Begin Scouting for Black Cutworm in Corn

Black cutworm (BCW) is a migratory pest that arrives in Iowa with spring storms each year. It is sporadic and unpredictable, making it essential to scout to determine whether BCW larvae are present in a field and management is required. Because BCW is sporadic, it is usually not economical to use preventative insecticide applications; however, rescue treatments can be very effective if scouting reveals larvae are present. Even though cool, wet conditions have slowed planting progress throughout the state, BCW development is on track with previous years.

It may be even more important to scout this year, because delayed planting may result in the “perfect storm” for BCW injury: small corn plants (less than V5) in the field at the time larvae are large enough to cut corn plants. Moth flights into Iowa will continue throughout the month, so prolonged feeding may occur on young corn plants. Scouting for BCW larvae can be combined with early season stand assessments or scouting for other pests.

Predicting cutting dates

BCW moths lay eggs in and near crop fields, and larvae can feed on leaves or cut corn seedlings. 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. We can predict when BCW will reach the 4^th instar based on accumulating degree days and when a significant flight occurred. A significant flight occurs when eight or more BCW moths are captured over a two-night period in a pheromone trap. The Iowa Moth Trapping Network enlists the help of volunteers around the state to monitor BCW activity annually. You can keep up with the Iowa Moth Trapping Network with weekly updates posted to the ICM Blog.

Significant flights have occurred in most areas of the state. Counties that have reported significant flights include Taylor (April 13 and May 4), Buena Vista (April 22), Mills (April 22), Marshall (April 24), Mahaska (April 24 and May 4), Washington (April 24, April 29, and May 6), Lucas (April 29), Hamilton (May 2), Benton (May 5), and Polk (May 5).

Figure 1 shows the predicted cutting dates for BCW in each crop reporting district. These cutting dates are estimated by combining actual and historical GDD data. BCW trapping will continue throughout May, and any additional peak flights that occur will be included in our weekly ICM Blog updates.

Capturing BCW moths in a pheromone trap does not necessarily mean there will be economic infestations in a particular location. Scouting fields is the only way to determine if BCW are present and whether management is warranted. 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:

• Subscribe to the ICM Blog and read the weekly updates.
• Go to https://corn.ipmpipe.org/insects/ to see true armyworm and BCW maps with reports from Iowa, Illinois, and Wisconsin.

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

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 Twitter (@erinwhodgson and @ashleyn_dean). This information will help us refine cutting predictions and scouting recommendations in the future.