Diseases of the willow tree (Salix spp.) include disorders caused by fungal infections and improper environmental conditions. For prevention of disease, keep trees vigorous through proper care, including exposure to full sunlight to light shade and moist soil; avoid drought-like conditions. Additionally, for newer trees, prune branches for successful formation of sturdy wood and a strong trunk.
Shoot and Bud Death
Shoot and bud death is a disease that affects willow trees when temperatures drop too severely during the winter season or during frosts. This problem is also prevalent just after long stretches of warmer temperatures followed by an immediate drop into freezing temperatures. Symptoms appear during spring when flowers and leaves fail to emerge from the tree, and when they do emerge, new growth springs from old branch parts instead of the appropriate newer areas of the branch. Both shoots and buds may suffer extreme injury or death. Since buds are more tender than leaves, buds may suffer while leaves remain healthy. For control, choose hardy willow varieties and cease irrigation when autumn nears. Additionally, choose not to apply nitrogen fertilizer to grass beneath willow tree canopies during summer and autumn, as directed by North Dakota State University Agriculture.
Willow tree diseases include canker caused by the fungus called Cytospora chrysosperma. On willow trees, this fungal disease causes shoot death as well as the decline and eventual death of branches where areas on the surface or beneath bark are killed due to infection. The infected area, referred to as a canker, leads to decay of plant tissue. Maintaining a vigorous tree is key to avoiding canker infections, as stressed trees are more vulnerable to attack. Stress is often caused by improper care or drought. For control of cankers in willow trees, prune diseased tree parts, irrigate the land surrounding your tree during drier periods and make sure soil is well-drained for prevention of standing water, as suggested by North Dakota State University Agriculture. No chemical control method is recommended for canker disease of willow trees.
Heart rot is a willow tree disease caused most often by the fungus Trametes trogii. Fungus invades willow trees through any openings that bear raw wood, such as breaks or wounds; once the fungus is inside, the weak wood of the willow tree is an easy target for decay. Fungal growths form and the heart wood of the tree begins to rot. Keeping trees vigorous is a significant factor in avoiding a severe heart rot problem, because in healthy trees the rot will not spread to the entire tree. For control, prune trees into the desired shape when young and prune carefully for minimal wood exposure, to decrease area of potential infection sites. No chemical control is recommended, but because willow trees have weak wood, seek the assistance of a professional arborist to determine the sturdiness of your tree. If decay is advanced, a weakened tree structure may easily fall and poses a threat of injury to nearby structures, people and animals, according to North Dakota State University Agriculture.