WSU Extension

Hortsense

Caption: Willow rust damage on upper leaf surface
Photo by: R.S. Byther
  
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Willow : Rust
(revision date: 4/28/2014)


Biology
Willow rusts are fungal diseases that begin in early summer, but are most noticed in late summer to early fall. Leaves first display yellow spots, which turn dark brown or black by late summer or early fall. Severe infections cause leaves to drop, sometimes resulting in considerable defoliation. The fungus overwinters on dead leaves and infected twigs or on alternate hosts. Alternate hosts for willow rusts include fir, larch, and Ribes species such as currants and gooseberries, depending on the rust species. Rust infections on willows are not typically a serious problem, although growth of young trees may be somewhat slowed by defoliation.
Management Options

Non-Chemical Management
  • Rake and destroy all fallen leaves beneath willow trees.
  • Avoid overhead watering and splashing water, which contribute to the spread of the disease.
Select non-chemical management options as your first choice!

Chemical Management


Apply when conditions favor disease. 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.
  • Spectracide IMMUNOX Multi-Purpose Fungicide Spray Conc
    Active ingredient: myclobutanil  |  EPA reg no: 9688-123-8845
  • This list may not include all products registered for this use.
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Caption: Willow rust damage on upper leaf surface
Photo by: R.S. Byther
Caption: Willow rust fruiting bodies on lower leaf surface
Photo by: R.S. Byther