CAHNRS > Hortsense > Fact Sheets > Ornamentals > Conifers > Douglas Fir > Douglas Fir Diseases > Douglas Fir: Swiss needle cast

Douglas Fir: Swiss needle cast

categories: Conifers Douglas Fir Douglas Fir Diseases Ornamentals

revision date: 2023-01-31 12:00

Douglas fir bough with some dead leaves.
Douglas-fir Swiss needle cast
Photo by: R.S. Byther

Biology

This fungal disease causes infected needles to become off-color and mottled yellow or brown. The needles may turn completely brown and are usually dropped prematurely, often in early spring. Infected needles may also remain green and attached to the branches. Older needles typically drop first. Severely diseased trees may have only the current season’s needles remaining on the branches. On the underside of infected needles, along either side of the midrib, straight rows of tiny black dots appear. These dots (fungal structures) are most common on needles one year old and older. Swiss needle cast is favored by high humidity. This disease may be confused with Rhabdocline 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!

  • Good air circulation is important in disease prevention. Do not plant in areas with poor air drainage and space plantings to provide good air circulation.
  • Remove weeds around trees, thin canopy, and prune lower branches to reduce humidity around tree.

Chemical Management

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

  • Apply once when new spring growth is 1 to 2 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

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

  • Bonide Fung-onil Multi-Purpose Fungicide Concentrate
    Active ingredient: chlorothalonil [EPA registration number: 60063-9-4]
  • GardenTech Daconil Fungicide Concentrate
    Active ingredient: chlorothalonil [EPA registration number: 67572-82-71004]
  • Ortho Max Garden Disease Control Concentrate
    Active ingredient: chlorothalonil [EPA registration number: 239-2522]
  • This list may not include all products registered for this use.

Additional Images