TEMPERATURE: Average temperatures for the 2022 growing season continue to be similar to long-term average values. This past week (August 8-14, 2022), the average daily temperature for the prairies was 2 °C warmer than the previous week and 2.5 °C warmer than climate normals. The warmest temperatures were observed across southwestern Saskatchewan and the southern and central regions of Alberta (Fig. 1). The prairie-wide average 30-day temperature (July 16 – August 14, 2022) was 1.5 °C warmer than the long-term average 30-day temperature. Average temperatures have been warmest across southern Alberta and southwestern Saskatchewan (Fig. 2).
The average growing season (April 1-August 14, 2022) temperature for the prairies has been similar to observed climate normal values. The growing season has been coolest across the Peace River region (Fig. 3).
PRECIPITATION: The greatest weekly precipitation amounts occurred across eastern Saskatchewan last week (August 8-14, 2022) (Fig. 4). 30-day (July 16-August 14, 2022) rainfall amounts continue to be greatest across southeastern Manitoba while dry conditions persist across southern Alberta and southwestern Saskatchewan (Fig. 5).
Growing season rainfall for the prairies (April 1 – August 14, 2022) has been near normal for Alberta and above normal in Manitoba. Total rainfall continues to be greatest across Manitoba and eastern Saskatchewan and least across central and south-central Saskatchewan (Fig. 6).
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.
Model simulations were used to estimate grasshopper development as of August 14, 2022. Potential risk continues to be greatest across central and southern regions of Saskatchewan and southeastern Alberta. Simulations indicate that prairie populations are in the adult stage and females are beginning to lay eggs in the soil. Earlier oviposition can result in above-average production of eggs and increased overwintering survival of eggs.
The oviposition index provides a method to assess where egg production is greatest; higher oviposition index values indicate where egg production is greatest. Model runs for the 2022 growing season (April 1 – August 14) predicted that ovipositon rates so far in 2022 have been greatest across southern Saskatchewan and southeastern Alberta (Fig. 1).
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.
Recent warm conditions have resulted in the rapid development of diamondback moth populations. Model simulations to August 14, 2022, indicate that the fourth 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 in 2022 than expected based on long-term average values (Fig. 2).
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.
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).
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.
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 continues 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.
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.
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 14, 2022and where present, C. tarsalis development has progressed. Remember, areas highlighted yellow have accumulated sufficient heat units for the second generation of C. tarsalis to fly. Many areas of the prairies well exceed the 250-300 DD of base 14.3 °C (e.g., areas orange red any any shade of pink) represented in Figure 1. Outdoor enthusiasts falling within areas highlighted yellow, orange, red or pink should wear DEET to protect against WNV! Historically, southern and central regions of the Canadian prairies are at increased risk for WNV from late July but typically peaks over the long weekend in August.
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 was approximately 12-15 days in areas highlighted mauve and approximately 22-24 days in areas highlighted light green.
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 July 30, 2022; retrieved August 18, 2022) and provided below.
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.