Damage from Western Bean Cutworm in Your Corn Fields?

Western bean cutworm (WBC) has been a confusing pest species for me and, perhaps, for corn growers in Pennsylvania.  Moths of this species lay eggs in June, July, and August, and their caterpillars feed on reproductive tissue of corn, particularly the tassel and the developing ear. Historically, this pest species has been a challenge for corn growers in Nebraska and other western states, but in the early 2000s, it started to spread eastward.

Using pheromone traps, we first found WBC moths in Pennsylvania in 2009, and we then trapped for them annually from 2009 to 2015. We discontinued this effort in 2016 because, even though we were finding moths, we could not find significant populations of caterpillars in nearby corn fields. At the same time, populations of moths in other states (e.g., New York, Michigan, Ohio, Wisconsin) and provinces (Ontario) in the region were large, and entomologists in those areas were regularly encountering economic damage in corn and dry and snap beans. 

During the summer of 2025, we restarted our trapping efforts for WBC to understand if their abundance had increased and to see if we could find infestations in fields. Extension educators trapped moths during July and August across ten counties, and we reported our data to the Great Lakes and Maritimes Pest Monitoring Network, which is operated by Ontario's Ministry of Agriculture, Food and Rural Affairs.  You can see the data for WBC displayed on this webpage.

We captured moths in early July and into August, but very few compared to other states and Ontario, and again we have not found fields infested with WBC caterpillars. Now, as harvest approaches, we are curious what folks are finding around Pennsylvania; therefore, I encourage farmers and scouts to be on the lookout for these caterpillars in corn ears. If you find fields with substantial numbers of ears infested with WBC caterpillars, we would be interested in hearing from you (you can contact me directly or contact your local agronomy educator with Penn State Extension).

WBC caterpillars look similar to corn earworm, but do not have lines down the sides of their bodies like corn earworm and fall armyworm do; WBC caterpillars also have three distinct light-brown lines on their "neck" just behind their head (Figure 2).  We hope to hear from you as we try to figure out the risk this pest species poses to Pennsylvania corn production. Thanks!