Weekly Update

Week 15 and swathers and combines are now running across the prairies! Be sure to catch the Insect of the Weekit’s the mormon cricket!

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 past week (August 2-8, 2021) the prairies continued to experience above-average temperatures and extremely dry conditions. The warmest temperatures were observed across southern and central regions of Alberta, Saskatchewan, and Manitoba (Fig. 1). Across the prairies, the average 30-day (July 10 – August 8, 2021) temperature was 2.5°C warmer than climate normal values (Fig. 2). The 2021 growing season (April 1 – August 8, 2021) has been 1.6 °C warmer than average (Fig. 3).

Figure 1. 7-day average temperature (°C) observed across the Canadian prairies for the period of August 2- 8, 2021.
Figure 2. 30-day average temperature (°C) observed across the Canadian prairies for the period of July 10 – August 8, 2021.
Figure 3. Growing season average temperature (°C) observed across the Canadian prairies for the period of April 1 – August 8, 2021.

Growing degree day (GDD) maps for Base 5 ºC and Base 10 ºC (April 1-August 9, 2021) can be viewed by clicking the hyperlinks. Over the past 7 days (August 5-11, 2021), the lowest temperatures recorded across the Canadian prairies ranged from < 0 to >12 °C while the highest temperatures observed ranged from <22 to >34 °C. Check the number of days of >25 °C or >30 °C across the Canadian prairies (April 1-August 11, 2021). Access these maps and more using the AAFC Drought Watch webpage interface.

PRECIPITATION: Weekly (August 2-8, 2021) rainfall amounts were generally less than 5 mm (Fig. 4). Rainfall amounts for the period of July 10 – August 8 (30-day accumulation) have been well below average with most of the prairies receiving less than 40% of the average amount for this time period (Fig. 5). Growing season precipitation has been below average across most of the prairies. A region extending from Regina to the USA border is the only region reporting near-normal rainfall for the period of April 1 – August 8, 2021. A region extending from Lethbridge to northeastern Saskatchewan has had less than 100 mm of rain (Fig. 6) in 2021.

Figure 4. 7-day cumulative rainfall (mm) observed across the Canadian prairies for the period of August 2 – 8, 2021.
Figure 5. 30-day cumulative rainfall (mm) observed across the Canadian prairies for the period of July 10 – August 8, 2021
Figure 6. Growing season cumulative rainfall (mm) observed across the Canadian prairies for the period of April 1 – August 8, 2021.

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.

Lygus bug monitoring

On the Canadian prairies, lygus bugs (Heteroptera: Miridae) are normally a complex of several native species usually including Lygus lineolaris, L. keltoni, L. borealis, L. elisus although several more species are distributed throughout Canada. The species of Lygus forming the “complex” can vary by host plant, by region or even seasonally.

Lygus bugs are polyphagous (i.e., feed on plants belonging to several Families of plants) and multivoltine (i.e., capable of producing multiple generations per year). Both the adult (Fig. 1) and five nymphal instar stages (Fig. 2) are a sucking insect that focuses feeding activities on developing buds, pods and seeds. Adults overwinter in northern climates. The economic threshold for Lygus in canola is applied at late flower and early pod stages.  

Recent research in Alberta has resulted in a revision to the thresholds recommended for the management of Lygus in canola. Under ideal growing conditions (i.e., ample moisture) a threshold of 20-30 lygus per 10 sweeps is recommended. Under dry conditions, a lower threshold may be used, however, because drought limits yield potential in canola, growers should be cautious if considering the use of foliar-applied insecticide at lygus densities below the established threshold of 20-30 per 10 sweeps. In drought-affected fields that still support near-average yield potential, a lower threshold of ~20 lygus per 10 sweeps may be appropriate for stressed canola. Even if the current value of canola remains high (e.g., >$19.00 per bu), control at densities of <10 lygus per 10 sweeps is not likely to be economical. Research indicates that lygus numbers below 10 per 10 sweeps (one per sweep) can on occasion increase yield in good growing conditions – likely through plant compensation for a small amount of feeding stress.

Figure 1. Adult Lygus lineolaris (5-6 mm long) (photo: AAFC-Saskatoon).
Figure 2. Fifth instar lygus bug nymph (3-4 mm long) (photo: AAFC-Saskatoon).

