2023 Week 2 (Released May 17, 2023)

This is Week 2 of the 2023 Prairie Pest Monitoring Network Weekly Updates!

Spring weather continues to be hot and dry across the prairies, bringing some challenging conditions for #Plant2023. Please stay safe.

Grasshoppers thrive in warm, dry conditions and there are reports that first instar nymphs are already hatching. Diamondback moths are appearing in pheromone traps across the prairies, albeit in low numbers so far. For more information, check out the posts in the Weekly Update! The Insect of the Week is about cutworms this week – read on and check out the links for more information.

The prairie-wide maps summarizing the results from the 2022 growing season are online and available for review, as are the historical insect pest distribution maps. These prairie-wide geospatial maps offer insight into potential risk and help growers prioritize their scouting lists.

Remember, insect Monitoring Protocols containing helpful insect pest biology, how and when to target in-field scouting, and even thresholds to help support in-field management decisions are all available for review or download.

To receive free 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.

Weather Synopsis

Similar to the previous week, this past week (May 8-14, 2023) was warmer and drier than normal. The average temperature across the prairies was 5°C warmer than normal (Fig. 1). This week, the warmest temperatures were observed across southern Manitoba, the northern Peace River region, and across a region that extended between Saskatoon and Edmonton. The coolest weekly temperatures were observed over southern regions of Alberta and Saskatchewan.

Figure 1. Seven-day average temperature (°C) observed across the Canadian prairies for the period of May 8-14, 2023.

Since April 1, the 2023 growing season has been marginally cooler than average across eastern Saskatchewan and Manitoba (Fig. 2). Alberta temperatures continue to be above average. Relative to climate normals, growing season temperatures have been well above normal in the Peace River region. Fort Vermillion has been 4.7°C warmer than normal and Manning has been 3°C warmer than normal.

Figure 2. Growing season average temperature (°C) observed across the Canadian prairies for the period of April 1 to May 14, 2023.

Seven-day cumulative rainfall was greatest across the southern prairies and central regions of Alberta (Fig. 3). Central regions of Saskatchewan received minimal rain over the past seven days. Growing season rainfall (April 1 to May 14) has been below normal across most of the prairies (Fig. 4). A large region, extending from Lethbridge to Saskatoon to the Peace River region has received well below normal rainfall accumulations so far in 2023.

Figure 3. Seven-day cumulative rainfall (mm) observed across the Canadian prairies for the period of May 8-14, 2023.

Figure 4. Growing season cumulative rainfall (mm) observed across the Canadian prairies for the period of April 1 to May 14, 2023.

Using Trajectories to Monitor Insect Movement

Agriculture and Agri-Food Canada (AAFC; Ross Weiss, Meghan Vankosky) and Environment and Climate Change Canada (ECCC; Serge Trudel) have been working together to study the potential of trajectories for monitoring insect movements since the late 1990s. Trajectory models are used to deliver an early-warning system for the origin and destination of migratory invasive species, such as diamondback moth.  In addition, plant pathologists have shown that trajectories can assist with the prediction of plant disease infestations and are also beginning to utilize these same data. We receive two types of model output from ECCC: reverse trajectories and forward trajectories. 

‘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.

Wind Trajectory Summary to May 16, 2023

Since May 1, 2023, the majority of the reverse trajectories that have crossed the prairies originated from the Pacific Northwest (Idaho, Oregon and Washington) (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 1-16, 2023.

Mexico, California and Texas – Very few reverse trajectories that originated from Mexico, California or Texas have passed over the Canadian prairies so far in May 2023.

Pacific Northwest (Idaho, Oregon, Washington) – The majority of Pacific Northwest reverse trajectories have been reported to pass over south-central Alberta and southwestern Saskatchewan (Fig. 2).  

Figure 2. Total number of dates with reverse trajectories originating over the Idaho, Oregon, and Washington that have crossed the prairies between April 1 and May 16, 2023.

Oklahoma and Texas – Since April 1, reverse trajectories from Oklahoma and Texas were reported to cross the southern prairies (Fig. 3).

Figure 3.  The total number of dates with reverse trajectories originating over Texas and Oklahoma that have crossed the prairies between May 1 and May 16, 2023.

Kansas and Nebraska – Since April 1, reverse trajectories were reported to cross southeastern Saskatchewan and southern Manitoba (Fig. 4).

Figure 4.  The total number of dates with reverse trajectories originating over Kansas and Nebraska that have crossed the prairies between May 1 and May 16, 2023.

Predicted Grasshopper Development

Model simulations were used to estimate development of grasshopper eggs as of May 14, 2023. Compared with average spring temperatures, temperatures in Alberta and western Saskatchewan have been well above average so far in 2023. Unseasonably warm temperatures continue to contribute to rapid grasshopper egg development (Fig. 1). Compared to egg development expected if temperatures were like long-term to climate normals (Fig. 2), egg development in 2023 is well ahead of average (Fig. 1). Cool conditions in Manitoba have resulted in slower development rates that are similar to long-term average development rates.

