Willow trees (Salix spp.) add interest to your yard with their cascading leaves. Unfortunately, when a willow gets blight disease, its awe-inspiring presence quickly changes to unsightly. Understand the blight disease that affects willow trees and put control measures in place the moment you suspect a problem.
1. Preventive Care
Provide your willow trees with the care they need for strong plants that have a better chance of avoiding and recovering from problems, such as blight. Grow willows where they will get full sun to light shade. While these deciduous trees will continue to thrive in nearly any type of soil, they perform particularly well in moist conditions. Willows also tolerate flooding, a wide range of pH levels and drought. Willows need substantial space for root growth and are often considered invasive as a result of their aggressively spreading roots. For best performance, grow willows in U.S. Department of Agriculture plant hardiness zones 2 through 9a.
2. Bacterial Blight
Willow trees are susceptible to a disease called bacterial blight. Caused by the bacterial pathogen Pseudomonas syringae, this disease affects the shoots and leaves of trees. Overwintering on bark, the disease invades the willow tree through openings, such as the tree's natural stomata or wounds. The disease travels throughout the tree through the system that carries water, becoming active in areas of new growth. Encouraged by cool, wet weather and deterred by warm weather, this disease is most prevalent in spring.
Examine your willows for early signs of bacterial blight, such as yellowing spots, or blights, on leaves. Brown spots may also appear. As they grow and expand, the spots darken to black and appear saturated with water. The black tissue also occurs along the center rib of the leaves. Damage includes the development of oozing lesions, dead twigs and malformed twigs that take on a hooked appearance, known as shepherd's crook.
Prune back blighted branches to decrease the severity of the disease on willow trees and to remove unsightly plant parts. Remove these plant parts during dry conditions to decrease the chance of disease spread or reinfection. Always sterilize equipment, such as pruning shears, between cuts and from one plant to the next. If the blight has extended to the trunk of the tree, remove the entire tree. If the blight has not spread throughout the entire tree and is concentrated on the leaves, the tree will likely heal on its own.
- University of Florida IFAS Extension: Salix Spp.: Weeping Willow
- University of California Statewide Integrated Pest Management Program: Willow -- Salix Spp.
- University of California Statewide Integrated Pest Management Program: Bacterial Blight -- Pseudomonas Syringae
- Kansas State University Research and Extension: Pseudomonas Blight of Trees and Shrubs
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