WSU Extension

Hortsense

Caption: Douglas-fir Melampsora rust
Photo by: G.A. Chastagner
  
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Douglas Fir : Rust
(revision date: 4/23/2014)


Biology
Rust is a fungal disease infecting the needles of Douglas fir. Wind-blown spores infect the new needles in the spring. Yellow to orange bumps, or pustules, are found on the underside of needles in the spring or early summer. The infected needles are usually a discolored yellowish-green. If the disease pressure is very high, sunken red-brown cankers may be found girdling the current season's branches. Rust overwinters on the fallen leaves of black cottonwood and other poplars which are alternate hosts to the disease.
Management Options

Non-Chemical Management
  • Remove alternate hosts (black cottonwood and other poplars) near plantings.
Select non-chemical management options as your first choice!

Chemical Management


Make one application when shoots are 1 to 1.5 inches long. 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.
  • Bonide Infuse Systemic Disease Control
    Active ingredient: propiconazole  |  EPA reg no: 100-773-4
  • ferti-lome Liquid Systemic Fungicide II R-T-Spray
    Active ingredient: propiconazole  |  EPA reg no: 53883-184-7401
  • 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: Douglas-fir Melampsora rust
Photo by: G.A. Chastagner
Caption: Douglas-fir Melampsora rust damage
Photo by: G.A. Chastagner
Caption: Douglas-fir Melamspora rust
Photo by: R.S. Byther