Causal Agent
Sclerotinia sclerotiorum
Distribution
Worldwide, except in the warmest areas of the tropics
Symptoms
In moist weather, stem infections spread rapidly downward to decay the roots and expand upward wilting leaves, resulting in plant collapse. A white, cottony growth and black, seed-sized sclerotia may be visible on or embedded in the affected tissues. When dry weather follows infection, brown cankers form on stems without progressing further. This disease may also cause losses during storage and transportation.
Conditions for Disease Development
Sclerotia of this fungus are long-lived, allowing it to persist in soil for many years. Disease development is generally favored by abundant soil moisture and temperatures ranging from 10-25°C (50-77°F). Sclerotia that come in contact with the stem or foliage may directly infect host tissue. However, the ascospores of Sclerotinia sclerotiorum require a supply of nutrients to infect. Pollen and flower parts from the host crop or adjacent weeds, such as common ragweed (Ambrosia artemisiifolia), serve as a nutrient source and permit the fungus to develop specialized structures which then penetrate the crucifer host. Crucifers, especially cabbage, that come in contact with colonized plant tissue may then become infected.
Control
Implement good sanitation practices and long rotations to non-host crops. Cultivate to help promote good soil drainage. Flood fields for a long period of time during warm weather to destroy sclerotia. Manage weeds and apply fungicide sprays to control this disease.
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