Damage: Lygus bugs have piercing-sucking mouthparts and physically damage the plant by puncturing the tissue and sucking plant juices. The plants also react to the toxic saliva that the insects inject when they feed. Lygus bug infestations can cause alfalfa to have short stem internodes, excessive branching, and small, distorted leaves. In canola, lygus bugs feed on buds and blossoms and cause them to drop. They also puncture seed pods and feed on the developing seeds causing them to turn brown and shrivel.

Scouting tips to keep in mind: Begin monitoring canola when it bolts and continue until seeds within the pods are firm. Since adults can move into canola from alfalfa, check lygus bug numbers in canola when nearby alfalfa crops are cut.

Sample the crop for lygus bugs on a sunny day when the temperature is above 20 °C and the crop canopy is dry. With a standard insect net (38 cm diameter), take ten 180 ° sweeps. Count the number of lygus bugs in the net. Sampling becomes more representative IF repeated at multiple spots within a field so sweep in at least 10 locations within a field to estimate the density of lygus bugs.

How to tell them apart: The 2019 Insect of the Week’s doppelganger for Wk 15 was lygus bug versus the alfalfa plant bug while Wk 16 featured lygus bug nymphs vs. aphids!  Both posts include tips to discern the difference between when doing in-field scouting!

Biological and monitoring information related to Lygus in field crops is posted by the provinces of Manitoba or Alberta fact sheets or the Prairie Pest Monitoring Network’s monitoring protocol.  Also refer to the Lygus pages within the new “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” – both English or French versions are available.

Predicted diamondback moth development

Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. The model, based on climate data, indicates most DBM populations should be in the third generation (Fig. 1). Model simulations to August 8, 2021, predict an additional generation for the current growing season PLUS a third and fourth generation of non-migrant adults are currently emerging across the Canadian prairies (Fig. 2).

Figure 1. Predicted number of non-migrant generations of diamondback moth (Plutella xylostella) expected to occur across the Canadian prairies as of August 8 (based on climate normals data).
Figure 2. Predicted number of non-migrant generations of diamondback moth (Plutella xylostella) expected to occur across the Canadian prairies as of August 8, 2021.

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. 3) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.

Figure 3. 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  (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).

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Figure 4. Diamondback moth pupa within silken cocoon.
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Figure 5. Diamondback moth.

Biological and monitoring information for DBM (including tips for scouting and economic thresholds) is posted by Manitoba Agriculture and Resource DevelopmentSaskatchewan Agriculture, and the Prairie Pest Monitoring Network.  Also, refer to the diamondback moth pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (accessible in either English-enhanced or French-enhanced versions).

Predicted grasshopper development

Model simulations were used to estimate grasshopper (Melanoplus sanguinipes) development as of August 8, 2021. Compared to average growing season temperatures, above-average temperatures during June, July, and early August continue to result in a noticeable increase in the rate of grasshopper development.

Oviposition generally begins in early August. Model simulations for 2021 predicted that oviposition was expected to begin in mid-July. Earlier oviposition can result in above-average production of eggs resulting in potential risk for the following growing season. Climate data suggests that, as of August 8, oviposition would be expected to occur across most of the southern prairies (Fig. 1). Model runs for the 2021 growing season (April 1 – August 8) predicted that oviposition should now be occurring across most of the prairies (Fig. 2).

Figure 1. Percent of grasshopper (Melanoplus sanguinipes) population in the egg stage across the Canadian prairies as of August 8 (based on climate normals data).
Figure 2. Percent of grasshopper (Melanoplus sanguinipes) population in the egg stage across the Canadian prairies as of August 8, 2021.

Grasshopper Scouting Steps:
Review grasshopper diversity and scouting information including photos of nymphs, adults, and non-grasshopper species to aid in-field scouting and accurately apply thresholds for grasshoppers.
● Measure off a distance of 50 m on the level road surface and mark both starting and finishing points using markers or specific posts on the field margin.
● Start at one end in either the field or the roadside and walk toward the other end of the 50 m, making some disturbance with your feet to encourage any grasshoppers to jump.
● Grasshoppers that jump/fly through the field of view within a one-meter width in front of the observer are counted.
● A meter stick can be carried as a visual tool to give perspective for a one-meter width. However, after a few stops, one can often visualize the necessary width and a meter stick may not be required. Also, a hand-held counter can be useful in counting while the observer counts off the required distance.
● At the endpoint, the total number of grasshoppers is divided by 50 to give an average per meter. For 100 m, repeat this procedure.
Compare counts to the following damage levels associated with pest species of grasshoppers:
0-2 per m² – None to very light damage
2-4 per m² – Very light damage
4-8 per m² – Light damage
8-12 per m² – Action threshold in cereals and canola
12-24 per m² – Severe damage
24 per m² – Very severe damage
For lentils at flowering and pod stages, >2 per m² will cause yield loss.
For flax at boll stages, >2 per m² will cause yield loss.
● More practically, the following thresholds are offered but, in the event of additional crop stress (e.g., drought), the use of “may be required” versus “control usually required” requires careful consideration:

