White mold in soybeans

White mold was found more in 2019 than in years past. Weather conditions also ushered in sudden death syndrome.

The topsy-turvy 2019 growing season ushered in more disease than usual, but relatively few fields were overcome, agronomists say.

Rains that kept fields unplanted through late spring, followed by sporadic downpours throughout the growing season, made conditions favorable for unfavorable pathogens. Some disease pressure was found in areas that normally see little.

White mold was one disease farmers saw more than usual this year.

“White mold has been more prevalent in years with cool, damp conditions, especially around the flowering state of soybeans — R1 and R2,” said Kevin Scholl of Syngenta. “It overwinters in the soil and can overwinter for many years.”

Pat Holloway, an agronomist with Beck’s Hybrids who works in southwest Iowa, also saw more than usual.

“We did get white mold farther south in Iowa than what is normal,” Holloway said. “Typically, you see white mold in northern Iowa, Minnesota and the Great Lakes area. We had it 100 miles farther south than where you typically would think it would be a problem.”

Glen Hartman of USDA’s Agricultural Research Service also said white mold was more of a problem this year than in past years. Delayed planting may have reduced the impact of some disease, however.

“It just depends on where you are,” Hartman said. “There has been more white mold, and also more reports of cyst nematode. Weather and environment plays such a role in this. It may be that late planting may have offset some of the diseases because they didn’t start earlier than they normally would have. A lot of the beans were grown in warmer temperatures, especially the late ones, which is almost everything this year.”

Scholl, who is based in Illinois, said white mold is more likely to develop in fields of continual soybeans. Wider rows and application of fungicides can address the problem.

“If you’re in a rotation with more corn than beans, risk of infection is less,” he said. “It’s basically when the flower starts to senesce. The spore gets on the flower and infects the soybean plant. Growers will try to mitigate this by planting varieties with a little more tolerance.

“Wider soybean rows rather than narrow soybean rows to get more air in that canopy to dry things out a little bit better. Then fungicide, like one we just came out with — Miravis Neo — can be applied at that flower stage to help mitigate the problem. We can suppress it during that time frame.”

Holloway also said tar spot, another disease that is popping up in different areas, made its presence known this year.

“This is the first year that tar spot has made it out to our neck of the woods,” Holloway said. “It didn’t really have an impact this growing season, but it’s something we’re going to have to watch each year now. As an industry we don’t have a good handle how it’s going to take off in our environment.”

Tar spot has been a problem in the U.S. for only a few years. It was found in northern Illinois and southern Wisconsin in 2013.

“This year they found it virtually all the way across Iowa,” Holloway said.

Hartman, who is stationed at the University of Illinois, pointed out that diseases — like weeds, insects and other crop foes — are perpetual adapters.

“Diseases that we don’t normally see seem to be more prevalent,” he said. “Bacterial pustules, for example, shouldn’t be around. But because of rapid cycling, there is the potential for more seasons.”

Holloway pointed out that sudden death syndrome also popped up in some fields, though it did not establish itself as a major threat.

“We got some along an area where we got a little more rain in late July,” he said. “It needs a couple of things to happen, such as cool, wet planting and other conditions in spring.”

He added that conditions were actually favorable for limiting some disease pressure.

“In beans we did have a little more disease than we’ve seen over the past few years,” he said. “On corn, probably a little less.”

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Nat Williams is Southern Illinois field editor, writing for Illinois Farmer Today, Iowa Farmer Today and Missouri Farmer Today.