WOOSTER, Ohio -- It's never too early to think about soybean diseases.
Anne Dorrance, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center, said that growers can begin preparing for a number of crop diseases -- from old hats to those not normally found in Ohio.
"As far as diseases that occur every year in the state, the most important are caused by the pathogens Phytophthora sojae and soybean cyst nematode," said Dorrance, who also holds a partial appointment with Ohio State University Extension. "Both Phytophthora root and stem rot and SCN are effectively managed by knowing what's in your field and by choosing resistant varieties."
Phytophthora is the No. 1 disease of Ohio soybeans, with yield reductions ranging from five to 30 bushels per acre depending on variety, and potential economic losses as high as $120 million in any given year. Driven by saturated conditions, especially in poorly drained soils, Phytophthora can cause rapid yellowing, wilting, and root rot of young plants, and leaf yellowing and wilting of older highly susceptible plants.
"Seed treatments, careful variety selection and well-drained soils are the most effective means of managing Phytophthora," said Dorrance.
Soybean cyst nematode follows closely behind Phytophthora in its ability to limit yields. Soybean cyst nematodes feed on the roots of young plants, which prevents the roots from taking up vital nutrients.
Growers generally shrug off SCN (only 3 percent of Ohio's fields have been tested, based on samples submitted to Ohio State's C. Wayne Ellett Plant and Pest Diagnostic Clinic). However, what growers don't know can hurt them, as the pest does its best work out of sight: stealing yields in such small amounts over so long a period of time that poor plant performance is blamed on other factors.
"If growers have SCN problems, or suspect SCN, how long have they been growing soybeans in that same field? Are they using a resistant variety? If so, are they still getting yield benefits?" said Dorrance. "Nematodes do adapt if growers continue using the same resistant package. Growers should go back and take a look at their records and compare previous year yields and yields of their neighbors to what they are getting now. If they are slipping, it's time to go back and figure out why."
In addition to Phytophthora and soybean cyst nematode, Dorrance is encouraging growers to pay closer attention this year to frogeye leaf spot. Frogeye, a disease uncommon in Ohio, is now beginning to show up more frequently. Last year was the first time growers suffered economic losses to frogeye, anywhere from a 10 percent to 30 percent yield loss.
"We've always thought that this pathogen would never overwinter here so we didn't need to worry about it. Well, we were wrong and during the 2005/2006 season, we had a really mild winter, and we got caught with high levels of disease," said Dorrance.
The frogeye pathogen survives in crop residue and makes its appearance in late summer, affecting leaves and sometimes spreading to stems and pods.
Growers can manage frogeye by:
• Practicing tillage to bury crop residue and reduce the amount of disease inoculum.
• Practicing crop rotation. "If you had soybeans in that field the previous year, plant a different crop this year," said Dorrance.
• Planting resistant varieties. "If a grower has to be in soybeans, just make sure he or she chooses a variety that has been documented as having good frogeye resistance," said Dorrance.
Soybean rust, also a foliar disease, is on the bottom of the list of concerns for the moment, said Dorrance.
"My worry button is not going to get hit until we get our crop in the ground and then go back to see how much rust is in the South," she said. "Then we'll begin putting out predictions of rust potential on Ohio's crop."
According to the U.S. Department of Agriculture's Pest Information Platform for Extension and Education Web site (http://www.sbrusa.net), soybean rust has been reported on kudzu in Alabama, Florida and Georgia. Last year, soybean rust was identified in 15 states, spreading as far north as Kentucky and southern Indiana.
For more information on Ohio soybean diseases and how to manage them, log on to OSU Extension's Agronomic Crops Team Web site at http://agcrops.osu.edu.