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Plan soybean fungicides now

You look at current commodity prices and recheck your crop budget. It’s possible you may need to trim costs. If you still want to make sure your soybeans are protected as much as possible, where do you put those limited dollars you can spend on fungicides?

The key is to know how susceptible different varieties you have planted are to specific diseases, notes Betsy Bower, agronomist with Ceres Solutions, Terre Haute. She would pay most attention to Septoria brown spot, frogeye leaf spot and anthracnose. Remember that fungicides don’t stop all soybean diseases.

Key Points

• Find out whether your varieties are susceptible to leaf spot, brown spot.

• Check for the presence of disease before spraying.

• Target the application to your most susceptible fields.


“Go back to the person who sold you the soybeans,” says Steve Dlugosz, a crops consultant for Harvestland Co-op in east-central Indiana. Both Bower and Dlugosz are members of the Indiana Certified Crop Advisers group.

“The person who sold you the soybeans should have a more thorough understanding of the strengths and weaknesses of the lineup,” Dlugosz continues.

To spray or not to spray

For Bryan Overstreet, a Purdue University Extension ag educator in Jasper and Pulaski counties, also a CCA, it comes down to brown spot and frogeye leaf spot. “I would see if any of the varieties I planted have resistance to these diseases,” he says. “If they do, I would not spray those varieties.”

Suppose your varieties aren’t resistant. Bower still recommends checking for the presence of disease before spraying. “If disease isn’t present, I would consider protecting soybeans in fields most susceptible to disease development, like seed beans, irrigated beans or soybeans along river bottoms or in low-lying fields. Humidity is often highest in low-lying fields along streams, and that favors disease development.

“I would also consider spraying poorly drained fields, or fields with heavy soils, and fields where soybeans were planted back-to-back. Finally, I would spray fields with excellent yield potential,” Bower says.

The window for spraying is narrow one

Betsy Bower says there’s a relatively narrow window for spraying fungicides on soybeans.

“Fungicide timing should be somewhere from R2, which is full flower, and R4, which is full pod,” she says. “I have observed more consistent yield responses at the R3 to R4 stage of soybean development. But check the label of the product you intend to use.”

Steve Dlugosz agrees. He has seen the most consistent results at R3. That’s the beginning of pod fill.

It’s the same stage Bryan Overstreet prefers for seeing fungicides applied. The pod is 5 millimeters long at one of the four uppermost nodes on the main stem, with a fully developed leaf.


This article published in the June, 2010 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.