Linden or basswood trees are susceptible to a variety of problems including bacterial and fungal diseases. The severity of linden infections vary from cosmetic damage to tree death depending upon the type of fungus.
Several different kinds of fungi cause anthracnose, a leaf disease, in linden trees. Fumago vagans causes sooty mold, while the Uncinula necator fungus causes powdery mildew. The Xylella fastidiosa bacterium causes bacterial leaf scorch.
Linden trees with anthracnose have brown spots with black margins along the leaf veins. They may also lose their leaves early or experience bud, leaf or twig dieback. Sooty mold is usually associated with the honeydew extruded by insect pests such as aphids or scale, according to the North Carolina Cooperative Extension. Sooty mold spores stick to the honeydew and colonize the foliage, interfering with photosynthesis. Powdery mildew is characterized by a powdery white fungal growth on the foliage, while the pathogen that bacterial leaf scorch blocks the water flow to the leaves, causing wilt and eventual plant death.
According to the University of Guelph, anthracnose infections overwinter on diseased linden tree leaves on the ground and create new infections in the spring. Raking and destroying infected leaves and pruning out infected twigs helps prevent the spread of anthracnose. Sooty mold is treated by addressing the insect problem; horticultural oils and chemical sprays are useful in eradicating insect populations. Powdery mildew is prevented by removing and destroying infected plant matter and by applying a fungicide at regular intervals during the growing season. There is no cure for bacterial leaf scorch; cultural practices such as pruning and watering help extend the tree's life span.