WSU Extension

Hortsense

Douglas Fir
 
Disease
Armillaria root rot 
Laminated root rot 
Rhabdocline needle cast 
Rust 
Stem cankers 
Swiss needle cast 
Upper stem canker 
Yellow-green mottle syndrome 
Insect
Aphids 
Coneworms 
Cooley spruce gall adelgid 
Douglas fir needle midge 
Douglas fir tussock moth 
Douglas fir twig weevil 
Sequoia pitch moth 
Silverspotted tiger moth 
Spruce spider mite 



print version| pdf version| email url    
Caption: Douglas-fir Swiss needle cast
Photo by: R.S. Byther
  
Douglas Fir : Swiss needle cast
(revision date: 4/23/2014)


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


Non-Chemical Management
  • 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.
Select non-chemical management options as your first choice!

Chemical Management

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.
  • Bonide Fung-onil Multi-Purpose Fungicide Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 60063-9-4
  • GardenTech Daconil Fungicide Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 67572-82-71004
  • Ortho Max Garden Disease Control Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 239-2522
  • This list may not include all products registered for this use.
Images

+ Show larger images

 
Caption: Douglas-fir Swiss needle cast
Photo by: R.S. Byther
Caption: Douglas-fir Swiss needle cast
Photo by: R.S. Byther
Caption: Douglas-fir Swiss needle cast: close-up
Photo by: R.S. Byther