The Salix, or willow genus, is a family of deciduous shrubs and trees. Willow trees are susceptible to a number of different diseases. Some diseases result in unsightliness, while others can cause tree death.
Willow trees are prone to fungal infections such as black canker and willow scab. They are also susceptible to a fungal infection called powdery mildew disease, as well as a bacterial infection called crown gall.
Black canker creates irregular brown or black wounds on stems between April and June. The wounds, called cankers, develop saucer-shaped fungal bodies filled with spores. Willow scab attacks new twigs and leaves, causing defoliation. The willow scab fungus and the black canker pathogen work together to create a serious disease called willow tree blight. Willow trees with powdery mildew develop white fungal spots on the leaves that grow together until they cover the entire leaf. Infected leaves curl, yellow and fall, resulting in defoliation. Willows with crown gall develop abnormal growths near the soil line. Severe infections cause decreased plant growth, dieback or plant death.
Willow blight is controlled by pruning out diseased plant parts and raking up leaf litter. Timed applications of appropriate chemicals help prevent disease symptoms. Powdery mildew infections are prevented by planting disease-resistant cultivars, by pruning out diseased plant parts and by using an appropriate fungicidal spray at the first sign of disease. Trees that are severely infected with crown gall should be removed and destroyed.
- Ohio State University Extension: Salix - Willow
- Cornell University Department of Plant Pathology: Black Canker
- Cornell University Department of Plant Pathology: Willow Scab
- University of Rhode Island Landscape Horticulture Program: Powdery Mildew on Shrubs
- University of Illinois Extension: Crown Gall
- University of Minnesota Extension: Disease Management Recommendations for Trees and Shrubs