By Daphne Cruise, PAg., Crops Extension Specialist
Cutworm damage can occur in varying severity throughout a field. There have been reports this year of increased cutworm presence on soybean stubble. This is partly due to the fact that soybean maturity is later than most crops, which means the crop stays green and flowers later, making it an attractive spot for adult moths to lay their eggs. A drier spring is also advantageous for some cutworm species, especially for those species that overwinter as eggs.
Be sure to scout the field and look for cutworm damage, which tends to start on hilltops and south-facing slopes. Scout fields in the evening or very early in the morning to look for above-ground feeding cutworms. Some cutworm species will sever plants at the ground level and some species prefer stem and foliar feeding higher up on the plant. Start to scout at the edges of the patch where the last living plants were; new cutworm feeding should be here. Cutworms will often move from plant to plant amongst the loose soil in the seed row. Dig up about two inches of soil, looking for larvae that curl up or attempt to hide amongst soil debris (if soil moisture is down farther than two inches, you may have to dig deeper to find larvae, especially during the day). Remember, other issues such as disease or poor germination due to dry conditions could be the cause of bare patches in the field, as well.
Identifying the species of cutworm is important, as this will determine your options and if control is warranted. There are different economic thresholds depending on the species and crop. For assistance in identifying cutworm species and economic thresholds, call the Agriculture Knowledge Centre at 1-866-457-2377 or refer to “Cutworm Pests of Crops on the Canadian Prairies.”
Although most species will feed on above-ground foliage, pale western and red backed cutworms do most of the damage at older larval stages when they feed at the soil surface, cutting off plants. They are less likely to come into contact with a pesticide. A systemic product, such as a seed treatment or systemic insecticide, may provide the best control. Dingy cutworms do most of their feeding on plant leaves, and so a contact pesticide is an option. Dingy cutworm overwinter as larvae and so are often seen early in the spring.
- If there are birds gathered in a particular area in the field, this may be a good place to start looking for cutworms.
- If control is warranted, do so as close to nightfall as possible, as this is the time when cutworms will come up to feed.
- Squeeze a few cutworms. Green insides mean they are actively feeding. Brown insides mean they have stopped feeding. However, this is tricky since they may have stopped feeding as they are about to pupate (at which time they will not cause any more damage), or they are moulting between instars, which means they will continue to feed. Residual activity of most insecticides should help to control them when they do start feeding again.