Record keeping, 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.

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. 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. 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. These crops are not likely to be severely damaged, nor will they contribute to a buildup or maintenance of Sclerotinia in the soil.

Facts to consider:

1. Small grains and corn are immune to white mold.

2. Many broadleaf weeds are Sclerotinia hosts, so controlling these weeds is essential even when growing immune crops.

3. 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.

4. Sclerotia overwintering in sunflower stalks are degraded by parasites; bury these stalks in the spring.