Welcome to Week 4 for the 2025 growing season! This week includes: • Weather synopsis • Wireworms • Cutworms • Flea beetles • Alfalfa weevil • Cereal leaf beetle • Pea leaf weevil • Grasshopper diversity and scouting • Diamondback moth • Bertha armyworm • Cabbage seedpod weevil • Provincial insect pest report links • Crop report links • Previous posts
Catch Monday’s Insect of the Weekfor Week 4 – This year features lesser-known insect pest species to help producers remain vigilant! Learn more about the Cabbage stem flea beetle!
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, Meghan Vankosky and Jennifer Otani
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Week 4
The weekly average temperature for May 19 – May 25, 2025, across the Prairies was 11 °C which is slightly warmer than the long-term average. Temperatures were warmest in northern Alberta and coolest in southeastern Saskatchewan, southwestern Manitoba, and the east of the Rockies in Alberta (Figure 1). Overall, growing season average temperatures continue to climb as the first week of June approaches (Figure 2).
Figure 1. Seven-day average temperature (°C) observed across the Canadian prairies for the period of May 19-25, 2025.Figure 2. Growing season average temperature (°C) observed across the Canadian prairies for the period of April 1-May 25, 2025.
Between May 19 – 25, 2025, the prairie region received rain, starting on Victoria Day. Unfortunately, rainfall amounts generally did not exceed 15 mm (Figure 3). Edmonton and the southwest surrounding areas of Alberta (e.g., Yellowhead, Lac St. Anne, Brazeau, Parkland, Leduc, Lacombe, and Wetaskiwin Counties) received the greatest rainfall over the past week, whereas other areas of the Canadian prairies recorded less than 15 mm (Figure 3). So far this growing season, the majority of the prairie growing region has received an accumulation of less than 100 mm of cumulative rainfall between April 1 and May 25, 2025; Figure 4).
Figure 3. Seven-day average precipitation (mm) observed across the Canadian prairies for the period of May 19-25, 2025.Figure 4. Growing season cumulative rainfall (mm) observed across the Canadian prairies for the period of April 1-May 25, 2025.
Active Wildfires – Natural Resources Canada’s Canadian Wildland Fire Information System (CWFIS) creates and updates daily fire weather and fire behaviour maps year-round with hot spot maps updated daily between May and September. The website features three types of maps plus valuable links. Maps to access include: • Fire Weather • Fire Behaviour • Fire M3 Hotspotand example of the map for May 29, 2025, is copied below (Fig. 1).
Persons outdoors performing field scouting need to be aware of air quality arising from wildfire activity. Two online resources are available – both are updated daily and provide short video clips of forecasted ground level smoke conditions: • FireSmoke.ca (link to snip of short forecast video retrieved May 29, 2025 or Figure 2 for examples). • Firework (link to snip of forecast video retrieved May 29, 2025 or Figure 3 for examples).
Haley Catton, Wim van Herk, Julien Saguez and Jennifer Otani
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Week 4
Wireworms are the larval stage of click beetles from the family Elateridae. Click beetles, the adult stage, do not cause damage to crops. Wireworms live in the soil, where it can take 4 or more years to complete larval development. In the soil, wireworms feed on germinating seeds and the roots of a wide variety of prairie field crops including cereals, pulses, oilseeds, and vegetables including potato and carrots. Damage to root vegetables can result in unmarketable produce.
Several species of wireworms can be found on the Canadian Prairies but species commonly occurring in field crops are included in Figure 1. Even more importantly, there are four primary pest species, including Hypnoidus bicolor, prairie grain wireworm (Selatosomus aeripennis destructor), sugarbeet wireworm (Limonius californicus), and flat wireworm (Aeolus mellillus).
Figure 1. Dorsal views of economically important species of wireworms observed across the Canadian prairies and their adult click beetle. (Source: Guide to Pest Wireworms in Canadian Prairie Field Crop Production).
Similar to cutworms, bare patches in a field can be an early and obvious sign of wireworm infestation in the spring. Patchy crop emergence (Fig. 2), results when wireworms consume germinating seeds or feed on the roots and stems of young seedlings (Fig. 3).
Figure 2. A cereal field with patchy seedling emergence and stand establishment due to wireworm infestation. Picture by Dr. Haley Catton (AAFC, Lethbridge).Figure 3. Wireworm feeding damage on a faba bean seedling. Picture by Chris Baan.
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.
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.
Jennifer Otani, James Tansey, Dan Johnson and John Gavloski
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Week 4
Prairie-Wide Monitoring: Annual grasshopper surveying is performed across western Canada by visually estimating densities in late summer. Review the prairie-wide historical survey maps for this insect species. Review the PPMN monitoring protocol although the provinces of Alberta, Saskatchewan, and Manitoba have specific survey protocols for their respective network cooperators. Commercial fields where comparatively higher densities of pest species of grasshoppers were observed in 2024 are highlighted yellow, orange, or red in the geospatial map featured in Figure 1. Areas where historically higher densities of grasshoppers were observed in 2024 are worth prioritizing in 2025.
Figure 1. Densities of grasshoppers observed by visual in-field observations in late summer of 2024.
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.
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, John Gavloski and Meghan Vankosky
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Week 4
The annual pea leaf weevil survey is underway! 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, Kristen Guelly, Jennifer Retzlaff, Adele Beaudoin, Boyd Mori and Julie Soroka
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Week 4
The larval stage of this weevil feeds on alfalfa leaves in a manner that characterizes the pest as a “skeletonizer” (Fig. 1). The green larva features a dorsal white line down the length of its body, has a dark brown head capsule, and will grow to 9 mm long.
Figure 1. Developmental stages of the alfalfa weevil (Hypera postica). Composite image: J. Soroka (AAFC-Saskatoon).
Alfalfa growers are encouraged to check an updated Protocol for Monitoring Alfalfa Weevil prepared by Guelly et al. 2025. Additional information can be accessed by reviewing the Alfalfa Weevil Page extracted from the “Field crop and forage pests and their natural enemies in western Canada – Identification and management field guide” (2018; accessible in either English-enhanced or French-enhanced versions).
There is one generation of cabbage seedpod weevil (CSPW; Ceutorhynchus obstrictus) per year. The overwintered adult is an ash-grey weevil measuring 3-4mm long (Fig. 1; left photo). Mating and oviposition are quickly followed by eggs hatching within developing canola pods (Fig. 1; right photo). The highly concealed larvae feed within the pod, consuming the developing seeds.
Figure 1. Cabbage seedpod weevil (left) and egg dissected from within a canola pod (right). Photos: the late Dr. Lloyd Dosdall.
Damage: Adult feeding damage to buds is more evident in dry years when canola is unable to compensate for bud loss. Adults mate following a pollen meal then the female will deposit a single egg through the wall of a developing pod or adjacent to a developing seed within the pod (Fig. 1; right photo). Eggs are oval and an opaque white, each measuring ~1mm long. Typically, a single egg is laid per pod although, when CSPW densities are high, two or more eggs may be laid per pod.
There are four larval instar stages of the CSPW and each stage is white and grub-like in appearance ranging up to 5-6mm in length (Fig. 2; left photo). The first instar larva feeds on the cuticle on the outside of the pod while the second instar larva bores into the pod (Fig. 2; right photo, lower pod), feeding on the developing seeds. A single larva consumes about 5 canola seeds. The mature larva chews a small, circular exit hole (Fig. 2; right photo, upper pod) from which it drops to the soil surface and pupation takes place in the soil within an earthen cell. Approximately 10 days later, the new adult emerges to feed on maturing canola pods. Later in the season, these new adults migrate to overwintering sites beyond the field.
Figure 2. Larva feeding amongst developing seeds within canola pod (left) and larval entrance hole (right photo, lower pod) compared to mature larval exit hole (right photo, uppower pod). Photos: the late Dr. Lloyd Dosdall.
Prairie-Wide Monitoring: The annual cabbage seedpod weevil survey is performed in canola at early flower stages using sweep-net collections. Review the prairie-wide historical survey maps for this insect species. Review the PPMN monitoring protocol although the provinces of Alberta, Saskatchewan, and Manitoba have specific survey protocols for their respective network cooperators. Commercial fields where comparatively higher densities of adult cabbage seedpod weevils were observed in 2024 are highlighted yellow, orange, or red in the geospatial map featured in Figure 3. Areas where historically higher densities of cabbage seedpod weevil were observed in 2024 are worth prioritizing in 2025.
Figure 3. Densities of cabbage seedpod weevil (Ceutorhynchus obstrictus) observed in sweep-net samples retrieved from commercial fields of canola (Brassica napus) grown in Saskatchewan, Alberta, and the British Columbia portion of the Peace River region in 2024.
In-Field Monitoring:
Begin sampling when the crop first enters the bud stage and continue through the flowering.
Sweep-net samples should be taken at ten locations within the field with ten 180° sweeps per location.
Count the number of weevils at each location. Samples should be taken in the field perimeter as well as throughout the field.
Adults will invade fields from the margins and if infestations are high in the borders, application of an insecticide to the field margins may be effective in reducing the population to levels below which economic injury will occur.
An insecticide application is recommended when three to four weevils per sweep are collected and has been shown to be the most effective when canola is in the 10 to 20% bloom stage (2-4 days after flowering starts).
Consider making insecticide applications late in the day to reduce the impact on pollinators. Whenever possible, provide advanced warning of intended insecticide applications to commercial beekeepers operating in the vicinity to help protect foraging pollinators.
High numbers of adults in the fall may indicate the potential for economic infestations the following spring.
Albertan growers can report field observations and check the live map for CSPW posted by Alberta Agriculture and Irrigation (screenshot provided below as an example; retrieved 2022Jul28 but will be updated with 2025 reports as season progresses).
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.
Jennifer Otani, Jonathon Williams, Meghan Vankosky, John Gavloski, Carter Peru, James Tansey and Shelley Barkley
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Week 4
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 25, there are no areas on the prairies that have surpassed 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 from April 1 to May 25, 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. Cumulative counts from sentinel pheromone monitoring sites targeting bertha armyworm moths across the Canadian prairies in 2024 are highlighted as geospatial areas where producers are encouraged to prioritize in-field monitoring in 2025. Areas in Figure 2 highlighted yellow, orange, or especially red hosted pheromone traps that intercepted relatively high cumulative counts of moths in 2024 and should be prioritized for in-field scouting in 2025. Review the prairie-wide historical survey maps for this insect species.
Figure 2. Cumulative weekly counts of Bertha armyworm (Mamestra configurata) moths arising from the 2024 growing season.
Figure 3 includes photos of the various life stages of the bertha armyworm. There is one generation per year and pupae overwinter in the soil (Fig. 3, 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 3. 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!
Jennifer Otani, John Gavloski, James Tansey, Carter Peru, Shelley Barkley and Amanda Jorgensen
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Week 4
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 26, 2025 issue includes notification that pea leaf weevil survey has begun, continued flea beetle pressure and need to monitor seedling canola plus mustard, continuation of cutworm monitoring (and link to live cutworm map). • 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 derived from weekly data are available so refer to the Live Map! • Diamondback moth pheromone trap live monitoring map for AB – Cumulative counts derived from weekly data are now being generated so refer to the Live map.
