Welcome to Week 3 for the 2025 growing season! This week includes: • Weather synopsis • Flea beetles • Cutworms • Cereal leaf beetle • Pea leaf weevil • Grasshopper diversity and scouting • Diamondback moth • Bertha armyworm • Tick tips • Access PPMN-approved field guides • Crop production guide links • Provincial insect pest report links • Crop report links • Previous posts
Catch Monday’s Insect of the Weekfor Week 3 – This year features lesser-known insect pest species to help producers remain vigilant! Learn more about the Brown marmorated stink bug!
Questions or problems accessing the contents of this Weekly Update? Please contact us so we can connect you to our information. Past “Weekly Updates” can be accessed on our Weekly Update page.
Dylan Sjolie, Tamara Rounce, Jennifer Otani and Meghan Vankosky
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Week 3
Growing season temperatures cooled off slightly between May 12 and May 18, bringing the 7-day average temperature close to the long-term climate normals average for this time of the month (Fig. 1). The weekly average temperature for May 12 – May 18, 2025, across the Prairies was 10 °C. Temperatures were warmest in southeast Manitoba and cooler around the MB/SK border and the foothills region of Alberta (Figure 2).
Figure 1. Seven-day average temperature (°C) observed across the Canadian prairies for the period of May 12-18, 2025.Figure 2. Growing season average temperature (°C) observed across the Canadian prairies for the period of April 1-May 18, 2025.
The southeast corner of Saskatchewan and southwest corner of Manitoba received a good amount of rainfall over the past week, whereas other areas remained relatively dry (Fig. 3). As of May 18, a large portion of the prairie agricultural area has received less than 100 mm of cumulative rainfall this growing season (cumulative rainfall between April 1 and May 18; Fig. 4).
Figure 3. Seven-day average precipitation (mm) observed across the Canadian prairies for the period of May 12-18, 2025.Figure 4. Growing season cumulative rainfall (mm) observed across the Canadian prairies for the period of April 1-May 18, 2025.
Flea Beetles (Chrysomelidae: Phyllotreta species) – Be on the lookout for flea beetle damage resulting from feeding on canola cotyledons but also on the stem. Two species, Phyllotreta striolata and P. cruciferae, will feed on all cruciferous plants but they can cause economic levels of damage in canola during the seedling stages.
Figure 1. Flea beetle feeding inflicted by overwintered adults including ‘shot-hole’ and stem feeding on seedling canola (B. napus). Photos: AAFC-Beaverlodge-Otani
Remember, the Action Threshold for flea beetles on canola is 25% of cotyledon leaf area consumed. Watch for shot-hole feeding in seedling canola but also watch the growing point and stems of seedlings which are particularly vulnerable to flea beetle feeding.
If flea beetle densities are high, seedling damage levels can advance quickly – even within the same day! The cotyledon stage of canola is vulnerable to flea beetle feeding.
Estimating flea beetle feeding damage can be challenging. Using a visual guide to estimate damage can be helpful. Use the two images (copied below for reference) produced by Dr. J. Soroka (AAFC-Saskatoon) to help estimate percent of leaf area consumed for canola seedlings – take Figures 2 and 3 scouting!
Figure 2. Canola cotyledons with various percentages of leaf area consume owing to flea beetle feeding damage (Photo: Soroka & Underwood, AAFC-Saskatoon).Figure 3. Percent leaf area consumed by flea beetles feeding on canola seedlings (Photo: Soroka & Underwood, AAFC-Saskatoon).
Flea beetles were the Insect of the Week (Wk 02 – May 13, 2024)! Additionally, access biological and pest management information posted by Saskatchewan Agriculture, or Manitoba Agriculture and Resource Development, or the Canola Council of Canada’s Canola Encyclopedia. Refer to the flea beetle page within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018), accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Cutworm scouting spans April to late June across the Canadian prairies! Scout fields that are “slow” to emerge, are missing rows, include wilting or yellowing plants, have bare patches, or appear highly attractive to birds – these are areas warranting a closer look. Plan to follow up by walking these areas either very early or late in the day when some cutworm species (or climbing cutworms) move above-ground to feed. Start to dig below the soil surface (1-5 cm deep) near the base of symptomatic plants and also any healthy plants immediately adjacent to missing rows or wilting or clipped plants. Some cutworms feed while remaining just below the soil surface, clipping then pulling the plant below the soil surface as they munch away! If the plant is well-established (e.g., perennial grass or legume), check within the crown plus in the adjacent soil. The culprits could be cutworms, wireworms, or more!
