Spruce Diseases
Gary W. Moorman, Professor of Plant Pathology
| Disease | Symptoms | Pathogen/Cause | Management |
|---|---|---|---|
| Cytospora canker | Sunken dead areas of bark and underlying wood form on the lower branches of the trees girdling small branches in 1 or 2 years and large branches after several years. Resin flows out of the cankers and may drip down on lower branches. Scattered lower branches die. Branch death progresses up the tree. | Leucostoma kunzei (Cytospora) | Since the fungus readily infects wounded tissue but remains latent in the tree without causing symptoms until the tree is drought stressed, fungicide sprays cannot be effectively timed to prevent this disease. Select the planting site carefully, avoiding drought prone sites. Anticipate the future needs of the mature tree and consider whether the site has the potential to supply the water required of a specimen 50 to 60 feet tall. Prune infected branches. Blue, white, red, black, Engelmann, and Norway spruces are all susceptible to this disease. |
| Needle rust | Year-old needles are cast after turning rust colored in the spring. Blue spruce is very susceptible, as are black, Engelmann, red, Sitka, and white spruces. | Chrysomyxa weirii | Notify the Bureau of Plant Industry immediately to obtain a positive diagnosis. Destroy infected trees. To protect trees not yet affected, apply chlorothalonil first when 10 percent of the tree is in bud break, again 1 week later, and again 3 weeks after the first spray. |
| Rhizosphaera needlecast | Year-old needles turn lavender in color and have tiny, black fungal fruiting structures in rows on either side of the midvein on the underside of the needle. Large bare areas develop on the tree as needles fall. | Rhizosphaera | Space trees and provide good weed control to ensure free air circulation around the tree. Apply chlorothalonil when new shoots are 1½ inches long and again 3 weeks later to protect young needles from infections that occur in May through June. Some locations have an additional infection period in September and October. Blue and Engelmann spruce are highly susceptible. White spruce is somewhat susceptible. Norway spruce is relatively resistant. |
Cytospora canker on blue spruce.
Rhizosphaeria needlecast.
Needlecast infection and symptom timing.
Active Ingredient and Trade Name of the Chemical
| FRAC Group No. | Risk Level | Class | Active ingredient | REI Restricted Entry Interval | Trade Names (EPA Reg. no) |
|---|---|---|---|---|---|
| M | 1 | Chloronitrile | chlorothalonil | 48 | Daconil (50534-9) |
| 12 | Echo (60063-7), PathGuard (60063-7-499), Concorde (72167-24-1812), Pegasus (72167-24-1812) |
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