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Douglas-Fir Diseases

Informational table showing disease name, symptoms, pathogen/cause, and management of Douglas-Fir diseases.

Updated:

July 31, 2016

Disease	Symptoms	Pathogen/Cause	Management
Rhabdocline needlecast	During March through May, yellow spots form on the previous year's needles. These enlarge and become reddish-brown patches on an otherwise green needle. These needles then fall.	Rhabdocline pseudotsugae and R. weirii	Place plants in locations where good air circulation is available. Maintain good weed control so that air circulation is not impeded. When approximately 10 percent of the buds have broken in the spring, apply a fungicide. Repeat the application 1 week later and again 3 weeks after bud break. If spring is cold and new shoots mature slowly, apply a fourth spray 2 to 3 weeks after the third spray.
Swiss needlecast	From March through June, the previous year's needles gradually brown and fall. Rows of tiny, black fungal fruiting structures line the midrib on the underside of the needles. A magnifying glass is needed to see individual structures.	Phaeocryptopus	Place plants in locations where good air circulation is available. Maintain good weed control so that air circulation is not impeded. When new shoots are 1½ inches long, apply a fungicide. Repeat the application 3 weeks later.
Twig blight	Twig tips curl downward, turn dark brown, and die. Small black fungal fruiting structures dot the dead tissue.	Diplodia	Prune and destroy blighted tips.