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Help for soybean insecticide decisionsHelp for soybean insecticide decisions

A new study looks at the economics of spraying insecticides in soybeans.

Tom J. Bechman, Midwest Crops Editor

January 24, 2025

3 Min Read
A brown marmorated stinkbug on a soybean leaf
FIND INSECTS? If you find insects, first, identify them. This one is a brown marmorated stinkbug. Then ask questions. How many are there? Is spraying justified? Because there were only a few here, spraying wasn’t considered. Tom J. Bechman

Scouting soybeans means looking for many things, including insects. Just because you find insects doesn’t mean spraying is justified. Steve Gauck finds everything from bean leaf beetles to grasshoppers to green and brown stinkbugs.

“When you find them, numbers and potential for damage are important considerations,” says Gauck, a regional agronomy manager for Beck’s, based near Greensburg, Ind. “If it is early or midseason, we evaluate potential for leaf loss. It takes a lot of defoliation to threaten soybean yield, but the percentage soybeans can stand before treating decreases during the reproductive period.

“The other concern is potential pod feeding late in the season. Stinkbugs can penetrate pods, stinging beans and opening pods to secondary infections. That is why we monitor insects all season long.”

To spray or not to spray?

Scouting and monitoring is one thing. Spraying insecticides for prevention or control is another. Nick Seiter, Extension field crop entomologist at the University of Illinois, initiated field trials in 2024 to assess if insecticide application in soybeans pays.

Trials were established at various sites in Illinois. Insect populations were below threshold levels for any insect at all locations in the first year of the study.

Related:Will aphids threaten corn yields in ’25?

Seiter takes a closer look at the study and insect management in soybeans in this exclusive interview:

Is there value to insecticides if you don’t have pests when you spray? From your results so far, it looks like the answer is no. Generally speaking, there is no value to this practice. However, that is what we’re trying to determine with this research. In year one, we had low populations of insect pests at all sites. As a result, insecticide applications did not pay off in preserved yield.

What insects did you expect to see, or did you see? The pests we see most frequently include bean leaf beetles, stinkbugs, green cloverworm and similar pests.

Is there a best time to consider spraying insecticides in soybeans? Is the R5 stage too late? This depends on if and when an economically damaging insect pest population arrives. Most fields in an average year do not have such a population. Timing when they do occur is species- and season-dependent. One limitation of a growth-stage-based approach, where you would spray based on growth stage of soybeans, is that residual activity of most insecticides is short.

We only kill what’s in the field at the time of application and perhaps for seven to 10 days afterward. In our study, most, if not all, insecticides tested no longer provided any protection after 14 days. That means most insecticides are not that useful as a “preventative” tool.

What are you trying to prove with this study? What have you learned so far? We are trying to determine, first, how often insecticides provide a return on investment by preserving yield, and second, which insect pests are most likely to be responsible when they do. We work with farmers in this study. Growers interested in evaluating these treatments on their own farms should contact me at [email protected].

What is the take-home message on spraying insecticides in soybeans so far? The best approach is to scout and use an insecticide only when justified by the pest population.

Read more about:

Insecticide

About the Author

Tom J. Bechman

Midwest Crops Editor, Farm Progress

Tom J. Bechman became the Midwest Crops editor at Farm Progress in 2024 after serving as editor of Indiana Prairie Farmer for 23 years. He joined Farm Progress in 1981 as a field editor, first writing stories to help farmers adjust to a difficult harvest after a tough weather year. His goal today is the same — writing stories that help farmers adjust to a changing environment in a profitable manner.

Bechman knows about Indiana agriculture because he grew up on a small dairy farm and worked with young farmers as a vocational agriculture teacher and FFA advisor before joining Farm Progress. He works closely with Purdue University specialists, Indiana Farm Bureau and commodity groups to cover cutting-edge issues affecting farmers. He specializes in writing crop stories with a focus on obtaining the highest and most economical yields possible.

Tom and his wife, Carla, have four children: Allison, Ashley, Daniel and Kayla, plus eight grandchildren. They raise produce for the food pantry and house 4-H animals for the grandkids on their small acreage near Franklin, Ind.

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