Douglas Fir: Swiss needle cast
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.
Use Integrated Pest Management (IPM) for successful plant problem 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.
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.
Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.