The first-round of nasty storms that hit the southern states in mid-April brought record numbers of black cutworm moths our way (see “Black Cutworm Trap Comparisons, 2006–2011”). Delayed planting, coupled with significant egg laying in weedy fields combine to have potential for significant cutworm damage within the week.
We track the development of the black cutworm from the time of an intensive capture (mid-April) to predict first cutting/damage (refer to accompanying map). Based on the growth development model, it takes approximately 300 heat units (above the 50?F base) from egg hatch to the stage when black cutworm larvae begin to cut plants. Leaf injury, though less noticeable, will likely be present before cutting, as this is done by smaller larvae. Using pheromone trapping of moths and tracking of heat unit accumulations for first cutting is not an exact science, but they do give us a good indication of what to expect and when to start looking. However, it is not possible to predict if individual fields will be infested.
With many areas of Indiana just planted, or being planted now, moths may have found these weedy fields as an ideal egg-laying site. Tillage at, or just before, planting will provide little control of the eggs or newly hatched larvae – it will mostly serve to move them around a bit. Since black cutworm has been a minor pest the past several years, producers may have a false sense of security with the seed-applied insecticides and/or Bt-corn. The lack of damage during these past years has been more due to the record early dates for corn planting combined with low black cutworm arrivals. This combination has been ideal for limiting black cutworm risk.
We’ve heard that many fields are being treated with a foliar insecticide at the time of herbicide burn-down. We can understand the proactive approach, especially with the delayed planting. Understand that these insecticides have their limitations, specifically when subjected to sunlight, rainfall, heat, and dust. Claims of multiple weeks of control with foliar insecticides in spring conditions are simply unfounded; 7-10 days of control is the most optimistic measure. Remember that these are contact insecticides, and as soon as they hit the soil, breakdown begins. Some good news: as soil temperatures rise with the sudden surge in temperatures, corn should emerge and grow quickly. We can manage this pest effectively and have done so in the past: Timely scouting and rescue foliar insecticides when necessary are the tried and true approach with black cutworm. Happy scouting!