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College of Food, Agricultural, and Environmental Sciences


Keep an Eye on Late-Season Soybean Diseases

August 20, 2007

WOOSTER, Ohio -- Ohio's soybean season may be winding down, but there still are numerous diseases and pests that growers are contending with.

Anne Dorrance, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center, said that growers should scout and manage these fields where needed to keep late-season soybean diseases at bay.

Some diseases that growers should pay close attention to include:

• Frogeye leaf spot -- The foliar disease, rare in Ohio, has been found in susceptible soybean fields throughout Ohio. The pathogen survives in crop residue and makes its appearance in mid to late July, affecting leaves and sometimes spreading to stems and pods. Frogeye lesions are distinct from other soybean foliar diseases in that they have a gray-silver center surrounded by a cranberry-red border. "Growers with susceptible varieties are reporting frogeye in the upper plant canopy. But only treat with fungicides if frogeye is easy to find and is spreading easily," said Dorrance, who holds a partial OSU Extension appointment. "If there is no disease in the field, don't spray. If frogeye is stuck in the lower canopy and it's not spreading to the upper canopy, it may not be economically feasible to spray, since we are so close to the end of the season. In addition, if two-spotted spider mite is present, don't spray. Fungicides will kill beneficial fungi that help keep the mites under control."

• Soybean cyst nematode -- Dry weather has favored the development of soybean cyst nematode, and growers have been reporting the pest in fields as early as the first part of July. Soybean cyst nematode damages soybeans by feeding on plant roots, robbing the plant of nutrients, and by providing wound sites for fungi to enter. The severity of crop damage and yield loss is dependent on crop rotation and the soybean variety planted.

• Sclerotinia white mold -- Driven by moisture before and during the flowering period, white mold has been reported by growers with fields that habitually experience white mold problems. White mold is identifiable by a thick white mold that covers the stems. Plants first appear wilted and then die as leaves and stems turn brown.

• Sudden death syndrome -- Sudden death syndrome, similar to brown stem rot, is always present in fields with soybean cyst nematode. "Sudden death syndrome can be managed by managing soybean cyst nematode populations," said Dorrance. Sudden death syndrome, like brown stem rot, is readily found in compacted fields and will turn upper plant leaves brown with a characteristic yellow color between the leaf veins. "With sudden death syndrome, if you cut open the tap root, it will be gray or brownish in color, but the pith or center of the stem will be white. With brown stem rot, that pith will be chocolate brown. It's important to distinguish the two diseases because they are managed differently."

• Charcoal rot -- Dry conditions favor the development of charcoal rot, which causes premature death of plants. The disease is characterized by grayish-black root and lower stem discoloration.

One disease that growers won't have to concern themselves with this year is soybean rust. According to the U.S. Department of Agriculture Pest Information Platform for Extension and Education Web site, the farthest north the disease has been identified so far is Oklahoma.

"With the weather patterns predicted over the next several weeks, it doesn't look like soybean rust will reach us. And if it does, we are so close to the end of the season that it won't have an impact on the crop," said Dorrance. "So there is low risk for infection in Ohio fields. We are out of the woods and everybody can relax."

For more information on managing soybean diseases, log on to

The soybean is Ohio's No. 1 field crop commodity, generating over $1 billion to the agricultural industry, according to the Ohio Department of Agriculture. Soybeans are grown in Ohio for a wide variety of uses -- from grain to food to renewable energy production.

Candace Pollock
Anne Dorrance