Phomopsis seed decay is now showing up in some soybean fields in Ohio. The disease, which causes cracked, shriveled, moldy seed, impacts yield and reduces seed quality and grade.
Anne Dorrance, an Ohio State University Extension plant pathologist, says Phomopsis seed decay or rot occurs when wet weather occurs frequently during pod fill and harvest is delayed.
According to the Ohio Agricultural Statistics Service, only 10% of Ohio's soybean crop is harvested, down from 33% this time last year. USDA's most recent crop report calls for a state average of 46 bushels per acre 10 bushels more than last year. Total Ohio production is pegged at 210.68 million bushels up 31% from 2008.
"Phomopsis is typically rare, but conditions this summer with frequent rains and now delayed harvest are the perfect environments for this soybean pathogen to take hold," says Dorrance.
Phomopsis seed rot is caused by a complex of three different fungi including Diaporthe phaseolorum var. sojae, Diaporthe phaseolorum var. caulivora, and Phomopsis longicolla. Phomopsis longicolla is the one most commonly associated with seed rot but all three can infect seed. All of these fungi overwinter on infested soybean straw in the field or may be seed-borne.
Growers are recommended to check their soybean fields before harvest for signs of the disease.
"Crack open a few pods. Affected seeds are white, chalky, shriveled and lightweight," says Dorrance. "If seed is infected, then turn up the blower. Much of the affected seed will be blown out. "
To manage Phomopsis seed rot, producers are advised to harvest seed when it reaches 13 to 16% moisture, regardless of stem conditions; rotate with wheat or corn to reduce fungal survival on soybean straw residue; practice minimal tillage; and select varieties with high levels of resistance.
For more information, refer to OSU Extension's fact sheet, "Phomopsis Seed Rot of Soybeans," (AC-36-09) at ohioline.osu.edu/ac-fact/pdf/AC_36_09.pdf.