ISSUE 13 July 24, 2003
Weather conditions have been appropriate in recent days for development of white mold in vegetables and ornamentals (grasses are nearly the only non-hosts). This is a fungal disease caused by the ubiquitous pathogen, Sclerotinia sclerotiorum. Conditions favorable for disease development include high humidity and cool to moderately warm temperatures (40-85oF). Spent flowers, dried leaves, and weakened plant parts are most susceptible to infection; and the pathogen then continues to invade healthy, green plant parts. Infections range from barely noticeable to complete destruction of the plant.
White mold will be most apparent as bleached, sometimes shredded plant stems. White, fuzzy growth may also be visible, often close to the soil line. Small, black roundish to oval structures may be seen on the outside of the stem, or in the interior of the stem if it is cut open. These are hardy structures that provide a site for the fungus to survive winter, and are the source of new infections each year.
Management of white mold includes picking off infected or dried plant parts and removing dead plants. Thinning to increase air circulation may also help. Since this can be a perennial problem in areas where infection has occurred, rotating susceptible hosts every 3-4 years is beneficial. Plant into well-drained soils and space adequately to allow for good air circulation. See this bulletin for more details: