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

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.

Rhabdocline needlecast symptoms and signs.

Rhabdocline fruiting structures.

Swiss needlecast fruiting structures

Diplodia twig blight. Note black fungal structures on the curved part of this tip.