This past week (July 28 to August 3, 2020) prairie temperatures were warmest in southeastern Alberta and southwestern Saskatchewan and coolest in southern Manitoba and the Peace River region of Alberta and British Columbia (Fig. 1). Temperatures in the past week represent a switch from previous weeks, where it was warmer in Manitoba than in Alberta. Average 30-day temperatures (July 5 to August 3, 2020) continue to be cooler across most of Alberta than observed in eastern Saskatchewan and Manitoba (Fig. 2). The average 30-day temperature at Winnipeg and Brandon continued to be greater than locations in Alberta and Saskatchewan (Fig. 2).
Cumulative rainfall for the past 7 days was lowest across southern regions of Alberta, Saskatchewan and Manitoba (Fig. 4). Cumulative 30-day rainfall was lowest across a large area ranging from southwest Saskatchewan to Saskatoon (Fig. 5). Growing season rainfall (percent of average) is below normal across eastern Saskatchewan and localized areas of Manitoba and above normal across most of Alberta (Fig. 6).
The growing degree day map (GDD) (Base 5 ºC, April 1-August 3, 2020) is below (Fig. 7) while the growing degree day map (GDD) (Base 10 ºC, April 1-August 3, 2020) is shown in Figure 8.
The highest temperatures (°C) observed across the Canadian prairies the past seven days ranged from <24 to >32 °C (Fig. 9). So far this growing season (as of August 6, 2020), the number of days above 25°C ranges from 0-10 days throughout much of Alberta and into the BC Peace then extends up to 51-60 days in southern Manitoba (Fig. 10).
Model simulations for August 3, 2020, indicate that BAW development varies across the prairies. Figures 1 and 2 demonstrate that BAW populations near Winnipeg (Fig. 1) are more advanced than populations near Grande Prairie (Fig. 2). Populations near Winnipeg are predicted to be developing to pupae (Fig. 1). BAW populations near Grande Prairie are expected to be primarily in the larval stage (Fig. 2).
Weekly Pheromone-baited Trapping Results – Early season detection of bertha armyworm is improved through the use of pheromone-baited unitraps traps deployed in fields across the Canadian prairies. Click each province name to access moth reporting numbers observed in Alberta, Saskatchewan and Manitoba(as they become available). Check these sites to assess cumulative counts and relative risk in your geographic region but remember in-field scouting is required to apply the economic threshold to manage both this pest and its natural enemies. For convenience, screen shots of the above maps or data have been placed below for Alberta, Saskatchewan, and Manitoba.
Larval sampling should commence once the adult moths are noted.
Sample at least three locations, a minimum of 50 m apart.
At each location, mark an area of 1 m2 and beat the plants growing within that area to dislodge the larvae.
Count them and compare the average against the values in the economic threshold table below:
Scouting tips: ● Some bertha armyworm larvae remain green or pale brown throughout their larval life. ● Large larvae may drop off the plants and curl up when disturbed, a defensive behavior typical of cutworms and armyworms. ● Young larvae chew irregular holes in leaves, but normally cause little damage. The fifth and sixth instar stages cause the most damage by defoliation and seed pod consumption. Crop losses due to pod feeding will be most severe if there are few leaves. ● Larvae eat the outer green layer of the stems and pods exposing the white tissue. ● At maturity, in late summer or early fall, larvae burrow into the ground and form pupae.
Based on Harcourt (1954) the DBM model was run with a biofix of May 15, 2020. Model runs (as of August 3, 2020) were conducted with weather data for 2020 (Fig. 1) and climate normals (long term average temperatures). The first map illustrates that potentially three generations have been completed across Manitoba and southeastern Saskatchewan (Fig. 1). Most of the prairies have had two generations (Fig. 1). The second map, showing results for climate normal data, indicates that prairie populations should have completed two generations (Fig. 2).
The charts provide location specific details regarding potential development at Winnipeg (Fig. 3) and Lacombe (Fig. 4). The first chart illustrates DBM development at Winnipeg. Results indicate that there is potential for a fourth generation of DBM to occur in southern Manitoba. Populations near Lacombe are predicted to be completing the second generation.
Remove the plants in an area measuring 0.1 m² (about 12″ square). Beat them on to a clean surface and count the number of larvae (Fig. 5) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
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).
As of August 3, 2020, the grasshopper model estimates that prairie grasshopper populations are primarily adults (Fig. 1). Based on model simulations, development has been slowest across central and northern regions of Alberta (Fig. 1). The second map provides an overview of where oviposition is predicted to have started (Fig. 2). The yellow and red areas show that oviposition has begun across southern Manitoba and southeastern Saskatchewan (Fig. 2).
The two graphs compare grasshopper development at Saskatoon (Fig. 3) and Brandon (Fig. 4). Near Saskatoon, grasshopper populations are expected to be mainly in the adult stage with oviposition beginning to occur over the past week (Fig. 3). Around Brandon, adult emergence is complete and oviposition should be well underway (Fig. 4).
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. Adults overwinter in northern climates. The economic threshold for Lygus in canola is applied at late flower and early pod stages.
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. In fact, sampling is most accurate when repeated at a total of 15 spots within the field. Samples can be taken along or near the field margins. Calculate the cumulative total number of lygus bugs and then consult the sequential sampling chart (Figure 3).
If the total number is below the lower threshold line (Fig. 3), no treatment is needed. If the total is below the upper threshold line, take more samples. If the total is on or above the upper threshold line, calculate the average number of lygus bugs per 10-sweep sample and consult the economic threshold tables (Tables 1 and 2).
The economic threshold for lygus bugs in canola covers the end of the flowering (Table 1) and the early pod ripening stages (Table 2). Once the seeds have ripened to yellow or brown, the cost of controlling lygus bugs may exceed the damage they will cause prior to harvest, so insecticide application is not warranted. Consider the estimated cost of spraying and expected return prior to making a decision to treat a crop.
Remember that insecticide applications at bud stage in canola have not been proven to result in an economic benefit in production. The exception to this is in the Peace River region where early, dry springs and unusually high densities of lygus bug adults can occasionally occur at bud stage. In this situation, high numbers of lygus bugs feeding on moisture-stressed canola at bud stage is suspected to result in delay of flowering so producers in that region must monitor in fields that fail to flower as expected.
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.
Thrips in canola (Thynsanoptera) – While scouting at this time of year, curled canola pods may be encountered. The culprits are quite possibly thrips.
Damage: Flower thrips (Thysanoptera) are pests of a broad range of plants including cereals and broadleaved crops such as canola. Thrips are minute, slender-bodied insects with rasping-sucking mouthparts and feed by rasping the surface of canola buds and sucking up plant fluids.
Biology: Thrips have six life stages: egg, two larval stages, a prepupal and pupal stage and an adult. Both adults and nymphs cause damage by feeding on the flower and buds. Limited surveys in 1999 in Saskatchewan and Alberta indicated that the predominant species were Frankliniella tritici (flower thrip) followed by Thrips tabaci (onion thrip) and T. vulgatissimus (no common name).
In canola, pods damaged by thrips are often curled and tend to drop prematurely. Some species, such as T. vulgatissimus have been credited with contributing to pollination.
Ladybird beetle larvae (Fig. 1), pupae (Fig. 2), and adults (Fig. 3) can all be found in fields at this time of year. Take a look at the various stages and the many patterns of native and introduced species to recognize these as Field Heroes! Ladybird beetles are categorized as general predators and will feed on several species of arthropods but are partial to aphids.
Provincial entomologists provide insect pest updates throughout the growing season so link to their information:
• Manitoba‘s Crop Pest Updates for 2020 are available. Access the August 5, 2020 report. The summary indicates that, “Grasshoppers are currently the biggest insect concern. Some sunflower midge has been observed in sunflowers in the Eastern region, mainly around field edges, which is typical for this insect. Lygus bugs have also been noted in sunflower fields. Diamondback moth larvae in canola remains a concern for growers and agronomists in the Eastern region, with lots of scouting and some limited insecticide applications occurring.”