White mold could be a problem again in 2010

By Matt Reese

Chances are looking all too good for another bout with white mold this year in Ohio soybeans.

Anne Dorrance, Ohio State University Extension plant pathologist, said once the white mold producing material (Sclerotinia) is in a field, it will be there.

“Sclerotinia white mold, also known as Sclerotinia stem rot has a very interesting disease cycle. The inoculum comes from very small fruiting bodies called apothecia that form from the sclerotia,” Dorrance said. “This was a bit of a surprise as the 2 weeks prior to this were dry, but rains did fall 3 to 4 days prior, the night time temperatures hit below 70 a couple of nights and more importantly — there was still heavy dew on the plants at noon.”

Because of the potential for problems this year it will be important to carefully scout fields with a history of white mold. Fields that have formed a dense canopy prior to flowering and experience consistent moisture and a few cool nights are at the highest risk for this disease, Dorrance said.

“These fields are those that always have some white mold in them — this disease does not occur in every field across the state. For those historically positive fields, this is a year to watch,” Dorrance said.

To treat white mold, the fungicide Topsin M needs to be applied at the R1-R2 growth stage. And, with Ohio soybeans at just about every growth stage from V1 to R4, Dorrance points out that this could be a challenging undertaking.

“All fungicide applications work best when applied prior to arrival of fungal spores, as protectants on the leaves or stems depending on the disease in question,” she said. “Whenever you apply a fungicide, always leave a control strip or two (not the edge of the field) to evaluate if the treatment worked.”

This Sclerotinia found in the soil of some fields can develop into white mold with the right conditions. Photo by Ohio State University Extension.

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