Cutworms are showing up in big numbers in some fields across the Prairies, particularly in northeastern Alberta. Check emerged canola crops for bare patches, holes or notches in foliage, and clipped plants — telltale signs of cutworm feeding.
At least four cutworm specifies may damage canola: pale western, redbacked, army and dingy. Dingy and army cutworms overwinter as larvae, so early in the season they will be larger than species that overwinter as eggs. You’re more likely to see bare patches, not clipped plants, with dingy species.
Many species of cutworms can feed for several weeks. If they thin out a crop early, reseeding may not be the best solution if the larvae are young enough that they could still be feeding when the new crop emerges. A lot of glassy cutworms have been found in the Peace region, but this species tends to feed on cereals and stay away from canola.
Current canola seed treatments are not registered for or known to provide adequate control of cutworms, but many foliar insecticides are registered. Cutworms surface at night to do their above ground feeding, so spraying as close to nightfall as possible is recommended. Since not all cutworms will surface on a single night, it may take several days before full effect of the insecticide is achieved.
Scout before spraying. Dig in the ground to a depth of 10 cm and look for cutworms and wireworms. Wireworms can cause similar bald patches to appear in canola fields, but no products are registered (or effective) for wireworm control in canola. Wireworms are a higher risk in canola seeded into land that was in pasture or hayland last year. If wireworms are the culprit, put away the sprayer and make note of areas or fields where the damage was higher. Remember these areas when planning crops and seed treatments for next year.
Click here for a MAFRI factsheet on cutworms, which includes photos. Click here to view the Canola Council of Canada’s cutworm webinar from last week.