Figure 1. Western bean cutworm egg mass on upper leaves of vegetative stage corn (Photo by Nicole Carutis, Penn State Extension)
Producers encouraged to be on the lookout for caterpillars and egg masses and consider the presence and type of Bt corn.
For about six years straight, Penn State Extension and the Department of Entomology trapped for western bean cutworm to try to understand the population dynamics of this species, which we first found in Pennsylvania in 2009. We discontinued this effort in 2016, because, even though we could find moths, we could not find many caterpillars. Populations of this potential pest of corn and dry and snap beans have been mild in Pennsylvania, particularly compared to NY, MI, OH, WI, and Ontario, where this pest has caused economic damage.
This year at our research farm in Centre County I have easily found egg masses on upper leaves of vegetative stage corn (Figure 1), leading me to believe that this pest species is more common than in previous years. I must admit that I am not sure what this means because this caterpillar prefers to feed upon reproductive stage corn, particularly on the tassel and on the developing year. Given that much of our corn is delayed this year compared to most years, perhaps this is a good thing in terms of reducing the potential for damage. Nevertheless, I encourage folks to be on the lookout for these caterpillars in their corn fields. You should also be aware that some of the Bt corn that used to be able to help control populations of this caterpillar have not been performing very well in surrounding states; we addressed this issue in a previous article. The caterpillars looks similar to corn earworm, but does not have lines down the sides of its body like corn earworm does and has three distinct light-brown lines on its "neck" just behind its head (Figure 2).
Figure 2. Western bean cutworm caterpillar with the distinct brown lines on its "neck." (Photo by Eric Bohnenblust, Penn State Department of Entomology).