The problem is most severe when nights are cool and humid, and days are warm and dry. Remove and destroy all infected leaves, including those on the ground. To prevent mildew or to arrest its spread, apply a fungicide once every 10 days, starting in midspring. Small red, brown or purple spots develop on upper leaf surfaces. The center of each spot eventually dries out, turns white and may fall out of the leaf.
Leaves eventually turn yellow and fall from the plant.
Spot anthracnose, a fungus disease. The fungus spreads in water. When symptoms appear, begin spraying with a fungicide once every seven days until all signs of the disease are eliminated. Do not water plants from above, since the fungus spreads in splashing water. Rosebuds fail to open and are covered with a grayish brown, fuzzy mold.