The American Linden is a deciduous tree native to North America. Commonly termed the Basswood, the tree can reach mature heights up to 80 feet with a 35- to 50-foot spread. It is a water-loving tree that can tolerate short periods of flooding conditions. It is intolerant to drought conditions and becomes more susceptible to disease during these conditions.
Anthracnose leaf blight is a fungal disease that develops during periods of wet, moist weather. Linden trees that have been infected with anthracnose will develop dark colored lesions. The lesions will initially appear yellowish or tan but will darken as the disease worsens. The infected foliage will become distorted, wilt and will fall from the tree. Newly developing foliage will appear to be withering and distorted. Repeated premature defoliation will cause loss of vigor and severe dieback.
Anthracnose can be controlled with a combination of fungicidal treatments, pruning and care. Remove infected areas from the tree. The American Linden should be properly fertilized and irrigated to promote vigorous growth.
Powdery mildew is a fungal disease that requires no water for transportation. This airborne fungal disease begins as a cosmetic infection. Infected foliage will initially develop small white fungal spots. As the fungus spreads, the fungal spots begin to connect, forming a powdery white covering across the surface of the foliage. Infected foliage may also experience leaf curling. Severely infected foliage will begin to turn brown and wilt.
The American Linden may experience several bouts of early defoliation if left untreated, which will weaken the overall state of the tree. The mildew can be easily washed away with a strong stream of water. Fungicidal treatments are effective in preventing infection.
Verticillium wilt is a soil-borne fungal disease that infects the American Linden through its root system. The American Linden is mostly resistant to this disease but becomes susceptible when it is drought stressed. The infected tree will initially show symptoms such as yellowing or reddening of foliage veins, leaf curling and defoliation. Infected wood will show streaking and discoloration of its vascular tissue and the bark may begin to peel.
American Linden cannot be cured of the verticillium wilt disease. However, the symptoms and progression of the disease can be slowed. The tree must be properly irrigated and fertilized to promote vigorous growth. Prune off infected foliage and limbs.