A mild winter in the South set the stage for some soybean fields to be at more risk for diseases this growing season. But, in Kentucky, that soybean disease risk is low.
"I am sure that some parts of the country probably do have an increased disease risk as a result of the mild winter, but I do not believe Kentucky is among them. … This may be a good year to consider leaving the fungicide sprayer in the barn," said Don Hershman, University of Kentucky Extension plant pathologist.
Foliar, pod and stem soybean fungal diseases are mostly controlled by resistant varieties, particularly MG 4 varieties. Not planting full-season crops early or planting late-season double crop, limited-sporadic rainfall and high temperatures during the summer months, and timely harvest can also keep these diseases at bay.
The need for a targeted, foliar fungicide to limit small yield loses is typically done in environments like river-bottoms, fields prone to extended periods of dew or fog or continuous soybean fields. Early maturing varieties, mainly group 3, are often impacted by damaging levels of FPS diseases if planted early, he said.
Kentucky did have a very mild winter, which can herald disease pressure, and high-riding soybean prices can tempt growers to protect the crop.
If anything the mild weather likely aided residue breakdown, reducing fungal survival in weed and crop residue due to increased microbial activity. Early planting may have been more common this year, but the higher-than-normal temperatures and limited rainfall in April to early-May likely reduced diseases normally associated with early planting, he said. Though mild, the Kentucky winter was cold enough to freeze out the soybean rust.
"The mild winter may have increased the risk of insect-vectored virus diseases, such as bean pod mottle virus and soybean mosaic virus," he said. "However, these viruses are not controlled by foliar fungicides."
The Kentucky soybean crop is very drought stressed now. Yields will be seriously hurt by drought if relief doesn't come soon. Charcoal rot and soybean cyst nematode may bring yields lower, too, he said.
Strobilurin-based fungicides are reported to help drought-stressed plants. "(But) it is my experience that stress tolerance benefits are simply overwhelmed when soil moisture is limiting for an extended period of time," he said.
Unless July and August turn wet, he said, it will be difficult to recover the costs associated with a soybean fungicide application this season in Kentucky.