WSU Extension

Hortsense

Caption: Birch rust
Photo by: R.S. Byther
  
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Birch : Rust
(revision date: 4/28/2014)


Biology
Birch rust is a fungal disease which first appears on leaves in early summer. Initially, small yellow angular spots develop on leaves. These may expand into brown spots with yellow edges. Later in the summer, reddish or yellow pustules (powdery-looking clusters) can be found on the underside (and sometimes on the upper surface) of leaves. By late summer, dark brown to black fungal structures may be found as well. Trees may drop infected leaves, sometimes resulting in severe defoliation. This disease can predispose young trees to winter damage or other diseases. Infection is typically worse in cool, wet conditions. The alternate host for birch rust is larch, but larches need not be present for disease development on birches.
Management Options

Non-Chemical Management
  • Do not plant in low, moist areas with poor air drainage and circulation.
  • Remove fallen leaves and debris from beneath birch trees to reduce reinfection.
  • Prune canopy to improve air circulation.
  • Limit overhead watering to times when foliage can dry quickly.
Select non-chemical management options as your first choice!

Chemical Management


Apply to protect leaves just before the disease is expected to appear if it has been a problem previously. 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: Birch rust
Photo by: R.S. Byther