By Ashley Dean and Erin Hodgson
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 (4th 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 4th 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 4th 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.
Source : iastate.edu