By Nicole Montreuil, AAg, Crops Extension Specialist, Outlook
The 2021 growing season posed many challenges for farmers, some of which included high insect pest pressure. Several insect surveys took place in 2021 with populations varying significantly depending on the insect species. This article provides a brief overview of our Provincial Insect/Pest Management Specialist James Tansey’s webinar on the 2021 insect populations and what we could see going into 2022.
Only three to four of the 85 species of grasshoppers are pests. Most of the species in Saskatchewan are non-pest species. Some features of non-pest grasshopper species can be identified if they have wings before late June or if they have brightly-coloured hind wings. The pest species fall under three broad groups and they all have short antennae. Spur-throated grasshoppers have a spur characteristic on their throats. Their face is vertical or only slightly slanted and the top of their head is rounded. The three main species are the migratory grasshopper, Packard’s grasshopper and the two-striped grasshopper. Banded-winged grasshoppers can be pests as well, but only one of the species, the clear-winged grasshopper, is typically a problem.
The hot, dry conditions the province experienced this year was beneficial to the grasshopper population. Grasshopper numbers increased from 2021 and many incidents of spraying, in many crops, were reported throughout the province. Areas of light risk were observed in scattered areas of the province which can be viewed in the 2022 Grasshopper Risk Forecast Map.
Wheat midge had decreased densities over 2021 and were only seen in regions that had adequate rains. Spraying for midge in 2021 was very rare. Dry conditions reduce populations as they overwinter as larvae in the soil and need soil moisture to pupate. If they don’t receive moisture, they can overwinter for another year. Major yield loss can occur when seeing >600/m².
Barley thrips were found on barley and occasionally durum in mid-late June/early July in the Regina, Weyburn and Tisdale regions. There were several reports of control required, with dimethoate being used. Threshold for barley thrips are seven to eight per stem and take a keen eye to see as they are very small.
These insects are monitored in early June to early August with pheromone traps. There were 310 traps set in 2021. There was a mean catch of 91 which is considerably lower than the last three years. Only one trap was recorded with >400 bertha armyworms in the Loreburn area with no reports of spraying in the province. Outbreaks happen cyclically every six to eight years with the last one being in 2012-2013 and a minor outbreak in 2015-2016.
Cabbage Seedpod Weevil
In 2021 populations were low overall, except in southwest Saskatchewan where there were higher numbers and some reports of spraying. Cabbage seedpod weevils are invasive and their range continues to expand. Scouting for cabbage seedpod weevil should begin when the crop is at the bud stage and continue through flowering. Select 10 locations within each field and using a sweep net count the number of weevils in 10 180-degree sweeps. For an accurate estimate of weevil numbers in a field, sweeping should occur both in the field perimeter and interior. The economic threshold is when an average of 25 to 40 weevils are collected in the 10 sweeps. If an insecticide application is warranted, the best time to spray is when crops are in 10 to 20 per cent flower. This will prevent eggs from being laid in newly formed pods.
In 2021, traps began to capture in early May and numbers increased until mid-June. Cumulative capture numbers ranged from zero (most sites) to 11. There were low numbers and no reports of spraying. In the late season (mid-October) record numbers of larvae and pupae in late-seeded canola were reported around Kindersley. Diamondback moths are migratory and fly up from Texas, Florida and Mexico. They can travel 1000 km/day and rain down on sites in Western Canada. Their early arrival allows for reproduction and population increases as females can lay up to 176 eggs each.
In Saskatchewan we mostly see red-backed and some pale western cutworms. Damage was reported in May-June with reports of spraying. Both species favour dry conditions and the females are attracted to uncultivated fields with broadleaf weeds in the fall to lay their eggs.
Flea beetles are a common insect pest for canola and mustard producers across the prairies. The two main species are the striped flea beetle and the crucifer flea beetle. Northern regions are dominated by striped flea beetles that prefer cooler, moist conditions, while crucifer flea beetles are dominant in southern regions of the province. In 2021, there was widespread serious damage in the northeast. In the Tisdale region there were two and sometimes three insecticide applications. Overall, there was a lot of spraying and reseeding being done. Fall populations of crucifer were high in Swift Current, Regina and Outlook areas. What this means for 2022 is uncertain. If the temperature is right, flea beetles can have two generations per year. Looking at fall numbers and predicting what we will see in spring 2022 is not well understood. There was some indication that very hot conditions may have limited the striped flea beetles’ late-summer activity and survival.
Lygus bugs are piercing, sucking feeders and have a salivary protein, polygalacturonase, that causes more damage than the physical feeding. They have a broad host range of over 300 species. There were many reports in 2021 in canola, flax and legumes. The adults emerge from plant litter after snow melt, and after mating, females seek budding alfalfa or canola. Egg laying can occur in May, June and July with first nymphs normally appearing in May. Populations are influenced by temperatures as they like warmth. There were a few identification issues this year, as early instars of lygus look a lot like pea aphid. Some helpful identification tips are to look for wings starting to develop on the backs of the insect for lygus and if they are scurrying around fast, they are lygus. If they are moving like their feet are stuck in mud, they are pea aphid. Pea aphids also have more of a round head while lygus has a pointed tip like a nose.
Canola Flower Midge
There was no survey done in 2021 due to travel restrictions. There were some reports of canola flower midge, but populations were generally low and no economic thresholds were met. There were some larvae that showed up in canola pods later in the season.
In 2021, there were reports in seedling canola and flax of bare patches in southern Saskatchewan. They have a very broad host range and can be found in high numbers just below the soil surface. The nymphs, which are red, aggregate above ground and feed on epicotyl, seedling stem and leaves. The adults feed on the seeds underground.
Pea Leaf Weevil
Surveys for this insect are done in pea crops covering most of the growing region in the province. Numbers in 2021 increased from 2020 but were still considered low. The pea leaf weevil is considered an invasive insect and its range continues to expand. Signs of pea leaf weevil in the crop are feeding notches in the plant. Modeling indicates they are susceptible to cold temps and low snow cover. Seed treatment is the best defense against this insect as foliar insecticides are not recommended.
Pea aphids feed on peas, beans and lentils. There was relatively low pressure in 2021 with no reports of spraying. There continues to be work on economic thresholds and insecticide timing. Predation and mortality increase with temperature. Juvenile mortality is highest at 27 C with only a nine per cent survival rate.
Spotted Wing Drosophila
This pest was first reported in Saskatchewan in 2019. It has a very broad host range of raspberry, strawberry, cherry, blueberry, plum, saskatoon, haskap and tomatoes. The female lays eggs under the skin of healthy ripening fruit causing it to become prematurely soft and unmarketable. In 2021, it was found in 20 orchard sites in Saskatchewan.