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White Mold

July 30, 2003

White mold, watery soft rot, cottony rot, and Sclerotinia disease are all names for the same disease. The causal fungus is Sclerotinia sclerotiurum, S. minor, or S. trifoliorum. The fungus is favored by cool, wet weather as we have just experienced (odd to say for late July). These fungi can infect more than 370 species of plants, so the host range is wide. In Illinois, we might see this disease on vegetables such as green bean, carrots, and peas. A recent ginger sample at the Plant Clinic was infected. Also, look for the disease on aster, begonia, columbine, dahlia, delphinium, larkspur, peony, snapdragon, and other garden plants. It occurs on some woody plants as well, but that does not seem to be a problem in Illinois.

Symptoms of white mold may occur on any above- or below-ground part of the host. Youíll see the problem where plantings are dense and the soil is wet. Look for brown lesions, especially on the stems, which become covered with a fluffy, white mycelial growth (mold). This growth is very white and wispy, compared to the gray mold of Botrytis. As the disease develops, the large, black resting bodies of the fungus look much like irregular rabbit pellets growing in or on the plant tissue. When cut open, the resting bodies are black outside and white inside. As the infected plant tissue dries down, the white mycelium may dry up; but the canker will still be bleached or tan, as if it was grabbed by a very hot hand or glove.

This disease is discussed in Report on Plant Disease (RPD), no. 1008, available on U of Iís Vista Web site or in local Extension offices. Correct identification is important to disease control because the resting stage can remain in the soil for many years and cause problems on many other hosts. There is no cure for plants once they are infected. RPD 1008 lists susceptible plants.

Author: Nancy Pataky


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