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Make sure the risk is worth the reward before skimping on rootworm protection.

Tom Bechman 1, Editor, Indiana Prairie Farm

April 9, 2016

3 Min Read

You’re wondering if you can skimp on corn rootworm control to save money. If you do,

setting the stage for what comes next are Jesse Grogan, LG Seeds agronomist, Lafayette; Tom Stein, Ceres Solutions, branch manager at Boswell/Templeton; and Greg Kneubuhler, owner of G & K Concepts, Harlan. All three are Indiana Certified Crops Advisers.

Question: I left off the GMO rootworm trait to save money. I’m not applying a soil insecticide either. I use conventional tillage and plant after soybeans. How should I watch for rootworms? When? Remedies?

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Grogan: One usually learns of potential rootworm pressure by looking for adults in the previous crop year. This should be done each year at silking stages in corn, and in late July through August for soybeans. There are no ‘good’ in-season rescue treatments.

Stein: Scouting for corn rootworm larvae should begin when the larvae are hatched and actively feeding on corn. Generally speaking, 50% larval hatch occurs when soils have accumulated about 700 growing degree day heat units. The warmer the soil is, the earlier the hatch will be. Dig 10 or more roots from different areas of the field.

Grogan: Yes, one can dig plants in June according to hatch date to look for young larvae in suspect areas. But who is going to do that?  

Related: Bt resistant rootworm: Now what?

Stein: If you dig, there are a couple of different methods to determine infestation levels. One is placing roots in a bucket of water and washing away soil. Larvae float to the surface. The other is hand sorting by placing the root ball on a piece of black plastic and breaking away the soil. Count the average larvae per plant. If you find eight or more by washing roots or two or more by hand sorting, consider a rescue treatment.

Kneubuhler: If two or more larvae are found per plant, treatment can be warranted, but efficacy is poor. An insecticide applied at the base of the plant is the only option.

Grogan: Yes. A lay-by insecticide treatment is possible, but few are set up for it. Timing of insecticide application is critical. It needs to be within a seven to 10 day window when larvae are in the juvenile stage. Rescue operations are very limited.

Related: Options to protect from corn rootworm

Stein: There are several insecticides labeled for rescue treatments, but none are very effective. They require either a lay-by cultivator application applied to both sides of the row ahead of the cultivator, assuming you have a cultivator, and assuming field conditions allow it. You can also do a chemigation application if you have irrigation. Either method requires enough moisture to wet the root zone to the depth of the corn rootworm larvae where control is needed.

About the Author(s)

Tom Bechman 1

Editor, Indiana Prairie Farm

Tom Bechman is an important cog in the Farm Progress machinery. In addition to serving as editor of Indiana Prairie Farmer, Tom is nationally known for his coverage of Midwest agronomy, conservation, no-till farming, farm management, farm safety, high-tech farming and personal property tax relief. His byline appears monthly in many of the 18 state and regional farm magazines published by Farm Progress.

"I consider it my responsibility and opportunity as a farm magazine editor to supply useful information that will help today's farm families survive and thrive," the veteran editor says.

Tom graduated from Whiteland (Ind.) High School, earned his B.S. in animal science and agricultural education from Purdue University in 1975 and an M.S. in dairy nutrition two years later. He first joined the magazine as a field editor in 1981 after four years as a vocational agriculture teacher.

Tom enjoys interacting with farm families, university specialists and industry leaders, gathering and sifting through loads of information available in agriculture today. "Whenever I find a new idea or a new thought that could either improve someone's life or their income, I consider it a personal challenge to discover how to present it in the most useful form, " he says.

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