This is a fungal disease that we see only in very wet years.
Many ornamental crops could be affected, including begonia,
daisy, delphinium, hydrangea, marigold, pansy, and zinnia.
Vegetable crops commonly affected are tomato, green bean,
White mold is caused by Sclerotinia,a fungus that
thrives in cool, wet weather. Due to near ideal conditions
in many parts of Illinois, this disease should be expected.
The fungus remains in a resting state (sclerotia) in the
soil for many years. With ideal conditions, fruiting bodies
(apothecia) form and spores are released into the air. A
period of wet weather is then required for infection to
follow the spore release. It is easy to understand why the
alternating wet and dry periods experienced in some parts of
the state have been ideal for Sclerotinia white mold.
Symptoms of white mold are bleached areas on the stems
and at the leaf axils. These areas appear almost like animal
bones dried in the sun. In cool, wet weather, a white fluffy
mold develops on the bleached areas. Within seven to ten
days, sclerotia form: large, black structures, almost like
rabbit droppings, found inside the stem (and occasionally on
the outside as well).
Control options for this disease are limited. The home
grower can try to keep plant density low so that air
movement helps dry out plants sooner. There are no rescue
treatments available for commercial use. Fungicide
applications may help on a preventive basis in areas where
this is a problem every year. For chemical options, consult
the 1997 Illinois Commercial Turf and Ornamental Pest