Black rot can also be a problem in storage. Under certain conditions, the fungus also can cause a leaf blight, which is characterized by dark brown lesions along the leaf margins. The fungus is favored by sprinkler irrigation or rainy weather and high temperatures, which may predispose tissue to infection. Alternaria radicina is seedborne and may be spread on carrot seed. It also survives in carrot debris and in the soil for several years.
Black rot is important only in certain areas or regions in California.
It is common in coastal mountain valleys, e.g., the Cuyama Valley. Furrow rather than sprinkler irrigation may reduce disease development. Crop rotation is highly recommended to prevent buildup of the fungus in the soil. Deep tillage may provide some control by burying inoculum of the fungus away from the carrot crown. Foliar applications of fungicides to control black rot are marginally effective.