Biological and monitoring information (including tips for scouting and economic thresholds) related to grasshoppers in field crops is posted by Manitoba Agriculture and Resource DevelopmentSaskatchewan AgricultureAlberta Agriculture and Forestry, the BC Ministry of Agriculture, and the Prairie Pest Monitoring Network.  Also, refer to the grasshopper pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (accessible in either English-enhanced or French-enhanced versions).

Predicted wheat midge development

Wheat midge model simulations to August 8, 2021, predict that wheat midge populations should be in one of two larval stages. Where wheat midge is present, most larvae (55 %) will be in wheat heads, feeding on developing kernels. Development of this stage is predicted to be greatest across eastern Saskatchewan. Larvae that have completed development in wheat heads will be dropping to the soil where they will transition to larval cocoons (44 % of the prairie population). The occurrence of larval cocoons should be greatest across northwestern Saskatchewan and eastern Alberta. This stage will overwinter in the soil.

Figure 1. Percent of the wheat midge (Sitodiplosis mosellana) larval population that is predicted to be in wheat heads as of August 8, 2021.
Figure 2. Percent of the wheat midge (Sitodiplosis mosellana) larval population that is predicted to be in the soil (larval cocoons) as of August 8, 2021.

Monitoring: The window for scouting and application of the economic threshold for wheat midge (i.e., during the synchrony between wheat anthesis and midge flight period) has now drawn to a close for 2021. 

Wheat midge was featured as the Insect of the Week in 2021 (for Wk07). Be sure to also review wheat midge and its doppelganger, the lauxanid fly, featured as the Insect of the Week in 2019 (for Wk11) – find descriptions and photos to help with in-field scouting!  Additionally, the differences between midges and parasitoid wasps were featured as the Insect of the Week in 2019 (for Wk12).  Remember – not all flying insects are mosquitoes nor are they pests! Many are important parasitoid wasps that actually regulate insect pest species in our field crops OR pollinators that perform valuable ecosystem services!

Information related to wheat midge biology and monitoring can be accessed by linking to your provincial fact sheet (Saskatchewan Agriculture or Alberta Agriculture & Forestry).  A review of wheat midge on the Canadian prairies was published by Elliott, Olfert, and Hartley in 2011.  

Alberta Agriculture and Forestry has a YouTube video describing in-field monitoring for wheat midge.  

More information about wheat midge can be found by accessing the pages from the new “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide”.  View ONLY the Wheat midge pages but remember the guide is available as a free downloadable document as both an English-enhanced or French-enhanced version.

Crop Metrics Application

Agriculture and Agri-Food Canada has released the Canadian Crop Metrics application. This product contains useful and interesting information about the current status of crops grown across Canada. The application also presents data for a number of pest insects including bertha armyworm, diamondback moth, grasshoppers and wheat midge.

Read over the synopsis of the Canadian Crop Metrics application to gain a sense of what the resource has to offer and how to optimize access. It allows users to look at specific regions and generate reports, graphs, and tables to compare current conditions to historical conditions for 11 different crop types. Weather data is updated regularly and yield estimates are updated monthly from July to October. Forecasts are made at the beginning of the months of July, August and September for all crops, and an additional forecast is made for corn and soybeans (late season crops) at the beginning of October. Forecasts are jointly produced by Agriculture and Agri-Food Canada and Statistics Canada using historical yield, climate and satellite data as inputs.

Screenshots of the application are below for reference. Get started here!

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 August 8, 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 of >400 degree-days 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 August 8) should also start to use DEET this week!

Figure 1. Predicted development of Culex tarsalis across the Canadian prairies (as of August 1, 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 August12, 2021). The screenshot below (retrieved 12Aug2021) 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 12Aug2021).

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.

Field heroes

The Field Heroes campaign continues to raise awareness of the role of beneficial insects in western Canadian crops.

Two NEW Field Heroes resources for 2021 include:

  1. Real Agriculture went live in 2021 with Season 2 of the Pest and Predators podcast series!
    • NEW – Episode 12 – Get a jump on grasshoppers (July 6, 2021; S. Haney and J. Tansey)
    • Episode 11 – Free farm labour (June 15, 2021; S. Haney and J. Gavloski)
    • Episode 10 – Good bugs relocate for work (June 1, 2021; S. Haney and H. Carcamo)
    • Episode 9 – Secret agents in the stubble (May 18, 2021; S. Haney and J. Otani)
    • Episode 8 – Good vs pea leaf weEVIL (May 4, 2021; S. Haney and M. Vankosky)
    • Episode 7 – Powerful parasitoids: Better than fiction (April 20, 2021; S. Haney and T. Wist)
    • Review SEASON 1 of the Pest and Predators podcast series!
  2. The NEW Pests and Predators Field Guide is filled with helpful images for quick insect identification and plenty of tips to manage the pests AND natural enemies in your fields. Claim your free copy at http://fieldheroes.ca/fieldguide/ or download a free copy to arm your in-field scouting efforts!

Access ALL the Field Heroes links here and be sure to follow @FieldHeroes!

Pre-Harvest Intervals (PHI)

Reminder – 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.

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 August 11, 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!

SASKATCHEWAN’S Crop Production News is available. Access Issue #5 online which includes information describing supporting pollinators in an agriculture habitat. Be sure to bookmark their insect pest homepage to access important information!

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.

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 August 10, 2021 report; retrieved 12Aug2021).
Saskatchewan Agriculture (or access a PDF copy of the August 3-9, 2021 report; retrieved 12Aug2021).
Alberta Agriculture and Forestry (or access a PDF copy of the July 27, 2021 report; retrieved 12Aug2021).

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 August 9, 2021 edition; retrieved 12Aug2021).
• The USDA’s Weekly Weather and Crop Bulletin (access a PDF copy of the August 10, 2021 edition; retrieved 12Aug2021).

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)
Calls for survey help (Wk14)
Cereal aphid manager APP (Wk07)
Cereal leaf beetle – predicted development (Wk07)
Crop protection guides (Wk03)
Cutworms (Wk02)
European corn borer – nation-wide monitoring project (Wk07)
Flea beetles (Wk02)
Flea beetles – predicted geographic distribution and abundance (Wk04)
Fuzzy white “eggs” on barley or wheat (Wk13)
Grasshopper diversity and scouting photos (Wk08)
Ladybird beetles (Wk03)
Midges in canola (Wk11)
Monarch migration (Wk09)
Pea leaf weevil (Wk03)
Praire-wide survey of stored grain pests (Wk13)
Scouting charts – canola and flax (Wk03)
Slugs and their parasites (Wk04)
Thrips in canola (Wk12)
Weather radar mapping interface (Wk06)
Wind trajectories for monitoring insect movement (Wk02)
Wind trajectories – weekly reports (Wk09)
Wireworms (Wk02)


Mormon cricket (Bugwood)

With a common name that cites the devastation these insects brought upon crops during an 1848 outbreak in the Great Salt Lake Basin, Mormon crickets have equal potential to do damage on the Canadian Prairies. Like other grasshopper species, mormon crickets will consume various crops, including wheat, barley, alfalfa and sweet clover, in addition to other forages and garden vegetables. These crickets will also eat other insects, including smaller mormon crickets.

Droughts drive mormon cricket outbreaks, at which time these insects will have a greater economic impact on crops. Migrating swarms will consume all parts of their plant host, ravaging crops and reducing their marketable yields. In addition to this, baled alfalfa containing crickets is unpalatable to livestock, reducing its viability as a feed source.

Adults are 40-50 mm long with stout bodies. Their colour depends on how dense the population is: swarming mormon crickets can be black, brown, or red, and individual insects can be purple or green. Both the abdomen and the “shield” (pronotum) behind the crickets’ head may be striped. The females’ have a long egg-laying organ (ovipositor) and both sexes have antennae longer than their bodies. Mature nymphs resemble adults in colour and appearance but are somewhat smaller and females lack an ovipositor.

Biological and monitoring information related to mormon crickets in field crops can be found on our Monitoring page. For more information, visit the mormon cricket 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).