Douglas Fir: Rhabdocline needle cast

categories: Conifers Douglas Fir Douglas Fir Diseases Ornamentals

revision date: 2024-06-05 02:07

reddish brown blotches on Douglas fir needles against a black background.
Douglas-fir Rhabdocline needle cast
Photo by: R.S. Byther


The first symptoms of this fungal infection are many tiny yellow spots on the current season’s needles appearing in late summer or fall. By spring, these spots have expanded and become characteristic dark reddish-brown blotches. The blotches on the underside of the needles later swell and split open to reveal orange-brown fungal structures. Diseased needles typically are cast (dropped) by late June. Severely diseased trees may retain only the current season’s needles and be weakened. The disease is favored by high humidity. Rhabdocline needle cast may be confused with Swiss needle cast.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

  • On small trees, prune and destroy diseased branches.
  • Avoid overhead watering while new foliage is growing.
  • In Christmas tree plantations, remove and destroy any infected trees.
  • Good air circulation is important for disease prevention. Do not plant in areas with poor air drainage and space trees to provide good air circulation.
  • Remove weeds around trees, thin canopy, and prune lower branches to help reduce humidity around trees.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

  • Make first applications when new growth is 1 to 2 inches long and an additional application 3 weeks later.
  • 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

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.

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