By Kaeley Kindrachuk, B.App.Sc., AT, Crops Extension Specialist and James Tansey, PhD, Provincial Specialist, Insect/Pest Management
The Crop Walk on May 29 brought us to a newly emerging pea field to talk about the pea leaf weevil. The pea leaf weevil is a short-snouted, invasive weevil. They have been continuing to move east and north since they were first documented in Alberta in 2000. The movement of this insect north seems to be limited by cold temperatures, but they have been documented as far north as Saskatoon. As well, they have been documented eastward near the Saskatoon/Manitoba border. The pea leaf weevil is a relatively small insect, about 3.5 to five mm long as an adult. This time of year, adults will be present. They have stripes from their head to the bottom of their abdomen (photo 1). Adult weevils are very difficult to see, but damage caused by the adult weevils is easier to find. They feed from the edge of the leaf, resulting in characteristic notching. Adult weevil feeding can result in crop damage, but the most significant damage will come from the larvae. Females can lay up to 24 eggs per day, and they drop eggs as they invade a field. She can produce up to 1,500 eggs in her lifetime. The larvae will feed on nodules on the roots. The concern with these insect pests is early on in the growing season. They overwinter as adults in shelterbelts and similar areas and tend to invade from the field edge. Seed treatment is still the best course of action against these pests.
When producers and agronomists are scouting for pea leaf weevil, it’s important to do it early, from the two to six node stage. Once the crop is past the six node stage, it’s less susceptible to larval feeding. Adults will emerge at the same time, and can engage in a springtime flight, which means they can be found deeper in a field, although invading from the field edge is more common. When scouting for notch feeding, start about two meters into the field and look at about 10 to 20 plants in five places (25 meters apart), staying two meters from the field edge. Then do the same thing about 100 meters in. The more scouting that’s done, the better the data that will be collected. The annual survey is starting right now, and collaborators between the Ministry of Agriculture, Agriculture and Agri-Food Canada, and the Saskatchewan Association of Rural Municipalities’ (SARM) Plant Health Officers will be out surveying. The survey is done in transects from west to east. Two fields per rural municipality are surveyed starting on the west side of the province, continuing until there are no notches found. When looking for notching, it’s important to actually have a look at the crop, as sometimes damage from other insects can be confused with notching from the pea leaf weevil. Data is collected by the Ministry and released as a pest forecast map (photo 2). Updates can also be found through the Prairie Pest Monitoring Network.
For more information, visit our pea leaf weevil webpage, check the Prairie Pest Monitoring Network Blog or contact your nearest Crops Extension Specialist.