Look for these soybean diseases and maladies in 2021

White mold, sudden death syndrome, and soybean cyst nematode always loom in the background.

If there was an area where farmers caught a break in 2020, it was in crop diseases. 

White mold, particularly, slams Upper Midwest soybean farmers, such as in 2019. In 2020, though, that wasn’t the case. 

Still, don’t count this fungal disease out for 2021 and beyond, as it remains in soils for years. White mold flares up in years of rain, cool temperatures, high relative humidity, and moist soils.

“White mold has become a big yield-robbing disease for the last seven to eight years,” says Harmon Wilts, DeKalb/Asgrow technical agronomist.

White mold management requires a three-pronged strategy of: 

  • Variety selection. Some varieties tolerate white mold better than others, says Wilts.
  • Cutting plant populations in suspect areas. For example, farmers may want to slice a 150,000-plant-per-acre planting population down to 110,000 to 120,000 plants per acre in field areas prone to white mold. “This gets more air movement flowing through the beans,” Wilts says.
  • Fungicides. “There are some fungicides that do a good job of targeting white mold,” he says. Timing is key, as fungicides should be applied at the R1 (beginning bloom) stage, he says. 

If white mold pressure is overwhelming on a field, growing corn for a few years is another option, Wilts adds.  

Multiple Maladies

Soybean farmers should also be aware of sudden death syndrome (SDS), says Wilts. SDS symptoms often surface in August. True to its name, soybeans suddenly sport crinkly and chlorotic leaves.

Still, SDS is rooted in what happens months earlier, when the soilborne fungus Fusarium solani infects roots as early as one week after crop emergence in cool and wet soils. The infections that key Fusarium root rot can produce the toxins that later spur chlorotic and crinkled leaves.

SDS has been working its way northward in the last several years. 

“I don’t want to force the panic button yet, but we need to be selecting varieties that have a good score for SDS,” says Wilts. 

As always, soybean cyst nematode (SCN) continues to plague soybean farmers. SCN-resistant varieties exist; around 95% of them are steeped in the PI 88788 source of resistance. In some cases, SCN is resisting this resistance source.

“I encourage growers to sample their fields to see if they are keeping their (SCN) numbers low,” says Wilts.  Sampling can give farmers a base on which to base their SCN management strategy. Other resistance sources—such as those derived from the Peking source of resistance—do exist for farmers to use in an SCN-resistance strategy, he adds. 

High Yielding Potential with Defensive Traits

There’s always the concern that loading a soybean variety up with defensive traits can curb yield potential. That’s changing, though. 

“Breeders have done a great job of breeding for high-yield potential with defensive traits,” says Wilts. “With all the soybean issues we now have to deal with, we need a defensive bean that still has high yield potential. There are not many varieties that just have pure yield potential with no defensive traits.” 

That’s crucial in areas like west-central Minnesota, where soybean farmers face multiple maladies. 

“We make sure that we have beans that have a good iron chlorosis score with SCN resistance and tolerance to white mold,” he says. “The breeders have a tough job to bring all that together into one. But if we are going to continue to grow soybeans, that is what we need to do.” 

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