6 ways to combat red crown rot

LEXINGTON, Ky. — Red crown rot is a concerning, relatively new disease to the Midwest that more farmers are finding in their fields. The pathogen was found in Illinois in 2018 and Indiana in 2022.

Carl Bradley, plant pathologist at the University of Kentucky, discussed red crown rot during a webinar hosted by Pioneer.

“The first symptoms that you can see are the red discoloration on the lower stem or hypocotyl,” he said. “You can see that during the early vegetative stages, but you may not see anything else that would draw you to that area.

“Later on, when we get to the reproductive development stages of soybeans, you’re going to start seeing the leaf symptoms — that interveinal chlorosis and necrosis that can look like SDS and some of those other diseases.”

Symptoms:

• Interveinal chlorosis, or yellowing, and necrosis of the leaves.

• Reddish-colored lower stem.

• Reddish-orange, spherical perithecia.

• Root rot.

• Patchy distribution in the field.

The disease is caused by a soilborne fungus called Calonectria ilicicola. There are many ways it can spread from one field to another, including water flow, soil movement, plant debris, animals and equipment.

“We’re still learning about best management practices as this is a new disease to our area,” Bradley said. “But there are some things we know will help.”

1. Rotate crops.

“First off, crop rotation is important,” Bradley said, “not just for red crown rot, but for a lot of other diseases. This fungus can live for multiple years — so crop rotation alone will not get rid of the disease, but it will help.”

2. Manage soybean cyst nematode.

“We know from research that soybean cyst nematode can interact with red crown rot,” Bradley said. “In fields with a soybean cyst nematode infestation, red crown rot can be worse. Make sure you’re managing soybean cyst nematode and potentially other stresses to make the symptoms of red crown rot less bad.”

3. Clean equipment.

“If you know you have red crown rot in a particular field, be sure you clean that equipment in that field so you don’t move that soil and pathogen to additional fields,” Bradley said. “It will slow the field-to-field spread of the pathogen.”

4. Consider the planting date.

“The ideal soil temperature for infection is between 77 and 86 degrees,” Bradley said. “If we go out in early to late March, April — depending on where you are — you won’t have those soil temperature conditions. In Kentucky, we hit those temperatures with double-crop soybeans.”

5. Consider fungicide seed treatments.

“There are a few fungicide seed treatments with red crown rot on the label,” Bradley said. “Be sure your state is listed on the label, as it’s state by state. We’re looking at efficacy and testing these products.”

6. Avoid planting super susceptible varieties.

“We don’t have a ton of in information on this,” Bradley said. “As we do more work, we’ll know a lot more.”

Compared to healthy plants, the yield loss in fields with red crown rot can be pretty severe.

“It depends on how many of those patches and how big they are in your field before you really see it on the yield monitor,” Bradley said. “As this disease progresses, you see the losses more and more.”