White Mold Scores Often Misleading

Sclerotinia, or white mold, has been an issue for many soybean growers these past years. Sclerotinia can be a problem — particularly during times of wet weather — when soybean plants become infected prior to and during the flowering period.

The sclerotia bodies from previous years can survive in the soil for over five seasons. If the surface of the soil stays wet for ten or more days, the sclerotia bodies will germinate and develop spores that infect the plants. It can take up to 3-4 weeks after infection for symptoms to show. Gray or white lesions will form on the stems and leaves above the infection point, and the plant wilts and later dies. Pod fill will be set back and can be reduced to zero. Yield loss can be greater than 15 bu/acre in the most severe spots of the field.

White mold infection is really an environmental problem, not a varietal one. We do not score our varieties for white mold tolerance due to the unpredictability of this disease, and the dependence of the disease’s presence on planting date. And I’ll be bold and say that companies that do are only guessing. While there are varietal differences in disease response, most years, even the most susceptible are not affected and even the best can be hit hard under the right conditions. It really comes down to flowering date as to when the soybean will be infected, and flowering date is affected by maturity and planting date as well. In 2009, varieties in the 0.5-0.7 maturities had more white mold symptoms. This past year the varieties in the 0.8-1.1 range had more issues. Nice lush growth and wet weather also affected the soybeans this year leading to more severity in some areas.

White mold is a hard disease to manage and plan for. There are really no good fungicides that provide prevention or complete control of it either. Wider row spacing can help but in years of lush soybean growth, similar to this year, it really has no effect. Planting a soybean that is not as bushy can help.

So what can you do? Crop rotation is the best tool. And keep your soybeans off ground previously planted to susceptible crops such as dry beans, sunflowers, canola, or soybeans.