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.
TEMPERATURE: Though temperatures over the past 30 days have been warmer than normal, the 2022 growing season across the prairies has been quite similar to that of a ‘normal’ or long-term average season. This past week (July 18-24, 2022), the average daily temperature on the prairies was 2 °C cooler than the average daily temperature of the previous week and 1 °C warmer than the long-term normal temperature. The coolest temperatures were observed across central and northern Alberta (Fig. 1).
Figure 1. Seven-day average temperature (°C) across the Canadian prairies for the period of July 18-24, 2022.
The prairie-wide average 30-day temperature (June 25 – July 24, 2022) was 0.5 °C warmer than the long-term average value. Average temperatures have been warmest across the southern prairies (Fig. 2).
Figure 2. 30-day average temperature (°C) across the Canadian prairies for the period of June 25-July 24, 2022.
The average growing season (April 1-July 24, 2022) temperature for the prairies has been 0.2 °C cooler than the climate normal values. The growing season has been warmest across the southern prairies (Fig. 3).
Figure 3. Growing season average temperature (°C) observed across the Canadian prairies for the period of April 1 to July 24, 2022.
PRECIPITATION: Weekly rainfall accumulation for July 18 to 24 varied across the prairies. Very little precipitation has fallen across the northern prairies (Fig. 4). Observed rainfall amounts across central and northern Alberta were generally less than 5 mm. 30-day (June 25 – July 24, 2022) rainfall amounts have been well below average for the northern prairies and near normal across the southern prairies (Fig. 5).
Figure 4 Seven-day cumulative rainfall (mm) observed across the Canadian prairies for the period of July 18-24, 2022.Figure 5. 30-day cumulative rainfall (mm) observed across the Canadian prairies the past 30 days (June 25-July 24, 2022).
Growing season rainfall for April 1 – July 24, 2022, continues to be greatest across Manitoba and eastern Saskatchewan; cumulative rainfall amounts have been much lower for the central and western regions of Saskatchewan and Alberta (Fig. 6).
Figure 6. Growing season cumulative rainfall (mm) observed across the Canadian prairies for the period of April 1 to July 24, 2022.
The grasshopper (Acrididae: Melanoplus sanguinipes) model predicts development using biological parameters known for the pest species and environmental data observed across the Canadian prairies on a daily basis. Model outputs provided below as geospatial maps are a tool to help time in-field scouting on a regional scale yet local development can vary and is only accurately assessed through in-field scouting.
Some areas of the Canadian prairies are presently experiencing high densities of economically important species. Review lifecycle and damage information for this pest to support in-field scouting.
Model simulations were used to estimate grasshopper development as of July 24, 2022. As a result of above-normal temperatures, grasshopper development has rapidly progressed over the past few weeks. Last week, adults were just beginning to appear. Based on estimates of average development, populations should consist of 4th (25%) and 5th (34%) instar nymphs and adults (19%) across the southern regions of all three prairie provinces (Fig. 1). Adults should now be occurring across the southern regions of all three prairie provinces (Fig. 2). Potential risk continues to be greatest across the central and southern regions of Saskatchewan.
Figure 1. Predicted migratory grasshopper (Melanoplus sanguinipes) development, presented as average instar, across the Canadian prairies as of July 24, 2022.Figure 2. Long-term average predicted migratory grasshopper (Melanoplus sanguinipes) development, presented as the percent adults, across the Canadian prairies as of July 17, 2022.
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.
Model simulations to July 24, 2022, indicate that the third generation of non-migrant adults (based on mid-May arrival dates) are currently occurring across the southern prairies (Fig. 1). DBM development is predicted to be marginally greater than long-term average values (Fig. 2).
Figure 1. Predicted number of non-migrant generations of diamondback moth (Plutella xylostella) expected to have occurred across the Canadian prairies as of July 24, 2022. Figure 2. Long-term predicted number of non-migrant generations of diamondback moth (Plutella xylostella) expected to have occurred across the Canadian prairies as of July 24, based on climate normal data.
Spring Pheromone Trap Monitoring of Adult Males: Across the Canadian prairies, spring monitoring is initiated to acquire weekly counts of adult moths attracted to pheromone-baited delta traps deployed in fields. Weekly trap interceptions are observed to generate cumulative counts. Summaries or maps of cumulative DBM data are available for Manitoba, Saskatchewan and Alberta. These cumulative count estimates are broadly categorized to help producers prioritize and time in-field scouting for larvae.
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.
The following maps represent predicted regional estimates of wheat midge development. Remember – field level populations are assessed only through in-field scouting.
As of July 24, 2022, where wheat midge is present, model simulations predict that Albertan populations should be primarily in the egg stage, while populations across Manitoba and eastern Saskatchewan should consist of larvae developing in wheat heads (Fig. 1).
Figure 1. Wheat midge larvae (AAFC)
Regional differences in wheat midge development can be attributed to rainfall differences that occurred in May and June. Optimal rainfall in May and June across Saskatchewan and Manitoba has resulted in faster rates of wheat midge development rates than in Alberta. As a result, some adult wheat midge may still be active in Alberta (Fig. 2), while adult populations should have peaked and should be declining across Saskatchewan and Manitoba. Populations in the Peace River region are predicted to be primarily in the egg stage (Fig. 3). Across Manitoba and Saskatchewan, populations are predicted to be transitioning from the egg stage to the larval stage (Fig. 4). Wheat midge developmental rates near Regina, Saskatchewan are predicted to be greater than for Grande Prairie, Alberta.
