Steve Gauck  inspects soybean plant
STAGE GROWTH: Steve Gauck looks for blooms and pods to determine growth stage in soybeans. This plant has blooms on the uppermost nodes but no pods, indicating it is in the R2 stage.

It pays to know soybean growth stages

Soybean Watch: Identifying soybean growth stage helps determine how you can manage them best.

Do you know what stage of growth your soybean fields are in today? If you don’t, is it worth learning how to determine stages and taking a closer look?

Steve Gauck, a Beck’s sales agronomist based near Greensburg, Ind., believes being able to stage soybean growth is an important skill to have if you want to fine-tune your soybean management and decision-making skills. Several product labels for various inputs are tied to knowing stage of growth.

“It’s relatively easy to do, and it helps you track crop progress during the season,” Gauck says. “There are resources available which can help you learn how to determine soybean growth stages.”

One of those is the Purdue University Corn & Soybean Field Guide, Gauck says. There is also an app version of the guide, available for a nominal cost in your app store. It’s called Soybean Field Scout.

Gauck visits the Soybean Watch ’18 field regularly, and usually checks stage of growth during each visit. Soybean Watch ’18 is sponsored by Beck’s.

Reproductive stages
Beginning bloom is defined as the R1 stage, or the first stage of reproduction, Gauck says. According to the Purdue field guide, plants are at R1 when there is an open flower at any node on the main stem. The R2 stage is defined as the point when there is an open flower at one of the two uppermost nodes on the main stem which have at least one completely unrolled leaf.

The Soybean Watch ’18 field reached R2 in late June, Gauck notes. “Plants typically stay in this stage for a couple weeks or more,” he adds. “Even though plants are blooming, they are also still putting on vegetative growth.”

Many herbicide labels determine when application should cease based on soybean growth stage. The dicamba label for dicamba soybeans specifies a point at which the herbicide should no longer be applied.

That doesn’t mean all weeds are controlled at that point. However, applying dicamba or any other herbicide to soybeans that are past the stage of growth at which the product can be applied results in an off-label application.

“It’s one of the reasons to understand growth stages of soybeans and to anticipate how quickly they might reach certain stages,” Gauck says.

Fungicide applications
Several agronomists looking at results from various trials in the Midwest recommend that if you’re applying fungicides to soybeans, the best time is when they are in the R3 growth stage. If you wait to apply until R4 or later, you may not reap all the potential payoff from the fungicide, Gauck says.

R3 begins when small pods at least a quarter inch long develop on one of the four uppermost nodes on the main stem, Gauck says. By the time those pods reach three-fourths of an inch long, soybeans have reached the R4 stage.

Soybean development is affected by day length, but it’s also influenced somewhat by planting date and conditions during the growing season, Gauck says. With heat units accumulating quickly this season, it may explain why soybeans seem to be reaching the next growth stage faster than you might expect.

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