Tree Diseases, Fungus and Black Rot

Types

• Fungal diseases such as black rot and frogeye leafspot are caused by Botryosphaeria obtusa. These two fungal diseases are common in many trees, including apple trees. Foliage diseases such as Marssonina leafspot are caused by the fungus Marssonina and affect cottonwood and aspen trees. Heart rot is caused by fungi that decays wood and only attacks trees under stress, not healthy trees.

Symptoms

• Black rot and frogeye leafspot cause fruit to develop light brown spots, which turn darker in color and form bands around the fruit. Fruit eventually turns brown and decays, but remains on the tree. Marssonina leafspot causes dark brown specks with yellow rings to develop on foliage. Spots can turn into large, dead patches. Trees infected with heart rot fungi, often have mushrooms on their trunks. Fruiting bodies signal severe decay of heart wood.

Control

• Good cultural practices and proper sanitation are important to prevent fungal diseases in trees. Avoid wounding trees during mowing or pruning, as injuries provide fungi with an easy entry to trees. Fungicides are often effective in preventing and eliminating fungal diseases. Contact your local extension office for advice on chemical control.