soybean plant likely infected with brown leaf spot

A soybean plant likely infected with brown leaf spot grows in a field in Franklin County. There have been relatively few reports of widespread disease and insect pressure across the state, though sudden death syndrome has infected some plants and red crown rot has been identified.

Some farmers in Illinois are seeing a disease they don’t see often and a relatively new one in 2020.

Sudden death syndrome, which gets its name from the way it kills soybean pods and even entire plants, has been present in many fields, though widespread damage hasn’t been reported.

Red crown rot has also been found in soybeans this year.

“For the most part, the biggest issue we’ve been seeing in soybeans is there’s been a lot of SDS coming in soybeans planted in April,” said Ben Wiegmann, an agronomist with Beck’s Hybrids. “We went through some cool, wet conditions and many farmers are having to deal with it, regardless whether they had seed treatment on them.”

Presence of the disease seems to vary from variety to variety.

“I would say it’s very variety specific,” Wiegmann said. “Some have natural tolerance.”

Red crown rot is a newer phenomenon.

“I haven’t seen it thus far in southern Illinois but I know it’s been popping up more in western Illinois,” Wiegmann said.

Jay Nelson, who farms in Reynolds, near the Quad Cities, has also heard reports of red crown rot, though he isn’t aware of major problems in his area. SDS has been more concerning.

“There is definitely some around,” Nelson said. “It’s hit or miss. For the conditions we had in the spring and the stress on the backside, I’m surprised we don’t have more of it.”

Red crown rot has been around for just a couple of years and has the potential to be troublesome, according to Chelsea Harbach, a University of Illinois Extension educator.

“Red crown rot was found for the first time a couple of years ago in Pike County,” she said. “We don’t know yet how prominent it is.”

The disease causes foliar symptoms similar to sudden death syndrome or brown stem rot, Harbach said. Control is complicated because of the way the pathogen is transmitted.

“You can end up with plants that are completely defoliated,” she said. “It is a soil-borne pathogen. It’s not spread by spores, but on equipment, contaminated soil particles and those kinds of things.

“Once in the soil, it’s a lot more difficult to manage soil diseases. With soil-borne diseases you’re relying on resistance from the cultivar. With others, though resistance is also important, you have opportunity to spray fungicides. It could be pretty serious if it spreads to enough fields. Like SDS, it occurs more in patches so won’t devastate whole fields. But it could have a serious impact on patches where it does occur.

Jim Herndon, who farms in McDonough County, has not seen or heard of outbreaks of SDS or other diseases.

“I don’t see anything in the beans,” he said. “No sudden death around here. We had some Japanese beetles early, but they didn’t do anything.”

He expects harvest to begin near the end of the month.

“We had 10 days of heat that really brought the corn on, and we got about an inch of rain, so we’re in good shape,” he said.

Nelson said that he has had to deal with some disease pressure, but nothing dramatic.

“We’ve had a lot of gray leaf spot early on,” he said. “It’s still around, but it didn’t progress as much as we thought it would. There is a lot of anthracnose, so stalk quality isn’t as good as it could be because of that.”

He has also heard about physoderma in the region.

“There’s a decent amount of that around,” he said. “That’s posing some issues on stalk quality.”

Harbach had feared SDS would be a bigger problem when its presence became known early in the growing season.

“I honestly thought it might get pretty bad there for a while,” she said. “It came on after pod set and we were forecast to have cooler, wet weather. But it wasn’t as wet. There is obviously some out there, but it’s not as bad as it could be if we had gotten more rain.”

She added that she has received relatively few reports of serious problems with insects.

“I’ve heard of some fields with rootworm problem, but in most cases those fields are continuous corn and that will increase the likelihood of having a corn rootworm problem,” Harbach said.

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