Ross Weiss, Tamara Rounce, David Giffen, Owen Olfert, Jennifer Otani and Meghan Vankosky
TEMPERATURE: Average temperatures for the 2022 growing season have been similar to long-term average temperature values. This past week (July 25-31, 2022), the average daily temperature on the prairies was 1 °C cooler than the average daily temperature of the previous week and 1.5 °C warmer than the long-term normal temperature. The coolest temperatures were observed across Manitoba and eastern Saskatchewan (Fig. 1).
The prairie-wide average 30-day temperature (July 2 – July 31, 2022) was 1.5 °C warmer than the long-term average value. Average temperatures have been warmest across a region that extends south from Lethbridge to Saskatoon to Winnipeg (Fig. 2).
The average growing season (April 1-July 31, 2022) temperature for the prairies has been similar to climate normal values. The growing season has been coolest across the Parkland and Peace River regions (Fig. 3).
PRECIPITATION: Last week (July 25 to 31), southern Alberta and southwestern Saskatchewan received the lowest amounts of rain of locations across the prairies (Fig. 4). Over the last 30 days (July 2 – July 31, 2022), rainfall amounts have been well below average for northern Alberta and near normal across the central and southern regions of Alberta and Saskatchewan (Fig. 5).
Precipitation has been above normal in Manitoba. The average growing season rainfall for the prairies (April 1 – July 31, 2022) has been approximately 150% of normal. Total rainfall 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. Cumulative rainfall amounts have been near normal for the remainder of Saskatchewan and in Alberta (Fig. 6).
Ross Weiss, Tamara Rounce, David Giffen, Jennifer Otani, Owen Olfert and Meghan Vankosky
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 31, 2022. Grasshopper development has progressed rapidly over the past few weeks and development rates are more advanced this year than expected based on long-term climate normal values. Based on estimates of average development, populations should consist of 4th (18%) and 5th (37%) instar nymphs and adults (33%) 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. 1). Model output indicates that oviposition (egg-laying) is now occurring across the southern prairies (Fig. 2). Potential risk continues to be greatest across the central and southern regions of Saskatchewan.
Ross Weiss, Tamara Rounce, David Giffen, Owen Olfert, Jennifer Otani, John Gavloski, James Tansey, Carter Peru, Shelley Barkley and Meghan Vankosky
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 31, 2022, indicate that the third generation of non-migrant adults (based on mid-May arrival dates) is currently occurring across the southern prairies (Fig. 1). DBM development is predicted to be marginally greater this year 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. 3) 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 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.
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:
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.
Provincial entomologists provide insect pest updates throughout the growing season so link to their information:
MANITOBA’SCrop Pest Updates for 2022 are up and running! Access the August 3 issue as a PDF on their website. Bookmark their Crop Pest Update Index to readily access these reports and also bookmark their insect pest homepage to access fact sheets and more! • Pests of greatest concern in Manitoba from July 28 to August 3 were armyworms, aphids and grasshoppers. The August 3 update has great information on scouting and monitoring for these pests!
With the 2022 growing season well underway, we decided to feature an insect that is becoming a growing problem on the Canadian Prairies: Spotted Wing Drosophila (SWD), Drosophila suzukii.
This invasive insect is thought to have originated in southeast Asia. The first record of SWD is from Japan in 1916. SWD is now established in small and stone fruit production areas throughout North America. SWD has been reported in British Columbia since 2009, and was first reported in Alberta in 2010. Occurrence in Alberta, and low levels in southern Manitoba in 2019 suggested that SK infestations were likely imminent. Monitoring for this pest conducted by the Saskatchewan Ministry of Agriculture began in 2019. Populations were detected throughout the province that year, spurring continued monitoring. Data from 2021 and 2022 indicate continued widespread distribution throughout the province. Early season detection of significant numbers suggests overwintering populations on the prairies.
SWD is an economic pest of many soft fruits, including raspberries, strawberries, cherries, blueberries and plums. Saskatoon berry has been documented as a host. Haskap is also considered to be susceptible but may escape major damage, as SWD populations typically do not increase until after harvest. However, Ontario haskap growers have seen economic losses when a mild winter is coupled with factors that lead to delayed ripening. SWD adults are 3-4 mm, yellow-brown with red eyes. Males have a conspicuous spot on the leading edge of each wing (Figure 1).
Females lack the spots but have a characteristic large, serrated ovipositor (Figure 2).
SWD overwinter as adults. These become active in the spring, mate and seek egg-laying sites. Female SWD lay as many as 16 eggs per day for up to two months. An average of 384 eggs are produced by each female. With their serrated ovipositor, female SWD deposit eggs under the skin of healthy, ripening fruit. Oviposition sites look like pin-holes in the skin (Figure 3). These can also serve as avenues of entry to pathogens like brown rot and botrytis.
Several larvae can occur per fruit (Figure 4). Larval feeding causes fruit to become prematurely soft and unmarketable. Larvae mature in 3-13 days and pupate most commonly in the fruit. The pupal stage lasts another 3-15 days. Multiple generations per year are common.
Although SWD adults can be moved around by winds, movement of contaminated plant material is the major route for initial dispersal. Current management includes culling and destruction of soft fruit and the application of insecticides to limit populations. There are several products registered to control SWD. These can be found here: http://pr-rp.hc-sc.gc.ca/ls-re/index-eng.php. Use the search term ‘spotted wing drosophila’. Product updates occur periodically so check this site regularly.