May was characterized by wonky weather – unseasonably warm days and very little rain. As a result, some prairie insect pests are developing faster than normal.
Grasshoppers thrive in warm, dry conditions and we continue to hear about high numbers of nymphs along roadsides and field edges. Last week, we also observed some third instar grasshopper nymphs, which normally do not appear in the population until mid-June. Diamondback moths that arrived in early May have likely reproduced and adult moths found now could be from the first generation produced on the prairies. Bertha armyworm development is also well ahead of schedule – pupal development could be 90% complete in some areas, so it is probably time to set up pheromone traps for bertha armyworm monitoring in most parts of the prairies. This week, we featured the pea leaf weevil in the Insect of the Week – the annual damage survey for pea leaf weevil is now underway! For more information, check out the posts in the Weekly Update!
Remember, insect Monitoring Protocols containing helpful insect pest biology, how and when to plan for in-field scouting, and even thresholds to help support in-field management decisions are all available for review or download.
Questions or problems accessing the contents of this Weekly Update? Please contact Dr. Meghan Vankosky (firstname.lastname@example.org) to get connected to our information. Past Weekly Updates, full of information and helpful links, can be accessed on our Weekly Update page.
***Special thanks to Mark Berry, AAFC-Geomatics, for providing up-to-date weather information for the prairies that is summarized here and used to predict insect development***
This past week (May 22-28, 2023), average prairie temperatures continued to be well above average. The prairie average daily temperature was 4°C warmer than normal (Fig. 1). The warmest temperatures were observed across southern regions of Manitoba and Saskatchewan. Even though temperatures have moderated across the Peace River region, temperatures were still 2-3°C warmer than normal for this time of year.
Average temperatures over the past 30 days (April 28 – May 28, 2023) have been 4°C above normal (Fig. 2), with the warmest temperatures reported for Alberta and western Saskatchewan.
Since April 1, the 2023 growing season has been coolest across eastern Saskatchewan and western Manitoba (Fig. 3). Temperatures have been below normal for many locations across western Manitoba. For example, the average temperature near Melita has been 1.3°C cooler than average. Alberta temperatures continue to be above average. Relative to climate normals temperatures, the warmest and most above average conditions continue to be those in the Peace River region. For example, the growing season temperature has been 5°C warmer than normal at Fort Vermillion, AB.
Seven-day cumulative rainfall was nominal for most of Alberta and Manitoba last week (Fig. 4). Central Alberta and southern locations in the Peace River region received much need rain. Grande Prairie, Alberta reported 65 mm and Peace River, Alberta reported 59 mm. Saskatoon, Saskatchewan reported 41 mm.
Rainfall over the past 30 days has been highly variable across the prairies (Fig. 5). Recent rainfall in the Peace River region has resulted in many locations in that region having rainfall amounts that are 200% of normal. Conversely eastern Alberta and western Saskatchewan have had rainfall amounts that are well below normal. Over the past 30 days rainfall totals are less than 60% of normal across most of Alberta, northwestern and eastern Saskatchewan and Manitoba.
Growing season rainfall has been greatest across southern Saskatchewan and southern areas of the Peace River region; rainfall amounts have been low for most of the southern and central regions of Alberta, western Saskatchewan, and most of Manitoba (Fig. 6). A large region, extending from Lethbridge, Alberta to Edmonton, Alberta and into western Saskatchewan (to about Saskatoon) continues to have well below normal rainfall accumulations. At Hanna, Alberta for example, the total rainfall this growing season is only 40% of what would normally have accumulated by this time of year.
‘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 moth 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.
More reverse trajectories entered the Canadian prairies between May 25-31 than in the last two weeks (Fig. 1). With more reverse trajectories occurring, we may also see an increase in the introduction or migration of diamondback moths and aster leafhoppers to the prairies.
Mexico, California and Texas: Last week no reverse trajectories that entered the prairies that originated from Mexico, California or Texas. In comparison, 37 reverse trajectories from Mexico, California, or Texas crossed into the prairies this week (May 25-31). These trajectories were predicted to cross into southeastern Saskatchewan and Manitoba (Fig. 2)
Pacific Northwest (Idaho, Oregon, Washington): This week 55 reverse trajectories from the Pacific Northwest were predicted to cross the prairies, which is less than observed last week (n=79). The majority of Pacific Northwest reverse trajectories have been reported to pass over Alberta and western Saskatchewan (Fig. 3).
