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How to Manage PestsUC Pest Management Guidelines
SYMPTOMS Under high humidity the fungus produces a mass of cottony hyphae or mycelia on the soil surface. Later, large (2-10 mm), black sclerotia (hard, dark mass of hyphae) are formed on infected plant parts. Frequently the sclerotia are found inside of dead stems. Plant tissues killed by the fungus often take on a bleached appearance. Gray mold (Botrytis cinerea) causes a similar bleaching and also has black sclerotia, but they are smaller than those of Sclerotinia; it also doesn't produce the mass of white, cottony growth that Sclerotinia does.
COMMENTS ON THE DISEASE Sclerotinia sclerotiorum does not produce conidia. Sclerotia formed by the fungus undergo a dormant period that is broken by low temperatures (optimal is 56° to 59°F) and high soil moisture. In fall and spring when temperatures are in the optimal range, the sclerotia germinate to form apothecia (saucer-shaped, dime-sized structures on stalks) that produce spores. The spores are discharged forcibly into the air and are carried by air currents. They do not directly infect healthy tissue, but if they land on injured tissue in the presence of moisture, infection occurs. Flower petals of many plants are susceptible. Foliage may become infected if there is an injury or if the tissue is senescent. If diseased tissue comes in contact with healthy tissue, the fungus can invade the healthy tissue. Infections frequently occur at the soil level because plants can be infected directly by sclerotia in the soil that germinate to produce vegetative strands (hyphae).
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UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries |
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