Weekly Update

Week 13 and many of our staff are occupied elsewhere! This week, the unbelievable warm weather continues to advance both insect and plant development. Take a peak at how many days various areas of the prairies have experienced >25 °C compared to >30 °C! Some areas of the prairies are harvesting silage and preparing to harvest their grain.

Be sure to catch the Insect of the Weekit’s wheat stem sawfly!

Stay safe and good scouting to you!

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.

Weather synopsis

TEMPERATURE: This week, staff are occupied elsewhere and unable to generate the full weather synopsis. The growing degree day (GDD) maps for Base 5 ºC and Base 10 ºC (April 1-July 26, 2021) can be viewed by clicking the hyperlinks. Over the past 7 days (July 22-28, 2021), the lowest temperatures recorded across the Canadian prairies ranged from < 0 to >14 °C while the highest temperatures observed ranged from <20 to >36 °C. Again, the incredible heat experienced is contributing to those heat units – check the number of days of >25 °C or >30 °C across the Canadian prairies (April 1-July 28, 2021).

PRECIPITATION: This past week (July 22-28, 2021), rainfall was reported in the far north of the Alberta side of the Peace River region, in central Alberta, the northwest and southeast of Saskatchewan, and in the northwest and far southeast of Manitoba yet the vast majority of the prairies’ arable acres recieved scant to no rain (Fig. 1). Rainfall amounts for the period of June 27 – July 28 (30-day accumulation) are represented in Figure 2. Precipitation for the growing season has been less than average across most of the prairies (Fig. 3).

Figure 1. Accumulated precipitation (mm) observed across the Canadian prairies the past 7 days (July 22-28, 2021).
Image has not been reproduced in affiliation with, or with the endorsement of the Government of Canada and was retrieved (29Jul2021). Access the full map at https://www.agr.gc.ca/DW-GS/current-actuelles.jspx?lang=eng&jsEnabled=true
Figure 2. Accumulated precipitation (mm) observed across the Canadian prairies the past 30 days (June 27 – July 28, 2021).
Image has not been reproduced in affiliation with, or with the endorsement of the Government of Canada and was retrieved (29Jul2021). Access the full map at https://www.agr.gc.ca/DW-GS/current-actuelles.jspx?lang=eng&jsEnabled=true
Figure 3. Accumulated precipitation (mm) observed across the Canadian prairies for the growing season (April 1 – July 28, 2021).
Image has not been reproduced in affiliation with, or with the endorsement of the Government of Canada and was retrieved (29Jul2021). Access the full map at https://www.agr.gc.ca/DW-GS/current-actuelles.jspx?lang=eng&jsEnabled=true

The maps above are all produced by Agriculture and Agri-Food Canada. Growers can bookmark the AAFC Current Conditions Maps for the growing season. Historical weather data can be access at the AAFC Drought Watch Historical website, Environment Canada’s Historical Data website, or your provincial weather network.

Prairie-wide survey of stored grain pests

Scientists are looking for volunteers to help conduct a survey of stored grain pests on the Canadian Prairies. The goals of this survey are to:
1) detect potentially new invasive grain pests to the area,
2) know the nature of the insect species currently occurring in farm grain bins,
3) determine the prevalence of those species, and 4) determine the conditions under which these species occur.

The data collected will help assess current and future threats to the grain supply on the Canadian Prairies and help focus research efforts. Producers willing to participate will be notified of the results obtained on their farm, as well as the results of the overall survey.

This rusty grain beetle, Cryptolestes ferrugineus (Stephens), resting on a wheat kernel, measures ~2 mm in length. Photo: Canadian Grain Commission (retrieved 28Jul2021 from https://grainscanada.gc.ca/en/grain-quality/manage/identify-an-insect/primary-insect-pests/rusty-grain-beetle.html).

The survey involves a minimal amount of input for participants: Two grain probe traps are inserted into grain from the top, removed 2 to 4 weeks later, their contents emptied into 2 vials, then the vials containing the samples are mailed with a datasheet providing information about the conditions under which the grain was stored. The traps can be placed in grain from last year’s harvest, this year’s harvest, or into animal feed since many grain species also occur in animal feed. Participants will be mailed the two grain probe traps and two sampling vials plus an envelope with pre-paid postage will be provided for returning the samples. All information collected about the farm will remain strictly confidential.

Please contact Vincent Hervet (AAFC stored product entomologist) at vincent.hervet@agr.gc.ca, if you are willing to contribute to this survey.

Fuzzy white “eggs” on wheat or barley heads?

As wheat and barley fields continue to mature, fuzzy, white “egg-like” clusters may be observed (Fig. 1). Sometimes a dead caterpillar can be found alongside the fuzzy cluster. These white “egg-like” clusters are yet another species of @FieldHeroes! Cotesia parasitoid wasp cocoons arise from parasitoid larvae that develop within a single lepidopteran caterpillar then the parasitoid larvae burst out through the host’s body wall – in this case, likely from a wheat head armyworm (Dargida diffusa). Researchers are seeking intact parasitoid cocoons in order to learn what species of Cotesia is parasitizing the wheat head armyworm.

Figure 1. Fuzzy egg-like clusters which are Cotesia cocoons enclosing developing pupae. Photo: AAFC-Saskatoon T. Wist.

Request for help: If you find intact samples (i.e., developing Cotesia still within cocoons but NOT open as in Fig. 2), please contact Tyler.Wist@agr.gc.ca to arrange collection and shipping of the cocoons and any associated lepidopteran caterpillars. Remember, intact cocoons NOT with open ends are needed.

Figure 2. Empty Cotesia cocoons recently vacated by adult parasitoid wasps. Photo: AAFC-Saskatoon T. Wist.

Pre-Harvest Intervals (PHI)

Before the harvest rush begins, start to consider pre-harvest intervals. The PHI refers to the minimum number of days between a pesticide application and swathing or straight combining of a crop.  The PHI recommends sufficient time for a pesticide to break down. PHI values are both crop- and pesticide-specific.  Adhering to the PHI is important for a number of health-related reasons but also because Canada’s export customers strictly regulate and test for the presence of trace residues of pesticides.

Here are a few resources to help:
• Information about PHI and Maximum Residue Limits (MRL) is available on the Keeping It Clean website.
• The Pest Management Regulatory Agency has a fact sheet, “Understanding Preharvest Intervals for Pesticides” or download a free PDF copy.
• Use Keeping It Clean’s “Spray to Swath Interval Calculator” to accurately estimate:
◦ PHI for canola, chickpeas, lentils, faba beans, dry beans, or peas.
◦ How long to wait, if the crop’s already been sprayed.
◦ To find a pesticide to suit your timeline.
• Provincial crop protection guides include the PHI for every pesticide x crop combination; Alberta, Saskatchewan, or Manitoba guides are downloadable as free, searchable PDF format.

West nile virus risk

The following is offered to help predict when Culex tarsalis, the vector for West Nile Virus, will begin to fly across the Canadian prairies. This week, regions most advanced in degree-day accumulations for Culex tarsalis are shown in Figure 1 but the unusual heat across the prairies greatly accelerated mosquito development!

As of July 25, 2021 (Fig. 1), C. tarsalis development has now reached the point that adults are predicted to be flying across the south of the prairies from Manitoba to Alberta. Outdoor enthusiasts falling within areas highlighted red (i.e., areas that have accumulated sufficient heat accumulation for C. tarsalis to emerge) should wear DEET to protect against WNV! Because of the continued high temperatures, areas highlighted yellow or orange in the map below (as of July 25) should also start to use DEET this week! IF C. tarsalis is present in an area where WNV is active, it may take as little as 14 days for adults to become fully infective with the current warm weather (Fig. 2).

Figure 1. Predicted development of Culex tarsalis across the Canadian prairies (as of July 25, 2021).
Figure 2. Predicted days for virulence of West Nile Virus to develop within Culex tarsalis, if present within a region (as of July 26, 2021).

The Public Health Agency of Canada posts information related to West Nile Virus in Canada and also tracks West Nile Virus through human, mosquito, bird and horse surveillance. Link here to access their most current weekly update (reporting date June 21, 2021; retrieved July 29, 2021). The screenshot below (retrieved 29Jul2021) serves as a reference and reports one human case of WNV, a positive wild bird, and positive mosquito pools in Ontario.

Bird surveillance continues to be an important way to detect and monitor West Nile Virus. The Canadian Wildlife Health Cooperative (CWHC) works with governmental agencies (i.e., provincial laboratories and the National Microbiology Laboratory) and other organizations to report the occurrence of WNV. Dead birds retrieved from areas of higher risk of West Nile Virus are tested for the virus. A screenshot of the latest reporting results posted by Canadian Wildlife Health Cooperative is below (retrieved 29Jul2021).

Anyone keen to identify mosquitoes will enjoy this pictorial key for both larvae and adults which is posted on the Centre for Disease Control (CDC) website but sadly lacks a formal citation other than “MOSQUITOES: CHARACTERISTICS OF ANOPHELINES AND CULICINES prepared by Kent S. Littig and Chester J. Stojanovich” and includes Pages 134-150. The proper citation may be Stojanovich, Chester J. & Louisiana Mosquito Control Association. (1982). Mosquito control training manual. pp 152.

Provincial insect pest report links

Provincial entomologists provide insect pest updates throughout the growing season so link to their information:

MANITOBA’S Crop Pest Updates for 2021 are now available – access the July 28, 2021 report here. Be sure to bookmark their Crop Pest Update Index to readily access these reports! Bookmark their insect pest homepage to access fact sheets and more!
Bertha armyworm pheromone trap monitoring update for MB – Cumulative counts arising from weekly data are available here. Cumulative counts are categorized as “low risk” so far (i.e., 0-300 moths).
Diamondback moth pheromone trap monitoring update for MB – Trapping has drawn to a close for 2021. Access the summary here. Only 65 traps intercepted moths and the highest cumulative count was 171 moths near Selkirk. Access the summary (as of June 30, 2021). At this point, in-field scouting for larvae remains important.

SASKATCHEWAN’S Crop Production News is available. Access Issue #4 online which includes a crop protection lab update, and describes thrips in cereals. Be sure to bookmark their insect pest homepage to access important information!
Bertha armyworm pheromone trap monitoring update for SK – Cumulative counts arising from weekly data is available here.
Diamondback moth pheromone trap monitoring update for SK – Monitoring has drawn to a close for 2021. Review the final DBM counts. Extremely low numbers have been intercepted. Province-wide, <65 moths have been intercepted (2021Jun28 Carter, pers. comm.). At this point, in-field scouting for larvae remains important.

ALBERTA’S Insect Pest Monitoring Network webpage links to insect survey maps, live feed maps, and insect trap set-up videos and more. There is also a Major Crops Insect webpage. The new webpage does not replace the Insect Pest Monitoring Network page. Remember, AAF’s Agri-News occasionally includes insect-related information or Twitter users can connect to #ABBugChat Wednesdays at 10:00 am.
Wheat midge pheromone trap monitoring update for AB – Cumulative counts arising from weekly data are available so refer to the Live Map.
Cabbage seedpod weevil sweep-net monitoring update for AB – In-field counts can be entered here to populate the Live Map. Some sites in southern Alberta are reporting densities at or above the economic threshold in canola (22Jul2021).
Bertha armyworm pheromone trap monitoring update for AB – Cumulative counts arising from weekly data have begun so refer to the Live Map. Cumulative counts throughout the province report “low risk” numbers of moths so far (22Jul2021).
Diamondback moth pheromone trap monitoring update for AB – Trapping has drawn to a close for 2021. Refer to the Live Map which reports extremely low numbers of moths intercepted so far (<50 province-wide as of 01Jul2021). At this point, in-field scouting for larvae remains important.
Cutworm reporting tool – Refer to the Live Map which now reports seven sites with cutworms (as of 01Jul2021).

Crop report links

Click the provincial name below to link to online crop reports produced by:
Manitoba Agriculture and Resource Development (subscribe to receive OR access a PDF copy of the July 27 2021 report).
Saskatchewan Agriculture (or access a PDF copy of the July 20-26, 2021 report).
Alberta Agriculture and Forestry (or access a PDF copy of the July 13, 2021 report).

The following crop reports are also available:
• The United States Department of Agriculture (USDA) produces a Crop Progress Report (access a PDF copy of the July 26, 2021 edition).
• The USDA’s Weekly Weather and Crop Bulletin (access a PDF copy of the July 27, 2021 edition).

Previous posts

As the growing season progresses, the various Weekly Update topics move on and off the priority list for in-field scouting but they should be kept at hand to support season-long monitoring. Click to review these earlier 2021 Posts (organized alphabetically):
2020-2021 Risk and forecast maps
Alfalfa weevil – predicted development (Wk07)
Aphids in field crops (Wk09)
Bertha armyworm (Wk12)
Bertha armyworm – predicted development (Wk09)
Cabbage seedpod weevil monitoring (Wk09)
Cereal aphid manager APP (Wk07)
Cereal leaf beetle – predicted development (Wk07)
Crop protection guides (Wk03)
Cutworms (Wk02)
Diamondback moth – predicted development (Wk12)
European corn borer – nation-wide monitoring project (Wk07)
Field heroes (Wk08)
Flea beetles (Wk02)
Flea beetles – predicted geographic distribution and abundance (Wk04)
Grasshopper diversity and scouting photos (Wk08)
Grasshopper – predicted development (Wk12)
Ladybird beetles (Wk03)
Lygus bug monitoring (Wk09)
Midges in canola (Wk11)
Monarch migration (Wk09)
Pea leaf weevil (Wk03)
Scouting charts – canola and flax (Wk03)
Slugs and their parasites (Wk04)
Thrips in canola (Wk12)
Weather radar mapping interface (Wk06)
Wheat midge – predicted development (Wk12)
Wind trajectories for monitoring insect movement (Wk02)
Wind trajectories – weekly reports (Wk09)
Wireworms (Wk02)


Wheat stem sawfly (AAFC)

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 the plant is toxic to these insects.

Wheat stem sawfly larvae feed on the pith of plant stems, impacting crop yield and quality. As these 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, at which point nothing can be harvested. Because wheat stem sawflies also breed and develop on native grass species, economic damage is more prevalent around crop margins where these plants crossover.

Wheat stem sawfly larva (AAFC)

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.

Wheat stem sawfly developmental stages (Art Cushman, Bugwood)

Biological and monitoring information related to wheat stem sawflies in field crops can be found on our Monitoring page as well as on provincial Agriculture Ministry pages (Manitoba, SaskatchewanandAlberta). 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).