2026 Black Cutworm Cutting Predictions

Black cutworm (BCW) is a migratory pest that arrives in Iowa with spring storms each year. Black cutworm moths lay eggs in and near crop fields, and larvae can feed on leaves or cut seedlings of corn, soybean, and other plants. Black cutworm infestations are unpredictable, making it essential to scout to determine whether BCW larvae are present in a field and if management is required. Although planting is delayed compared to recent years, there will likely be some BCW larvae present in fields once crops begin to emerge. Black cutworm migrations will continue to occur and pose a continued risk. 

Larvae must attain a certain size (4^th instar) to be large enough to cut corn plants, and cutting can occur until plants reach the V5 stage (5 visible leaf collars). Use the predicted cutting dates in this article as a guide and plan to scout fields once crops emerge. Fields with cover crops, volunteer plants, or weeds this spring should be prioritized since they serve as egg-laying sites for migrating moths. It is not economical to use preventative insecticide applications; however, rescue treatments can be very effective if scouting detects larvae at economic levels.

Predicting cutting dates

We can predict when BCW will reach the 4^th instar based on accumulating degree days and the occurrence of significant flights. A significant flight is defined as the capture of eight or more BCW moths in a pheromone trap over a two-night period. Larvae reach the 4^th instar after 300 GDD have accumulated since a significant flight.

The Iowa Moth Trapping Network enlists the help of volunteers around the state to monitor BCW activity annually. You can find more details about the network in the first report. Figure 1 shows the predicted cutting dates for BCW in each crop reporting district. These cutting dates are estimated by combining actual, historical, and forecasted degree day data. Lighter colored counties are where black cutworm traps are monitored in 2026, while counties with hash marks indicate where significant flights have occurred to date.

Remember: these cutting date predictions are estimates based on reported moth captures. We recommend scouting fields for BCW larvae once crops begin to emerge, especially in southern Iowa, where predicted cutting dates have already passed. Capturing moths in a pheromone trap does not necessarily mean economic infestations will occur in a particular location. 

Scouting is the only way to determine if BCW are present and whether management is warranted. Combine scouting for BCW with early-season stand assessments. Missing or cut plants are signs of black cutworm feeding, but dig in the soil near affected plants to confirm larvae are present. Other early-season pests (grubs, seedcorn maggot, wireworms) may also be present. Refer to the black cutworm encyclopedia article to learn more about black cutworm identification, biology, scouting, and management.

Keep up with moth flights!

Black cutworm trapping will continue throughout May, and any additional significant flights that occur will be included in our weekly ICM Blog updates. Additional significant flights in an area indicate a potential for prolonged feeding of BCW larvae, so continue to scout until corn reaches V5.

If you live near the Iowa border, information from trapping networks in other states may be useful to you. Some links to out-of-state resources are listed below, but others may be available:

• University of Minnesota 
• University of Missouri
• University of Illinois
• University of Nebraska-Lincoln
• Great Lakes and Maritimes Pest Monitoring Network

Report larvae!

If you see any fields with BCW larvae or injury while scouting, please let us know! You can contact us via email (bugtraps@iastate.edu) or X (formerly Twitter; @ErinHodgson_ISU and @AshleyN_Dean). This information will help us refine cutting predictions and scouting recommendations in the future.