I.D. worms in silks and ears

This year’s Western Bean Cutworm (WBC) flight in northern Indiana counties has been quite impressive. Though it is not over, by looking at the moth captures the past couple weeks we are past peak flight. Most eggs have been laid by this point, and there were many.

We are aware that many fields have been scouted, found over the 5% threshold, and subsequently treated with insecticide. In the next weeks, folks will be out to determine the extent of damaged ears, if any, are present in fields.

The distinguishing characteristics between mature western bean cutworm and corn earworm (CEW) larvae are found below. It is a little trickier to determine species when the larvae are small, i.e., early instars.

For small caterpillars, you must use skin texture: WBC being smooth and CEW being bumpy. This requires a 10X magnifying lens.

Not to add to the confusion, but there are a couple other caterpillars, fall armyworm and European corn borer, that also may be found in the ear. For now though, we will keep it to the two most likely suspects.

As we enter later summer, caterpillars will be larger, more obvious and easier to tell apart. We will check back in at that time with another report. Happy scouting!

Western bean cutworm identifiers.

Corn earworm identifiers.

Western Bean Cutworm Identification photo

Early to late instars of the western bean cutworm. Notice that the distinctive “black rectangles” are lacking on the young larvae.


Source: Perdue Crop & Pest Newsletter. By John Obermeyer and Christian Krupke, Purdue University Entomologists