Figure 1. Predicted grasshopper (Melanoplus sanguinipes) embryological development across the Canadian prairies as of May 14, 2023. 

Figure 2. Long-term average predicted grasshopper (Melanoplus sanguinipes) embryological development across the Canadian prairies as of May 14, based on climate normals data. 

As a result of above normal temperatures, model outputs predict that grasshopper eggs have already started to hatch across Alberta and western Saskatchewan (Fig. 3). We have received reports of grasshopper nymphs from both provinces. This spring, grasshopper eggs are hatching approximately 10 days earlier than normal. Areas with highest densities of adult grasshoppers in summer of 2022 overlap with regions with greatest predicted egg development so far in spring of 2023 (Fig. 4), including a large region extending from south of the Yellowhead Highway corridor to the Canada-USA border. Prairie farmers should be scouting for grasshoppers early this spring and summer, especially if conditions remain warmer and drier than normal over the next few weeks.

Figure 3. Predicted grasshopper (Melanoplus sanguinipes) hatch (%) across the Canadian prairies as of May 14, 2023.

Figure 4. Estimated grasshopper population densities in late summer and early fall 2022 in western Canada; areas with high grasshopper densities in 2022 are at risk of high grasshopper densities and associated damage in 2023, based on knowledge of the life history of the primary pest species, including Melanoplus sanguinipes (migratory grasshopper) (map by Ross Weiss, AAFC-Saskatoon).

Test your grasshopper knowledge by taking the Canola Watch quiz!

Predicted Diamondback Moth Development

It has been suggested the overwintering mortality of diamondback moth (DBM) is high on the prairies. DBM, carried on upper air currents, may be introduced to the prairies from overwintering sites in southern USA and the US Pacific Northwest. Analysis of wind trajectory data (from Environment and Climate Change Canada) indicated that a number of upper air currents, originating over the US Pacific Northwest, passed over the Peace River region during the last week of April and first two weeks of May. DBM development can be rapid during periods of warm weather. Shelley Barkley (Alberta Agriculture and Irrigation) reports that DBM adults have been collected from a number of traps across Alberta. In Alberta, trap captures of DBM have been highest near Grande Prairie. Similarly, Carter Peru and James Tansey (Saskatchewan Ministry of Agriculture) note that adult DBM have been collected on traps located across Saskatchewan.

During the growing season, results from the DBM monitoring program in Saskatchewan will be    available here (scroll to the bottom of the page) and results from Alberta will be available here.

The life stages of diamondback moth, Plutella xylostella: (A) eggs, (B) early instar larva, (C) late instar larvae, (D) pupa, and (E) adult moth. Photo credit: Jonathon Williams, AAFC-Saskatoon (all pictures)

DBM were collected during the first and second weeks of May. Thus, the DBM model was initialized for May 1, 2023 and run to May 14. Though canola may not be present, results indicate that females may have started to lay eggs on brassicaceous plants (e.g., volunteer canola, flix weed) and larvae may have hatched from early-laid eggs. In the Grande Prairie area, for example, both eggs and first instar larvae may already be present (Fig. 1).

Figure 1. Predicted development of diamondback moth (Plutella xylostella) near Grande Prairie, AB as of May 14, 2023.


Growers are out seeding, and the cutworms are ready for it – the time to start scouting for cutworms is now! Scouting occurs by manually examining plant foliage and digging in the soil near damaged or missing plants – focus on transition zones between damaged and healthy plants. Even if you have not started seeding a field yet, consider checking volunteer plants for cutworms or feeding damage. General cutworm monitoring protocols can be found on the Monitoring Protocols page. Species-specific protocols can be found in the Cutworm Pests of Crops on the Canadian Prairies

There are over 20 cutworm species that can cause economic damage to your crop, each with different feeding behaviour, preferred hosts, and lifecycle. Cutworms will feed on prairie-grown commodities including canola, mustard, wheat, barley, triticale, peas, alfalfa, clover, fescue, and timothy. Species identification is especially important! It helps growers determine how and when to scout, whether the cutworm species is found above-ground (climbing) or below-ground, recognize damage, and choose appropriate control options. The species of cutworm will also determine the time of day for monitoring and applying controls. 

Action and economic thresholds exist for many of the cutworm species – please use them. Thresholds help control costs by eliminating unnecessary and non-economic spraying and reduce your impact on non-target insects. These non-target insects include the natural enemies that work in the background to control cutworm populations! 

Pale western cutworm, Phil Sloderbeck, Kansas State University, Bugwood.org (cc-by-nc 3.0)

This week’s Insect of the Week is the Pale Western Cutworm. This cutworm feeds below ground, with larvae hatching in late April through early May. Young larvae tunnel through the soil, producing holes on newly emerged shoots and furled leaves. Older larvae will sever plants just below the soil surface and may pull and eat the severed shoots underground. Mature larvae are a pale greenish gray, with a yellow, black striped head.