Wallaces Farmer

Get ready for corn rootworm

Scouting this summer can save future headaches.

Gil Gullickson, editor of Wallaces Farmer

May 23, 2024

2 Min Read
corn rootworm larvae
DAMAGING LARVAE: Each year, corn rootworm larvae munch on corn roots, causing over $1 billion in damage.Courtesy of Corteva Agroscience

If you’ve ever wondered if soil-applied insecticides for corn rootworm work, read this.

Kurt Maertens was digging up corn roots in an east-central Illinois field while working as a crop scout during college.

“I was digging up plants with the roots eaten off on just one side,” says Maertens, who now works as a BASF technical services representative. “At first, I went, ‘Wow.’ But we tracked it down to the day that the farmer was planting the field. He was applying a soil-applied insecticide, and it was a real windy day. It was blowing so much that it blew the dry insecticide to just one side of the row. So, the roots that were shredded were the ones not protected.”

Granted, it was too late to do anything about it during the root dig. Still, it revealed what was occurring in the field so those plants could be harvested as soon as possible that fall.

Revealing root digs

Root digs also reveal if other maladies are occurring, such as resistance to traits or crop rotation. It's important to note, though, that traits and crop rotation still work in many cases. In some cases, however, performance can vary even within a farm.

“You may have corn rootworm in one field but might not have it in a field across the road,” says Maertens. “The only way you can find out is to dig roots later this summer.”

Yellow sticky traps may be used to predict next year’s infestations. These traps nab beetles flying around when they are laying eggs later in the growing season.

Due to a recent dry growing season, rootworm populations have been building. “We’ve had some traps from north-central Iowa that average 20 adult beetles per trap per day,” Maertens says. “The threshold starts at two beetles per trap per day. That tells you that there is some significant yield damage being done.” 

If rains continue, farmers may catch a rootworm break in 2024.

“One thing that really limits [rootworm larval] survival is rainfall,” says Jesse Grote, Syngenta agronomic services representative. “They don’t like saturated soils at all. The rainfall we received in April and much of May will help.

“No one wants to dig roots when corn is in the middle of flowering,” he adds. “But if there was rootworm pressure last year in a field, especially in continuous corn, I would want to be out scouting cornfields and digging roots in July.”

About the Author(s)

Gil Gullickson

editor of Wallaces Farmer, Farm Progress

Gil Gullickson grew up on a farm that he now owns near Langford, S.D., and graduated with an agronomy degree from South Dakota State University. Earlier in his career, he spent 13 years as a Farm Progress editor, covering Minnesota and the Dakotas.

Gullickson is a widely respected and decorated ag journalist, earning the Agricultural Communicators Network writing award for Writer of the Year three times, and winning Story of the Year four times. He is a past winner of the International Federation of Agricultural Journalists’ Food and Agriculture Organization Award for Food Security. He has served as president of both ACN and the North American Agricultural Journalists.

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