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White Mold (Sclerotinia)

Here is another problem we can expect to see in wet areas of the state. White mold is more prominent in relatively cool temperatures; nighttime temperatures of 60 degrees F may have triggered new infections for 1998.

White mold is caused by the fungus Sclerotinia. It may remain in the soil in a "resting" spore stage (sclerotium) for three to five years. These sclerotia resemble large black seeds or rabbit pellets with gray interiors. Sclerotia germinate at relatively cool temperatures; sporulation requires a period of wet weather.

Sclerotinia white mold is common on tomato, green bean, pepper, soybean, begonia, daisy, delphinium, hydrangea, marigold, pansy, and zinnia. Report on Plant Diseases No. 1008 lists many other hosts of white mold. To identify this disease, look for bleached areas on the stems and leaf axils that look almost like animal bones dried in the sun. In cool, wet weather, a fluffy mold develops on the stem. In seven to ten days, sclerotia form inside the stem or on the outer stem surface. Surface sclerotia easily fall to the ground, where they are transported by equipment, plant material, animals, and water.

There are no rescue treatments to save infected plants. Try to prevent future infection by keeping plant density low. Prune surrounding plants to increase air movement through the garden. Preventive fungicide applications may help in areas where white mold is a problem every year. Chemical options are provided in the Illinois Homeowners' Guide to Pest Management and the Illinois Commercial Landscape and Turfgrass Pest Management Handbook, 1998-1999. When white mold is a recurrent problem, rotation out of the infected area is recommended for at least three to five years.

Author: Nancy Pataky


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