WOOSTER, Ohio — Excessive rain during flowering and right after planting, coupled with cool nights, have caused an increase in some late season soybean diseases in many Ohio fields.
The inclement weather during these two key time periods in soybeans have made the plants really vulnerable to disease this year, said Anne Dorrance, an Ohio State University Extension plant pathologist.
Dorrance, who has led soybean disease research and outreach efforts in Ohio, said now is the time growers should be scouting their fields to know what diseases may be impacting their soybean plants in order to know how to manage the fields to prevent similar occurrences next season.
“We’re seeing a lot of late season disease symptoms across the state,” Dorrance said. “While many of these diseases will spread, they are manageable.
“The key is to know where the pockets of diseases are. Once you know what pathogens are in your field, then you can make better choices in variety selection and crop rotation, which are two key management elements.”
For example, Dorrance said, the occurrence of downy mildew in soybeans is higher than normal this year due to highly susceptible varieties and the heavy dews and cool nights the region has experienced in recent weeks.
Because this is occurring so late in the season, the impact on yields is thought to be minimal, she said, noting that there is no data available related to how well any management fungicides would work.
“The conditions could not be more perfect for this disease,” she said.
“Downy mildew can infect seeds and if favorable conditions continue, the fungus can infect the pods and grow over the seed.”
The problem for soybean growers is that once a disease or organism is found in the soybean fields, it is there to stay, Dorrance said.
“Growers can manage disease through crop rotations, because many of these pathogens can live in soybean residue, so when we plant other crops like wheat and corn, most of the inoculum from those pathogens are decreased,” she said. For example, Dorrance said soybean cyst nematode populations can be reduced by approximately 50 percent for every year growers rotate their crops.
Another management option is to plant resistant varieties.