Douglas Fir: Rust

• Categories: Conifers Douglas Fir Douglas Fir Diseases Ornamentals
• Last review date: 2026-04-27 11:09

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 host to the disease.

Management Options

See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.

Non-chemical Management

Select non-chemical management options as your first choice!

• Remove alternate hosts (black cottonwood and other poplars) near plantings.

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.

Approved Pesticides

If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.

• Bonide Infuse Systemic Disease Control
  Active ingredient: propiconazole
  EPA registration number: 100-773-4
• ferti-lome Liquid Systemic Fungicide II R-T-Spray
  Active ingredient: propiconazole
  EPA registration number: 53883-184-7401
• Spectracide IMMUNOX Multi-Purpose Fungicide Spray Concentrate
  Active ingredient: myclobutanil
  EPA registration number: 9688-123-8845
• This list may not include all products registered for this use.