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Rotate to fight white mold

Sclerotinia, or white mold, has been an issue for many soybean growers. 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 10 or more days, the sclerotia bodies will germinate and develop spores that infect the plants. It can take up to three to four 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 will wilt and later die. Pod fill will be set back and can be reduced to zero. Yield loss can be greater than 15 bushels per acre in the most severe spots of the field.

White mold infection is really an environmental problem, not a varietal one. I 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 score their varieties for white mold 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.

Hard to manage

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. Keep soybeans off ground previously planted to susceptible crops such as dry beans, sunflowers, canola or soybeans.

Spelhaug is an agronomist with Peterson Farms Seed, Harwood, N.D. Contact him at 866-481-7333, or visit www.peterson
farmsseed.com.

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MOLD HOME: Soybean leaves form a thick canopy, creating a good environment for the spread of white mold.

This article published in the December, 2010 edition of DAKOTA FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.