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 over a two-night period in a pheromone trap. 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. Counties that have reported significant flights include Floyd (April 8), Muscatine (April 11), Benton (April 15), Marshall (April 17), Keokuk (April 19), O’Brien (April 19), Iowa (April 25), Buena Vista (April 25), Washington (April 29), and Boone (April 29); the date in parentheses is the date of the first significant flight in that county.
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. Accurate cutting date predictions rely on the presence of moth traps in each region; therefore, it is important to scout well before these predicted cutting dates to ensure larvae are noticed before plants are cut. BCW 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 may represent prolonged feeding of BCW larvae, so continue to scout until corn reaches V5.

Figure 1. Estimated black cutworm cutting dates for each Iowa crop reporting district based on initial significant flights in 2024, as of May 6. These are estimates of when cutting will begin, but additional large flights may result in prolonged feeding by black cutworm larvae.
Capturing BCW moths in a pheromone trap does not necessarily mean economic infestations will occur in a particular location. Scouting fields 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 this encyclopedia article to learn more about black cutworm identification, biology, scouting, and management.
Keep up with moth flights!
You can keep up with the Iowa Moth Trapping Network in a few ways:
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:
Source : iastate.edu