Description: Anthracnose is a disease that has decimated much of the native Dogwood populations in the forests of the United States. Dogwood anthracnose affects all above ground parts of the host tree: leaves, flowers, current-year shoots, trunk sprouts, bark and cambium, fruits and seeds.
Symptoms: In mid-May through June, shortly after the leaves have expanded, spots and blotches of varying shapes and sizes appear on infected trees. These spots have a tan center and a purple or reddish margin. On the underside of the leaf, tiny black or brown spots may appear beneath the blotches. The flower ‘petals’ or bracts also show reddish or brownish blotches. In some cases, entire leaves are infected and die. The dried leaves remain on the stem throughout the fall and winter.
Once the whole leaf has been affected, the infection can spread through the petiole into the stem, causing cankers. Cankers are usually tan depressions and produce the same tiny black or brown spots as are on the undersides of the leaves. Over time, the infection of twigs and shoots kills the branch, starting with those lowest on the tree and moving up. The tree may attempt to send out shoots to compensate for the loss of leaves but the fungus easily infects them as well. Once sprouts are infected the fungus moves quickly into the trunk. Severe cankers will split and buckle the bark. Affected trees in shady locations generally die within 1-3 years. Others in sun-exposed locations often survive and show varying degrees of severity from year to year.
In the spring large amounts of spores are produced inside the tree by the reproductive structures – the black or brown spots. These spores ooze out in slimy beige clusters. Spores are carried by splashing rain, insects and birds.
Action: Healthy trees are much more able to cope with disease than stressed trees. Keep trees stress free by applying 3-4 inches of mulch around the base, but not touching the trunk. Water during dry periods. Fertilize moderately. Avoid overhead irrigation. Avoid mechanical damage, such as mowers. Rake and remove leaves each fall. Prune diseased branches. Pull dead leaves from the tree. Prune any water sprouts that grow from the trunk. Improve air circulation around trees to help dry foliage and reduce infection. If possible, prune in dry, hot weather. Disinfect the pruner blades in a solution of 70% rubbing alcohol between cuts. Fungicides are also available and can be applied in the spring, starting at bud break and continuing every 10-14 days until the leaves are fully expanded. Further sprays may be necessary if it is unusually wet.
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