Downy mildew is a common problem in impatiens beds, especially in the humid climate of the southeastern United States. It carries easily between plants and causes yellowing, wilting and, eventually, death. There is no cure for downy mildew after it is established. Other possible causes of problems in impatiens include spider mites and a nutritional deficiency from poor soil conditions.
Downy mildew is a type of water mold that spreads through wind and water. Some varieties become integrated into the leaves of the impatiens plants and return the following year to infect new plants. This makes downy mildew extremely difficult to eradicate. Downy mildew is most common in the spring and fall months when there are regularly wet weather conditions.
Early symptoms of downy mildew include numerous yellow dots on the plant leaves, leaves with a wilted or droopy appearance, and white fuzzy spots on the underside of the leaves. As the disease progresses, the plant stops growing, loses leaves and eventually dies. Because there is no cure for downy mildew, it is usually necessary to destroy the impatiens and plant another type of plant in that area for the next year or two.
Spider mites are tiny bugs that feed on the leaves of impatiens and other common garden plants. They are difficult to see but eventually cause brown, yellow or gray speckling on the leaves. If untreated, the leaves eventually fall off, and the plant may die. Spider mite infestations are treated with insecticides.