If the crop is experiencing moisture stress then the effects of cutworm damage will be more dramatic. If plants are not drought stressed and appear healthy and vigorous then insecticide treatment is justified when there are 4 to 5 army cutworm larvae per square foot. Treatment is justified for pale western cutworms when 2 to 3 larvae per foot of row are present. However, under drought conditions, treatment may be justified at lower cutworm larvae populations. Prior to making a decision to treat a field it is important to determine the size of the larvae.
Large larvae indicate completion of the feeding or damaging stage of cutworms.
When this happens the majority of the damage has been done and a treatment may not be cost effective. In new seedling stands 2 cutworm larvae per square foot cause economic damage. The economic threshold is quite low because seedling canola plants have little ability to compensate for damage. Treatment can be justified at 0.3 to 0.5 cutworm per square foot. Because sugar beets emerge and grow slowly during early establishment, cutworms can drastically reduce a sugar beet stand in a short period of time.