Farm Progress

Soybean prices make soybeans following soybeans very appealing, but what about the yield penalty? Here’s what to expect and steps for combating yield loss.

Jill Loehr, Associate Editor, Prairie Farmer

December 22, 2017

3 Min Read
KEY TO SUCCESS: “Variety selection is critical for managing soybean diseases and achieving high yields,” says Jamie Long, a sales agronomist with Burrus Seed. Using precaution against soybean cyst nematodes is crucial for soybeans following soybeans.

Soybean prices look pretty good right now, right? Jamie Long, a sales agronomist with Burrus Seed, says farmers are asking a lot of questions about soybeans following soybeans for the 2018 growing season. The bad news? Emerson Nafziger, University of Illinois Extension agronomist, says farmers should anticipate a 5% to 8% yield penalty in soybeans following soybeans.

“That expectation is based on a number of years of research comparing soybean following soybean with soybean following corn,” he says.

Long believes farmers can minimize yield loss by incorporating several best management practices. Here are five continuous soybeans considerations:

1. Choose fields wisely. Stressed soybeans are more susceptible to disease issues, like root rot, so avoid low-lying fields or fields with poor drainage. Fields with known disease pressure or soybean cyst nematodes are not ideal.

“SCN is the one to watch,” Nafziger says, adding that farmers who haven’t tested soils for nematodes might want to do so before planting. Sampling in the fall or following noticeable damage, such as yellow patches in a field or cysts on roots, is ideal, but samples can be pulled before a hard freeze or in the spring. For more on nematode soil sampling, read this U of I Extension report.

2. Be picky during variety selection. “Variety selection is critical for managing soybean diseases and achieving high yields,” Long says. Use your seed company’s disease ratings to find varieties with excellent resistance to SCN, sudden death syndrome, brown stem rot, white mold and phytophthora. Remember, SCN is the top concern. Nafziger says other soybean diseases will not be worse following soybeans.

Long recommends rotating sources of SCN resistance, if possible, to reduce selection pressure. Avoid complications from late-season diseases like white mold and stem canker by planting an earlier-maturing variety.

3. Prepare your weed control plan now. What weed escapes did you have last year? Marestail? Waterhemp? Palmer amaranth? “If weeds in the soybean field went to seed this year, expect to deal with even more of those weeds in 2018,” Long says, and adds that you should plan weed control according to your problems weeds.

“Waterhemp is almost guaranteed to be glyphosate-resistant and possibly PPO-resistant,” he says. “In order to combat this weed in 2018, use an alternate soybean technology like LibertyLink, Roundup Ready 2 Xtend or Enlist E3 — if approved for 2018.” Work with your chemical representative to determine the best soil residual herbicide for your target weeds and to ensure you have multiple effective modes of action to control resistant weeds.

4. Double-check available nutrients. Multiple years of soybeans will remove nutrients, including potassium and phosphorus. Use soil tests and the updated P and K removal values as your guide.

5. Be ready for pests. Scouting is essential, Long says. “The buildup of disease inoculum and insect numbers can be yield-robbing in continuous soybeans,” she explains, adding that seed treatments such as Ilevo offer early-season protection against SDS and SCN.

“For late-season protection from foliar diseases and insects, consider a fungicide and insecticide application at the R3 growth stage,” she says. “For white mold concerns, consider lowering planting population and applying a fungicide at the R1 growth stage.”

What about tillage? Nafziger says continuous soybean yields in no-till and tilled fields are about the same. “Unless there is some good reason to till, I think the best policy for continuous soybeans will be no-till,” he says. “No-till over the winter, for sure.”

About the Author(s)

Jill Loehr

Associate Editor, Prairie Farmer, Loehr

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