Weeping willows are susceptible to many types of diseases. Weeping willow diseases can present themselves in a variety of forms. Common signs of problems include discolored leaves, bark and wood. Dark brown or reddish tints can appear on the roots and leaves. When the discoloration girdles the tree it is a sure sign that the specific root disease has become serious and the tree is in danger of dying.
Diseases of the weeping willow tree can have several common symptoms. Signs of an ailing tree include leaf discoloration, girdling of the trunk by a dark colored ring or galls, twig dieback, defoliation of the canopy, cankers and bark discoloration.
The main effect of diseases that affect the weeping willow is rot. As the tree becomes more affected by the disease or a combination of diseases, weakening and decay begin to occur from the inside. Over time, parts of the tree can die, including roots; this can occur over short or long durations. If enough of the tree is affected, it can collapse upon itself or fall over from its own weight.
Diseases of the weeping willow tree can be brought about by one of three causes: bacterial infection, fungal infections or pests. Some diseases are caused by the onset of two or more other ailments occurring simultaneously. One of these diseases, willow blight, is caused from the onset of both willow scab fungus and the Physalospora miyabeana fungus at the same time, according to the University of Florida Extension. Two of these diseases are caused by bacteria: bacterial twig blight and crown gall. The remainder are caused by a fungus either arriving from the soil or in the air. Most often both bacteria and fungi enter the tree through injured sections or open wounds such as insect-bored holes, lawn equipment scarring or acts of nature.
There are eight common types of disease associated with weeping willow trees. These diseases are bacterial twig blight, cotton root rot, crown gall, cytospora canker, leaf spots, powdery mildew, rust and tarspot. Bacterial twig blight can be confused with frost damage because it infects leaves as they unfold; the common signs of this disease are brown streaks in sections of the wood. Crown gall resembles large, rough swellings on lower stems and crowns of the tree; deformation, stunting and death can occur. Weeping willows also suffer from cytospora canker similar to poplar trees; this ailment shows as discolored, sunken well-defined areas on branches and trunks. Leaf spots are small or large round spots of varying colors on leaves; signs include early leaf drop and withering. Rust is a disease known for its lemon-yellow spots on the lower surface of the leaf that later form into dark colored pustules; this disease causes defoliation from early leaf drop. Powdery mildew is a fungus on the leaf that becomes heavy during the latter half of the season and is most viable on young leaves and sprouts. Tarspot is evident by the thick, black, small (1/4-inch diameter) spots looking like tar. Cotton root rot is the most serious and lethal of the weeping willow diseases. Trees may quickly wilt and die, roots will decay and bark peels off easily when affected by this disease.
Most weeping willow diseases can be treated by pruning off infected areas and destroying the cuttings. Spraying early in the season with fungicides such as a fixed copper fungicide also helps.