Figure 2. Percent of wheat midge larval population (Sitodiplosis mosellana) that is in the adult stage, across western Canada,as of July 24, 2022.Figure. 3. Percent of wheat midge population (Sitodiplosis mosellana) that is in the egg stage across western Canada, as of July 24, 2022.Figure 4. Percent of wheat midge population (Sitodiplosis mosellana) that is in the larval stage (in wheat heads), across western Canada, as of July 24, 2022.
Model simulations indicate that egg development is complete and populations are primarily in the larval stage (>90%) for populations near Regina (Fig. 5) while Grande Prairie populations are predicted be in both egg (31%) and larval stages (61%) (Fig. 6). Potential risk continues to be greatest across eastern Saskatchewan and Manitoba.
Figure 5. Predicted development of wheat midge (Sitodiplosis mosellana) and wheat development near Regina, Saskatchewanas of July 24, 2022. Figure 6. Predicted development of wheat midge (Sitodiplosis mosellana) and wheat development near Grande Prairie, Alberta,as of July 24, 2022.
In-Field 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 2022.
Additional information can be accessed by reviewing the Wheat midge pages extracted from the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.
Aphid populations can quickly increase at this point in the season and particularly when growing conditions are warm and dry. Over the years, both the Weekly Updates and Insect of the Week included aphid-related information so here’s a list of these items to access when scouting fields:
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.
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 “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. The Canola Council of Canada’s “Canola Encyclopedia” also summarizes Lygus bugs. The Flax Council of Canada includes Lygus bugs in their Insect Pest downloadable PDF chapter plus the Saskatchewan Pulse Growers summarize Lygus bugs in faba beans.
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 (e.g., lower left photo). Mating and oviposition are quickly followed by eggs hatching within developing canola pods (e.g., lower right photo). The highly concealed larvae feed within the pod, consuming the developing seeds.
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 (refer to lower 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 (refer to lower 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, feeding on the developing seeds. A single larva consumes about 5 canola seeds. The mature larva chews a small, circular exit hole 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.
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 and check the live map for CSPW posted by Alberta Agriculture and Forestry (screenshot provided below for reference; retrieved 2022Jul28).
The pea leaf weevil is a slender greyish-brown insect measuring approximately 5 mm in length (Fig. 1, Left image). Pea leaf weevil resembles the sweet clover weevil (Sitona cylindricollis) but the former is distinguished by three light-coloured stripes extending length-wise down thorax and sometimes the abdomen. All species of Sitona, including the pea leaf weevil, have a short snout.
Figure 1. Comparison images and descriptions of four Sitona species adults including pea leaf weevil (AAFC-Otani).
Adults will feed upon the leaf margins and growing points of legume seedlings (alfalfa, clover, dry beans, faba beans, peas) and produce a characteristic, scalloped (notched) edge (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. 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.
Larvae develop under the soil and are “C” shaped and milky-white with a dark-brown head capsule ranging in length from 3.5-5.5 mm (Figure 3). Larvae develop through five instar stages. After hatching, larvae seek and enter the roots of a pea plant. Larvae will enter and consume the contents of the nodules of the legume host plant. It is the nodules that are responsible for nitrogen-fixation which affect yield plus the plant’s ability to input nitrogen into the soil. Consumption of or damage to the nodules (Figure 4) results in partial or complete inhibition of nitrogen fixation by the plant and results in poor plant growth and low seed yields.
Figure 3. Larva of pea leaf weevil in soil (Photo: L. Dosdall).Figure 4. Damaged pea nodules (Photo: L. Dosdall).
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 24, 2022, C. tarsalis development is now on the verge of the second generation of adults beginning to fly in areas highlighted yellow (i.e., 250-300 DD of base 14.3 °C) represented below in Figure 1. Outdoor enthusiasts falling within areas highlighted orange or yellow should begin to wear DEET to protect against WNV! Historically, southern and central regions of the Canadian prairies are now in a period of increased risk for WNV that typically peaks over the long weekend in August.
Figure 1. Predicted development of Culex tarsalis across the Canadian prairies (as of July 24, 2022).
For those following the specifics of the mosquito host-WNV interaction, Figure 2 projects how many days it will take a C. tarsalis female to become fully infective and be able to transmit the virus to another host (bird or human) once the virus is acquired from another bird. This represents the extrinsic incubation period (EIP) of the virus within the mosquito. Figure 2 projects the EIP is approximately 17 days in areas highlighted red and approximately 15 days in areas highlighted pink.
Figure 2. Predicted extrinsic incubation period (EIP) of West Nile Virus within a C. tarsalis female as of July 24, 2022.
The above maps should be compared with historical confirmed cases of WNV. 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 November 18, 2021; retrieved July 28, 2022). The screenshot below (retrieved 28Jul2022) serves as a background reference of what was reported in 2021.
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 28Jul2022).
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.
Prompted by recent discussions at Results Driven Agriculture Research (RDAR) meetings, a survey has been initiated as part of an M.Sc. research project in the Faculty of Science at the University of Alberta to assess the effectiveness and producer preferences for entomological extension in agriculture in Alberta. The project is funded by RDAR and the Alberta Pulse Growers.
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 Keep 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. • Access the Pre-Harvest Glyphosate Stage Guide. • And remember Provincial crop protection guides include the PHI for every pesticide x crop combination. The 2022 Crop Production Guides are available as a FREE downloadable PDF for Alberta, Saskatchewan, and Manitoba.
