Gary W. Moorman, Professor of Plant Pathology
|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||Destroy heavily infected trees. To protect trees not yet affected, apply a fungicide 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 a fungicide 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.|
| Stigmina needle blight ||Year-old needles turn yellow, brown and then fall in the Spring a year after infection. Brown needles 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 while the new, current year’s needles appear healthy. The dark fruiting structures sometimes appear to have fuzzy tops.||Stigmina lautii||Space trees and provide good weed control to ensure free air circulation around the tree. Apply a fungicide when new shoots are 1½ inches long and again 3 weeks later to protect young needles from infections that occur in May through June. For best control, apply the fungicide 3 consecutive years.|
Cytospora canker on blue spruce.
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