The following is more information on botrytis blight (gray mold) in the landscape.
As the weather cools and more dew forms in the evenings, conditions become ideal for the development of Botrytis blight or gray mold. To reduce this fuzzy, gray fungus, keep rose gardens and flowers beds dead-headed and spray with Daconil or Fungonil (chlorothalonil), Cleary's 3336 (thiophanatemethyl) or other labeled fungicide. Other fungicides for commercial use include Chipco 26019 (iprodione) and Decree (fenheximide) or other labeled fungicides. Often the fungus causes a stem canker when infected flowers fall into the plant canopy. Black or caramel-colored, sunken and elongated lesions, with a definite outline, frequently appear on succulent stems or stalks of such ornamentals as begonia, geranium, annual vinca, peony, rose, snapdragon and many other annuals and perennials. Infection also may spread through the stem causing it to be weakened, girdled, and collapsed at the point of infection followed by wilting of the foliage above the lesion.
Information from Bob Mulrooney, extension plant pathologist, UD.