Important: Several species of cutworms (Lepidoptera: Noctuidae) can be present in fields. They range in colour from shiny opaque, to tan, to brownish-red with chevron patterning. A field guide is available to help growers scout and manage the various species of cutworms that can appear in field crops grown on the Canadian prairies. Cutworm Pest of Crops is available free in either English or French! Download a searchable PDF copy to access helpful diagnostic photos plus a table showing which larvae are active at different points in the growing season!
Other vital resources to scout and manage cutworms include:
● For anyone on the Canadian prairies, Manitoba Agriculture’s Cutworms in Field Crops fact sheet includes suggested nominal thresholds for cutworms in several crops (Table 1). The same fact sheet describes important biological information, and provides great cutworm photos to support in-field scouting!
● For Albertans….. If you find cutworms, please consider using the Alberta Insect Pest Monitoring Network’s “2025 Cutworm Reporting Tool” then view the live 2025 cutworm map updated daily. Review the live map to see where cutworms are appearing then prioritize in-field scouting accordingly.
The cereal leaf beetle (Chrysomelidae: Oulema melanopus) has a broad host range. Wheat is the preferred host, but adults and larvae also feed on leaf tissue of oats, barley, corn, rye, triticale, reed canarygrass, ryegrass, fescue, wild oats, millet and other grasses. Yield quality and quantity is decreased, if the flag leaf is stripped. Fun fact: Cereal leaf beetle larvae carry their own fecal waste above their body to help protect themselves from predators.
Fortunately, the parasitoid wasp, Tetrastichus julis Walker (Hymenoptera: Eulophidae), is an important natural enemy of cereal leaf beetle larvae. Learn more about this beneficial insect species featured in Week 9 of 2023’s Insect of the Week!
Cereal Leaf Beetle Lifecycle and Damage:
Adult: Adult cereal leaf beetles (CLB) have shiny bluish-black wing covers (Fig. 1). The thorax and legs are light orange-brown. Females (4.9 to 5.5 mm) are slightly larger than males (4.4 to 5 mm). Adult beetles overwinter in and along the margins of grain fields in protected places such as in straw stubble, under crop and leaf litter, and in the crevices of tree bark. They favour sites adjacent to shelterbelts, deciduous and conifer forests. They emerge in the spring once temperatures reach 10-15 ºC and the adults are active for about 6 weeks. They usually begin feeding on grasses, then move into winter cereals and later into spring cereals.
Figure 1. Adult Oulema melanopus measure 4.4-5.5 mm long (Photo: M. Dolinski).
Egg: Eggs are laid approximately 14 days following the emergence of the adults. Eggs are laid singly or in pairs along the midvein on the upper side of the leaf and are cylindrical, measuring 0.9 mm by 0.4 mm, and yellowish in colour. Eggs darken to black just before hatching.
Larva: The larvae hatch in about 5 days and feed for about 3 weeks, passing through 4 growth stages (instars). The head and legs are brownish-black; the body is yellowish. Larvae are usually covered with a secretion of mucus and fecal material, giving them a shiny black, wet appearance (Fig. 2). When the larva completes its growth, it drops to the ground and pupates in the soil.
Figure 2. Larval stage of Oulema melanopus with characteristic feeding damage visible on leaf (Photo: M. Dolinski).
Pupa: Pupal colour varies from a bright yellow when it is first formed, to the colour of the adult just before emergence. The pupal stage lasts 2 – 3 weeks. Adult beetles emerge and feed for a couple of weeks before seeking overwintering sites. There is one generation per year.
Access scouting tips for cereal leaf beetle or find more detailed information by accessing the Oulema melanopus page from the “Field crop and forage pests and their natural enemies in western Canada – Identification and management field guide” (2018; accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Jennifer Otani, Jonathon Williams and Meghan Vankosky
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Week 3
The annual pea leaf weevil survey is getting started! The survey is conducted by counting the characteristic ‘u’ shaped feeding notches made by adult pea leaf weevil at several locations along the field edge (Fig. 1).
Figure 1. Examples of adult pea leaf weevil damage on field pea seedlings, (A) seedling with notches on all nodes, (B) stereotypical crescent-shaped notches on the leaf margin, (C) clam or terminal leaf of the pea seedling with arrows indicating the feeding notches. All photos courtesy of Dr. L. Dosdall.
In the spring, overwintered adults disperse to feed upon the leaf margins and growing points of legume seedlings (alfalfa, clover, dry beans, faba beans, peas). This feeding can produce a characteristic, scalloped (or notched) edges (Fig. 2). Females lay their eggs in the soil either near or on developing pea or faba bean plants from May to June.
Figure 2. Adult pea leaf weevil feeding and creating characteristic “notch” at edge of faba bean leaf. Photo: AAFC-Saskatoon-Williams.
The annual pea leaf weevil survey is conducted from late May to early June. The survey is conducted by counting the characteristic ‘u’ shaped feeding notches made by adult pea leaf weevil at several locations along the field edge. Review the prairie-wide historical survey maps. Higher levels of feeding damage are correlated to higher pea leaf weevil densities so areas highlighted in Figure 3 warrant in-field monitoring in the spring of 2025.
Figure 3. Results of the annual pea leaf weevil survey conducted in the spring of 2024.
Biological and monitoring information related to pea leaf weevil in field crops is posted by the province of Alberta and in the PPMN monitoring protocol. Access the Pea leaf weevil information posted by the Manitoba Pulse & Soybean Growers, Saskatchewan Agriculture, Alberta Agriculture and Irrigation, or the Prairie Pest Monitoring Network. Also refer to the pea leaf weevil page within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018), accessible as a free downloadable PDF in either English or French on our Field Guides page.
Jennifer Otani, James Tansey, Dan Johnson, Jonathon Williams and John Gavloski
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Week 3
Grasshopper Scouting Tips: ● Review grasshopper diversity and photos of nymphs, adults, and non-grasshopper species (Gavloski, Williams, Underwood, Johnson, Otani) to aid with field scouting from egg hatch and onwards. The PDF includes photos to help differentiate native versus pest grasshopper species plus froghopper, treehopper or even katydid species. ● It is best to scout on warm days when grasshopper nymphs are more active and easier to observe. ● Carefully check roadside ditches and along field edges but also check the edge of the crop and into the actual field. ● Younger or earlier instar nymphs are easier to manage – visit sites every few days to stay on top of local field conditions. ● A sweep-net can ‘detect’ grasshopper nymphs, however, economic thresholds for grasshoppers are based on the number of grasshoppers per square-metre counts. ● Access the PPMN’s Grasshopper Monitoring Protocol as a guide to help implement in-field monitoring. ● Review grasshopper lifecycle, damage and scouting and economic thresholds to support sound management decisions enabling the preservation of beneficial arthropods and mitigation of economic losses.
Important – A preliminary summary of available thresholds for grasshoppers has been kindly shared by Dr. J. Tansey (Saskatchewan Agriculture) in Table 1. When scouting, compare in-field counts to the available threshold value for the appropriate host crop AND for field or ditch situations. Available thresholds (nominal and economic) help support producers while protecting beneficials (i.e., predators, parasitoids, and pathogens) that regulate natural populations of grasshoppers.
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. 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 and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Spring Pheromone Trap Monitoring of Adult Males: Across the Canadian prairies, spring monitoring is initiated to acquire weekly counts of adult moths (Fig. 1) attracted to pheromone-baited delta traps deployed in fields. Weekly trap interceptions are observed to generate cumulative counts. These cumulative count estimates are broadly categorized to help producers prioritize and time in-field scouting for larvae.
Figure 1. Adult diamondback moth.
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 (Fig. 2) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
Figure 2. Diamondback larva measuring ~8mm long. Note brown head capsule and forked appearance of prolegs on posterior.
The economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1 m² (approximately 2-3 larvae per plant). Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1 m² (approximately 1-2 larvae per plant).
Figure 3. Diamondback moth pupa within silken cocoon.
Please refer to this week’s Provincial Insect Pest Report Links to find the most up-to-date information summarizing weekly cumulative counts compiled by provincial pheromone trapping networks across the Canadian prairies in 2025.
Degree-days can be used to predict the timing of insect development and plan for pest scouting and management. Degree-days are calculated for different insect species using temperature thresholds specific to their development. Based on research, the temperature threshold for bertha armyworm (Mamestra configurata) development is 7 °C and 352 accumulated degree-days (base 7 °C) are required for overwintered pupae to begin their spring development phase. As of May 18, much of the prairies has not reached the degree-day requirement for pupal development of bertha armyworm (Fig. 1).
Figure 1. Growing degree-day heat units (Base 7 °C) accumulated across the Canadian prairies as of May 18, 2025.
