What to Watch for With Second-Year Soybeans

Much has been written about best management practices for planting corn consecutive years. Fewer farmers consider growing second-year soybeans, but the idea may have more appeal in 2017 than in prior years, considering current commodity prices.

Fields planted to soybeans multiple years in a row will find themselves under certain specific pressures. Here’s what to watch for.

“Producers considering this practice can expect a 5% yield loss compared to soybeans planted after corn due to the rotation effect,” reports Michigan State University Extension specialist Mike Staton in one of the university’s recent newsletters. “However, plant stress caused by environmental conditions, diseases or insects can easily increase yield losses to 20% or more.”

The first line of defense is variety selection, he says. This is especially true of fields that have a history of white mold, sudden death syndrome (SDS) or soybean cyst nematodes (SCN). Select varieties that have the highest level of resistance possible for your specific problems, Staton suggests.

“These are soil-borne pathogens having the potential to cause large yield losses in the 2017 crop, as well as future soybean crops,” he says.

Mike Meyer, a field development manager with DuPont Crop Protection, says just as variety selection is crucial, so is field selection in many instances. Avoid poorly drained fields, for example – they likely have the deck stacked against them already in terms of higher disease levels.

Knowing other aspects of the field’s history is also helpful, Meyer says.

“Did you have weed escapes last year, for example?” he says. “It’s highly likely you’ll have difficult-to-manage pockets of weeds the next year. Use products with multiple modes of actions and look for good weed kill up to canopy closure.”

The same is true of disease, Staton says. Planting into a field that has a history of white mold pressure should prompt several actions, he says, including tilling at least 2” deep, reducing planting rates, planting in wide rows, and selecting foliar fungicides wisely.

These field should be scouted early and often, Meyer adds. White mold is a disease that shows up prominently later in the season, but the infection is already active around the R1 stage. As the disease progresses, it becomes more obvious – but the damage is done at that point.

“Once you get to that point, there’s nothing to prevent it,” he says. “We can’t turn brown tissue green again. We need to be preventive about managing white mold, not reactive.”

One area that might not tax second-year soybeans is insect pressures, Staton says. Farmers should still scout all fields for bean leaf beetles and soybean aphids, he adds.

As for fertility needs, Staton says not to skimp on potassium, which contributes to disease resistance. Also, potassium-deficient soybean plants are more attractive to soybean aphids, he says.

Bottom line – consider all the risks and make sure the benefits exceed those risks, Staton recommends.

“Changing your crop rotation, especially shortening it, is an important decision, as it will have long-term effects on pest populations and soil quality,” he says.


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