NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

February 17, 2000

Recordkeeping, Crop Rotation Keys to Controlling White Mold Disease

Sclerotinia (white mold) head rot was common on sunflower across a wide area of eastern North Dakota in 1999. Likewise, white mold on dry beans and Sclerotinia stem rot of canola were common. Producers who had white mold problems in 1999 will need to be particularly diligent in key areas of their management practices this year--and for several years--because of the persistent nature of this disease, says a specialist with the North Dakota State University Extension Service.

"Producers need to keep records of fields that had high levels of Sclerotinia, as high populations of this fungus can survive for four or more years in the soil," says Art Lamey, extension plant pathologist at NDSU. "When planning rotations, keep in mind that sunflower may be infected through the roots any time it is planted in an infested field, so avoiding infested fields is essential for sunflower."

In addition to sunflower, producers with white mold concerns should avoid planting other highly susceptible crops such as dry beans and canola in fields that had severe Sclerotinia within the past three years, Lamey explains. Sclerotinia head rot of sunflower, stem rot of canola and white mold in dry beans develop when wet weather occurs before and at flowering, resulting in infection from airborne spores. Infections from airborne spores are minimal in dry weather.

Broadleaf crops that can be planted in Sclerotinia-infested fields include flax, buckwheat and semi-leafless field peas, Lamey says. These crops are not likely to be severely damaged, nor will they contribute to a buildup or maintenance of Sclerotinia in the soil.

In addition, Lamey offers the following considerations for managing white mold:

• Small grains and corn are immune to white mold.
• Many broadleaf weeds are Sclerotinia hosts, so controlling these weeds is essential even when growing immune crops.
• Deep burial of sclerotia (the hard, black Sclerotinia bodies which resemble rat droppings) can prevent release of airborne spores--as long as shallow tillage occurs in subsequent years so that the sclerotia are not returned to the soil surface.
• Sclerotia overwintering in sunflower stalks are degraded by parasites; bury these stalks in the spring.
• The fungicides Benlate and Topsin M can be used at early bloom on dry beans to suppress white mold if rainfall totaling at least 3 to 5 inches has occurred during the two- to three-week period prior to bloom, the crop canopy is thick and more rain is predicted.
• Quadris fungicide can be used at early flowering on canola if wet weather has preceded flowering and the crop canopy is thick.

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Source: Art Lamey (701) 231-7056
Editor: Dean Hulse (701) 231-6136