Oklahoma and Texas: This past week there were 38 reverse trajectories that originated over Texas and Oklahoma and passed through the prairies, particularly southeastern Saskatchewan and Manitoba (Fig. 4).
Kansas and Nebraska: Since April 1, reverse trajectories originating in Kansas and Nebraska were reported to cross southeastern Saskatchewan and southern Manitoba (Fig. 5). Between May 25 and May 31, 2023 there were 95 reverse trajectories that were predicted to occur. This is a significant increase over the previous week (n=9).
Over the past 5-7 days we have conducted a roadside survey for grasshoppers in west-central Saskatchewan. Numbers and development were higher than normal. First and second instar nymphs were found at all locations and many sites had low numbers of third instar grasshopper nymphs. We generally do not see third instars until mid-June! Many locations had high numbers of first instars suggesting that the hatch is still progressing. Melanoplus bivittatus, the two-striped grasshopper, was the most common species at all locations sampled in Saskatchewan in the last five days.
Our observations in the field over the last week agree with the model simulation used to estimate the status of grasshopper development as of May 28, 2023. Grasshopper development is progressing rapidly where temperatures have been well above normal in Alberta and western Saskatchewan. Model runs for 2023 suggest that egg development is 87% complete, on average. At the end of May in an average year, we would expect egg development to be only 72% complete. Recent warm conditions across southern Manitoba have also resulted in faster development rates for eggs.
Grasshopper eggs are now hatching across Alberta and in western and central regions of Saskatchewan (Fig. 1). Hatch rates are well ahead of expected hatch rates based on long-term average weather conditions. In central and eastern regions and across most of Manitoba, hatch is predicted to be less than 15% but hatch rate is increasing (15-45%) in southern Manitoba after some warmer weather last week.
2023 is shaping up to be an interesting year for grasshoppers and prairie farmers should be prepared to scout for grasshoppers, especially if conditions remain warmer and drier than normal. For more information about grasshopper scouting, biology, and management in your province (Alberta, Saskatchewan, Manitoba), please check out their resources available online.
Diamondback moths (Plutella xylostella) are a migratory invasive species to western Canada. 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, resulting in subsequent non-migrant populations that may have three or four generations during the growing season. DBM development can be rapid during periods of warm weather. Model simulations, initiated in early May and extendingto May 28, 2023, indicate that the first generation of non-migrant adults are currently occurring across the Canadian prairies (Fig. 1).
In-Field 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 dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
Based on model simulations, development of overwintered bertha armyworm (Mamestra configurata) pupae is rapidly progressing this spring (Fig. 1).
In fact, development is significantly ahead of normal for most of the prairies (Figs. 2). Models suggest that bertha armyworm pupal development in Alberta is 10-14 days faster than average development for this time of year. There are small areas in Alberta where the model predicts that pupal development may be greater than 90% completed.
Where bertha armyworm are present, adults may be appearing in areas where predicted pupal development is greater than 90% complete. We suggest that bertha armyworm traps should be installed as soon as possible. Many thanks to all of the volunteers across the Prairie region who are hosting BAW pheromone traps in 2023!
Visit the Alberta Insect Pest Monitoring Network page for information about insect 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 first Manitoba Crop Pest Update for 2023 was posted on May 24. Watch their website for new Crop Pest Updates as the season continues and check out the archives to read past Updates.
As crops are beginning to pop up – so is the pea leaf weevil (Sitona lineatus). Adults emerge in the spring and feed on legumes, such as field peas, faba beans, alfalfa, beans and lentils (causing characteristic “notching” or “scalloping” on the edges of leaves) before laying their eggs in field peas and faba beans. Each adult female can lay over 300 eggs in one summer! The eggs hatch in the soil near developing plants and larvae move to feed on nitrogen-fixing nodules. This results in partial or complete inhibition of nitrogen fixation by the plant, causing poor plant growth. Feeding by adults on the foliage and by larvae on the root nodules contributes to yield losses in field pea and faba bean crops.
The pea leaf weevil is a slender greyish-brown beetle measuring approximately 5 mm in length. These insects can be distinguished by three light-coloured stripes extending length-wise down the thorax and the abdomen. All species of Sitona, including the pea leaf weevil, have a short or ‘broad’ snout unlike species like the cabbage seedpod weevil that have a long, curved snout. Mature larvae grow up to 3.5-5.5 mm long. The larvae are legless and c-shaped with a brown head.