WSU Extension


Bacterial twig blight 
Marssonina leaf & twig spot 
Twig blight (Venturia) 
Poplar-and-willow borer 
Satin moth 
Spiny elm caterpillar 

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Caption: Willow bacterial twig blight
Photo by: R.S. Byther
Willow : Bacterial twig blight
(revision date: 3/22/2021)

Bacterial twig blight of willow is caused by the same bacterium that causes bacterial blight of lilac and other woody ornamentals. The disease attacks twigs and branches, causing them to die back. Leaves on affected branches turn brown, wilt, and drop, sometimes resulting in severe defoliation. Young shoots are often girdled. Affected branches may show brown streaks in the wood when cut. The bacterium overwinters in the twig and branch cankers and reinfects new leaves in the spring.
Management Options

Non-Chemical Management
  • Prune and destroy affected twigs and branches (when practical).
  • Maintain proper plant nutrition. Healthy plants resist disease better.
  • Avoid overhead irrigation.
  • Space plants properly and prune to provide good air circulation.
Select non-chemical management options as your first choice!

Chemical Management

Monterey Liqui-Cop Copper Fungicidal Garden Spray can only be used on weeping willow. For best results, apply in fall after leaves drop. However, some labels may not allow this timing. Always follow label instructions. Homeowners should not make foliar applications to trees over 10 ft tall. Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Monterey Liqui-Cop Copper Fungicidal Garden Spray
    Active ingredient: copper-ammonia complex  |  EPA reg no: 54705-7
  • This list may not include all products registered for this use.

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Caption: Willow bacterial twig blight
Photo by: R.S. Byther