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Evergeen Tree Diseases

By Regina Sass ; Updated September 21, 2017
Even the largest evergreen can be brought down by disease.
evergreen image by FFprod66 from Fotolia.com

Wet spring weather and standing water make breeding grounds for fungal diseases that can be fatal to evergreen trees. Proper maintenance goes a long way in preventing the diseases from getting started. Leave space between the trees so air can circulate, keep the area clean and the soil well drained, and you will give your trees more than a fighting chance.

Cytospora Canker of Spruce

Cytospora canker is the main cause of death in Colorado blue spruce, and it only strikes trees that are grown out of their native range. Colorado blue spruce is not the only variety that is vulnerable. Norway spruces and, to a lesser degree, Koster's blue spruce and Douglas fir also can be victims. The first symptom is the browning of the needles and dying off of the lower branches. The disease progresses up the tree until there are more dry, brittle, infected branches than there are healthy ones. In rare instances the disease attacks the top of the tree, and the lower ones remain healthy. The cankers form on the trunk and are hard to see because the trunk bark does not become discolored. You may notice amber, purplish-white or all-white patches of resin on the bark in areas where cankers have formed. Remove a thin layer of the outer bark and, if you see tiny, black, pinhead-like fruiting bodies of the fungus, the diagnosis is confirmed. The are no fungicides for cytospora canker. The only thing that can be done is to remove all of the infected branches. Give the tree a good dose of fertilizer and make sure the soil is well-drained.

Sphaeropsis Blight

Sphaeropsis blight is a fungal disease that attacks mostly pine trees. The fungus goes after the new, healthy needles, usually on trees that are at least 30 years old. If the tree is under stress from being transplanted or another disease, the twigs also can be attacked. New branches and needles will be stunted, twisted and brown, usually on the bottom of one side of the tree. Resin may appear on the young stems and older branches that have suffered injury. All infected twigs and cones have to be removed and the tree given a good dose of fertilizer. There are fungicides to combat this disease.

Phomopsis Blight

Phomopsis blight attacks trees in the cypress family, especially eastern red cedar, junipers, American and Oriental arborvitae, Douglas-fir, European larch and jack pine. The first sign is the die-back of the new shoots, which will change from the normal light yellow-green to red-brown and finally to ash-gray. This disease only kills new growth. If older parts are affected, it is another disease. Phomopsis blight will last through the winter on stems that were affected the previous year and strike again in spring. Repeated infections can result in the death of the tree. Prune out and dispose of all infected parts and sterilize the pruning shears after each cut to prevent the spread of the disease.