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Apple Valley
7100 147th St. W.
Apple Valley, MN 55124
Ph: (952) 953-2500
Common Tree Diseases
This is most commonly seen on white oak and ash trees, especially after cool and wet spring weather conditions. It is a leaf spot caused by a fungus that results in irregular patches of dead leaf tissue, leaf wilting, and premature leaf fall. Anthracnose is essentially a cosmetic problem and does not cause a significant impact to the tree. These two pictures show typical anthracnose symptoms on white oak.
Leaf with Anthracnose  Leaf with Anthracnose

Apple Scab 
This is most commonly found on apple and crab apple trees. It is a leaf spot caused by a fungus. Leaves are covered with dark-green to black spots and fall prematurely. Apple scab occurs in spring and continues if moist conditions persist. Many disease resistant crab apple varieties are now available for planting.

Cytospora Canker
This is most commonly seen on Colorado spruce. It is a fungal disease that kills the cambium layer (inner bark), which causes branch and stem cankers. As cankers enlarge and encircle a branch, needles turn brown and the branch dies. Once a canker has become established in the main stem, food and water are cut off, and death occurs above that point.

Fire Blight 
This is common to mountain ash, apple, hawthorn, crab apple, and other fruit-bearing plants. Leaves, twigs, and blossoms wilt and turn black as if they have been scorched by fire.

These are abnormal growths caused by insects and fungi. Galls vary widely in shape and size and can be found on leaves, flowers, branches, and trunks. Most species of evergreens, deciduous trees, and shrubs are susceptible.

Iron Chlorosis 
This is most commonly seen on oak, maple, and river birch. It is usually caused by lack of iron, which results in pale-green to yellow leaf color with leaf veins remaining green. Generally iron chlorosis indicates a root problem rather than lack of iron in the soil.

Rhizosphaera Needle Cast
This is most commonly found on lower branches of Colorado spruce, especially where trees are growing in groups or rows where airflow is restricted. This needle-cast disease is caused by a fungus that thrives in dark and moist conditions. Needles on lower branches turn brown and fall prematurely, resulting in branch death.