Douglas Fir Diseases
Gary W. Moorman, Professor of Plant Pathology
|
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 chlorothalonil. 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 chlorothalonil or azoxystrobin. 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.
Active Ingredients and Trade Names of the Chemicals
| FRAC Group no. | Risk Level | Class | Active ingredient | REI Restricted Entry Interval | Trade names (EPA Reg. no.) |
|---|---|---|---|---|---|
| 11 | 3 | Strobilurin | azoxystrobin | 4 | Heritage (10182-408) |
| M | 1 | Chloronitrile | chlorothalonil | 48 | Daconil (50534-9), PathGuard (60063-7-499) Concorde (72167-24-1812), Pegasus (72167-24-1812) |
Fungicides and Fungicide Resistance Management - Certain fungicides, usually systemic fungicides, are said to be 'at risk' to the development of resistance if they are used repeatedly. See the Risk Level in the above table (1 = low risk; 3 = high risk). The Fungicide Resistance Action Committee has developed a numbering system in which chemicals with the same FRAC Group number have the same mode of action (See http://www.frac.info/frac/index.htm ). It is recommended that chemicals at high risk be used sparingly and in rotation or mixed with chemicals with different modes of actions (different FRAC number).
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