Hunting for stalk borers

June 15, 2022 12:12 PM
Blog Post

While in westcentral Iowa yesterday setting up some small plot experiments, I got distracted by a long stretch of grass alongside a cornfield. I noticed some “deadheads” among the green plants and decided to dig a little deeper.

brome grass.

I pulled up some of the dead head plants and noted holes about half-way down the plant.

stalk borer hole.

I used a knife to spilt the stalk just above the hole and a very unhappy caterpillar was inside.

stalk borer.

The caterpillar, known as common stalk borer, was about an inch in length and had a purple “saddle” on the thorax and an obvious orange head. Yes, I am taking donations for a moisturizing hand cream!

stalk borer.

The caterpillar pretty much filled up the inside of the stem and had created copious amounts of sawdust-like frass.

stalk borer frass.

Based on accumulating degree days estimated by a recent ICM News article, I would expect stalk borers to move to corn and soybean in central Iowa next week. The only time to act is when the caterpillars are exposed, moving from grass to crops. Take a look at field edges now, especially in areas with previous stalk borer infestations.


Erin Hodgson Professor

Dr. Erin Hodgson started working in the Department of Entomology, now the Department of Plant Pathology, Entomology, and Microbiology, at Iowa State University in 2009. She is a professor with extension and research responsibilities in corn and soybeans. She has a general background in integrated...