Pheromone traps used to monitor bertha armyworm are typically set up along canola fields when pupal development reaches 75-80%; the 2024 monitoring season started the week of June 10, 2024.
Figure 2 includes photos of the various life stages of the bertha armyworm. There is one generation per year and pupae overwinter in the soil (Fig. 2, C). Each growing season, green unitraps utilizing pheromone lures are deployed and checked weekly over a 6-week window. Cumlative counts generated from the pheromone traps are used to estimate subsequent bertha armyworm densities. The cumulative moth count data is compiled using geospatial maps then posted to support and time in-field scouting for damaging populations of larvae by mid-July through to August.
Figure 2. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).
Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page. Also consider reviewing the 2019 Insect of the Week which featured bertha armyworm and its doppelganger, the clover cutworm!
Reminder – When field scouting, avoid unwanted passengers – remember to watch for ticks at this time of year!
Blacklegged (deer) ticks can carry Lyme Disease, anaplasmosis, babesiosis, or Powassan virus. Access tick information plus how to safely remove and identify a tick provided by Health Canada which also recommends these “before you go” ways to help prevent tick bites: • light coloured, long-sleeved shirts and pants help you spot ticks easier. • tuck shirt bottoms into pants and pant cuffs into socks – seal yourself in and ticks out! • closed-toe shoes keep ticks out! • apply an insect repellent containing DEET or Icaridin to clothing and exposed skin (according to product label directions). • wear permethrin-treated clothing (according to product label direction). …. and review the full set of helpful tips!
Public Health Agency of Canada has a Top 10 Tick Hiding Spots on Your Body available as a poster in multiple languages including Mi’kmaq, Mohawk, Ojibwe (Eastern), French, English, Spanish, Tagalog, Arabic, Punjabi, Chinese (simplified and traditional), and Italien. An example in English is posted below for your quick reference (Fig. 1) so check it, then yourself, and your pets!
Figure 1. Screenshot of Public Health Agency of Canada’s infographic of top 10 tick hiding spots on your body (2020; retrieved 2024May23).
Another good resource is the free eTick APP which is a public platform for image-based identification and population monitoring of ticks in Canada. Both Google Play and iOS versions of the App enable users to upload tick photos for help with identification.
Continued surveillance is important and enables tracking of Lyme disease incidence and risk. Follow the links to learn more about Lyme disease and ticks if you live in British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, or Quebec. Access additional information posted by Health Canada related to Lyme disease surveillance which also summarized a preliminary 2024 total of 5239 cases of Lyme disease were reported to provincial public health units across Canada.
In addition to being free, the downloadable PDF versions of these guides are searchable. All include descriptions of insect biology, helpful diagnostic photos, plus tips related to when and how to scout for important economic pests of western Canada’s many field crops.
Here’s one of the five guides we highly recommend but there’s also guides for wireworm pest species, cutworm pest species, cow patty insects plus the pests & predators field guide! Find them all here to download!
Every year, these guides are updated with product information and so much more! Hard copies can be purchased via the above websites but also look for the download button to access FREE downloadable PDF copies!
A few other helpful tools to keep at your finger tips:
Jennifer Otani, Shelley Barkley, Amanda Jorgensen, James Tansey and Carter Peru
Categories
Week 3
Prairie-wide provincial entomologists provide insect pest updates throughout the growing season. Follow the hyperlinks to access their information as the growing season progresses:
ALBERTA’SInsect Pest Monitoring Network webpage links to insect survey maps, live feed maps, insect trap set-up videos, and more. There is also a Major Crops Insect webpage. Remember AAF’s Agri-News includes insect-related information: • May 20, 2025 issue includes a recommendation to scout for grasshoppers, an update on flea beetle risk, and notice that diamondback moth reporting has begun. Also, AAI staff members have started surveying for pea leaf weevil in southern Alberta this week. • Cutworm live monitoring map for AB – Cumulative counts arising from weekly data are available so refer to the Live Map which already cites 2025 reports! • Diamondback moth pheromone trap live monitoring map for AB – Cumulative counts arising from weekly data are now being generated so refer to the Live map.
As the growing season progresses, the Weekly Update topics move on and off the priority list for in-field scouting. We provide the list below to support season-long monitoring. Click to review these earlier 2025 Posts (organized alphabetically): • 2024 Risk maps (Wk 02) • Field heroes (Wk 02) • Scouting charts – canola and flax (Wk 03 of 2022)
