalfa grown for seed in southern Alberta. The study also assesses the diversity of Sitona spp. in sampled alfalfa fields. In three field seasons, alfalfa weevils have been sampled with soil and sweep samples, and emergence and pit fall traps. Soil samples at the beginning and end of each crop season estimate the density of alfalfa weevils in the soil over the winter. Sweep net samples can collect both larvae and adults to monitor alfalfa weevil density in the field for timely use of insecticides. Pitfall trap capture can indicate weevil movement in and out of the field over the course of the growing season. Emergence cages assessed the overwintering locations of weevils inside and outside the field. Initial results reinforce the effectiveness of sweep net sampling to monitor alfalfa weevil populations with peak larval activity in June-July. Alfalfa weevils were captured in equal numbers in pitfall traps placed at the edge and in the interior of the field suggesting that alfalfa weevils remain within alfalfa fields, unlike in other parts of their range. Sitona spp. bycatch consisted mostly of alfalfa curculio (Sitona lineellus) and pea leaf weevil (Sitona lineatus).

Alfalfa weevil sampling methods used in alfalfa fields grown for seed: A) Emergence cages were located inside and outside the field to reveal the overwintering sites of alfalfa weevils. B) Two hundred sweep samples were collected from four locations in each field throughout the growing season in three seasons. C) Directional pitfall traps were employed in the 2023 season to measure the direction of movement of alfalfa weevils in the field. Pictures by Priyatha Sundaran, University of Alberta.

Sharavari’s research focuses on developing weather-based stage-structured predictive models for two important canola pests, striped flea beetles, (Phyllotreta striolata (Fab.)) and crucifer flea beetles (Phyllotreta cruciferae (Goeze)). Flea beetles are oligophagous species feeding mainly on canola (Brassica napus L. and Brassica rapa L.) and mustard (Brassica juncea L.). Sharavari used field surveys to assess local phenology and laboratory bioassays to study the effect of temperature on beetle development and interspecific competition between the two species. The flea beetle surveys were conducted in the spring (pre-seeding) and fall of 2021, 2022 and 2023 across 20+ canola fields throughout Alberta.  Season-long, site-specific weather data was collected for modeling and validation. None of the available monitoring methods provides accurate forecasting for flea beetles, and weather-based phenology models can help producers make informed decisions on timing and the need to apply foliar insecticides for flea beetle management.  Lab assays showed a dramatic effect of temperature on the time and success of egg hatch and development time from egg to adult.  On-going lab work is testing for plant-mediated interactions between the two species to understand if P. cruciferae prefers to feed and oviposit on plants previously damaged by P. striolata and to determine if inter-species interactions have fitness costs.

Flea beetle monitoring in commercial canola fields with yellow sticky cards at sites with weather stations for site-specific temperature measurements. Pictures by Sharavari Kulkarni, University of Alberta.

Provincial Insect Updates

Shelley Barkley, James Tansey, Meghan Vankosky and John Gavloski
Week 15

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 cabbage seedpod weevil.

Saskatchewan Crop Production News issues are now online! Issue 4 is available now, as well as a Crop Report covering the period of August 1 to August 7. The crop report notes that grasshoppers and flea beetles are causing some late season damage to crops. There are links on the Crop Production News page so that interested readers can subscribe to the newsletter or read issues from past years.

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). The August 16 issue provides an update on Lygus bugs, diamondback moth, flea beetles, grasshoppers and aphids. It also has great pictures to help identify insect pests!


Pre-Harvest Intervals (PHI)

Meghan Vankosky and Jennifer Otani
Week 15

As harvest gets started, it is necessary to consider PHI before applying pesticides for late-season pests. The PHI refers to the minimum number of days between a pesticide application and swathing or straight combining of a crop and reflects the time required for pesticides to break down after being applied. PHI values are both crop- and pesticide-specific.  Adhering to the PHI is important for a number of health-related reasons and to ensure that crops being sold for export meet pesticide residue limit requirements.

Helpful resources include:
• The Keep It Clean website, with information about PHI and Maximum Residue Limits (MRL)
• The Pest Management Regulatory Agency fact sheet, “Understanding Preharvest Intervals for Pesticides”, with a free copy available to download
• Keep It Clean’s “Pre-Harvest Interval Calculator” that will help to accurately estimate PHI for a variety of crops
• The Pre-Harvest Glyphosate Stage Guide
• The provincial crop protection guides include the PHI for every pesticide by crop combination. The 2023 Crop Protection Guides are available as FREE downloadable PDFs for AlbertaSaskatchewan, and Manitoba.


Wheat Stem Sawfly

Amanda Jorgensen, Shelby Dufton, Jennifer Otani and Meghan Vankosky
Week 15

Native to North America, the wheat stem sawfly is an economic pest depending on spring and durum wheat as its main crop hosts. These insects also target winter wheat, rye, grain corn and barley, in addition to feeding on native grass species. It is interesting to note that wheat stem sawflies do not feed on oat crops, as oats are toxic to wheat stem sawfly.

An adult wheat stem sawfly. Picture by Dylan Sjolie, AAFC-Saskatoon.

Wheat stem sawfly larvae feed on pith inside the stems of their host plant. Their feeding activity affects crop yield and quality. As infested host plants mature, the larvae travel down the stem to its base, where “V” shaped notches are cut into the stem a little above ground level. These notches leave plants vulnerable to collapsing or lodging, especially during wind events. Because wheat stem sawflies also breed and develop on native grass species, economic damage tends to be most prevalent around crop margins where native and agricultural plants are found close together.  

An adult wheat stem sawfly. Picture by Dylan Sjolie, AAFC-Saskatoon.

Adult wheat stem sawflies are 8–13 mm long with a wasp-like resemblance, due to their black body and yellow legs. Females have an egg-laying organ (an ovipositor) that extends from their abdomen. When resting on plant stems, these insects will point their heads downward. Mature larvae are 13 mm long and resemble whitish worms with brown heads. 

Biological and monitoring information related to wheat stem sawflies in field crops can be found on our Monitoring Protocols page as well as on provincial Agriculture Ministry pages (Manitoba, Saskatchewan and Alberta). For more information, visit the wheat steam sawfly page in 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).