Sclerotinia Stem Rot of Canola. Sclerotinia is not a water mold, but it is favored by saturated soils at flowering. Areas with saturated soils and canola that is flowering are at risk, especially if Sclerotinia or white mold has been a problem in the area in susceptible crops in previous years. The crops most liable to support the buildup of Sclerotinia include sunflower, dry bean, canola, crambe and soybean. Use of a fungicide on canola was discussed in last week's Crop and Pest Report.
Infections are most common when sunflower plants are young.
Systemic infections occur when heavy rains occur before sunflower emergence or shortly after emergence. The systemic infections result in stunted plants with yellowing along the main veins on the upper leaf surface and a downy white growth along the main veins on the lower leaf surface. After the systemically infected plants appear, secondary spread may occur if wet weather occurs again. Systemic infections are not significant if there is an infected plant here and there in a row, but if there are large patches of plants infected, yields will be reduced as most systemically infected plants die or do not produce seed. The secondary infections are not thought to cause any yield damage, but can cause serious concern by growers, if they see a majority of plants with secondary downy mildew and fail to distinguish between the systemic primary infections and the local secondary infections.