White mold, caused by the fungus Sclerotinia sclerotiorum, is a serious disease problem on a number of different plant species. In Iowa, the best known host is soybean. However, many ornamental plants are also susceptible to white mold. The disease has recently been found on chrysanthemum and salvia samples submitted to the Plant Disease Clinic.
The disease is usually first noticed when the plant wilts. A fluffy white mold forms on the stem. Eventually, hard black sclerotia about the size of a sunflower seed can be found on the inside of stems and on the stem surface.
Sanitation, or removal of infected plants, is the primary means of disease control. Sclerotia that are allowed to fall to the ground can serve as a source of disease inoculum in following years. Proper spacing is also a management tool. Crowded plants maintain a moist environment at the soil line, favoring infection. Fungicide applications are an option, but are only useful when combined with sanitation measures.
The biology of the fungus is described in Pm-1731 Soybean White Mold.
This article originally appeared in the June 30, 2000 issue, p. 83.