Skip to main content

Alternaria Leaf Blotch

Alternaria leaf blotch is caused by the fungus Alternaria mali. It affects apples, and it is mainly encountered in southern states. The fungus overwinters in dead leaves, infected twigs, and dormant buds. It becomes active about a month after petal fall, and it is most prolific in wet weather when temperatures range between 75°F and 85°F. Infection will occur if surfaces are wet for 5.5 hours or longer.

Infected leaves will develop "frogeye" spots, starting as small purplish round spots and developing into larger, irregular brown spots with dark borders. When infection occurs on petioles (leaf stems), the leaf will yellow and drop. This disease can be confused with black rot, but unlike black rot it will not affect fruit and it will not cause cankers. The primary concern with alternaria is severe defoliation and consequent weakening of the tree if infection levels are high.

Alternaria infections are associated with mites, and these must be controlled if alternaria is present. Removing debris and mowing or burning fallen leaves is always good practice when it comes to fungal diseases. If you live in an area where alternaria is a problem, consider planting resistant varieties such as Granny Smith, Jonathan, Jonagold, Mutsu (Crispin), McIntosh, and Gala. In some cases, an application of fungicide may be necessary.

For more information, see the North Carolina Extension Factsheet on Leaf Spots of Bother: The Troublesome Three.

Featured Products

A few things we're loving right now...

Historic American Fruit Trees

These apples and pears were grown in North America during the Colonial Era and through the time of the American...

Winecrisp™ Apple on G.11

A beautiful purple, late-season, disease-resistant dessert apple.

Flemish Beauty Pear on OHxF 87

A hardy pear with exceptionally good flavor.

Backyard Fruit Trees

Looking for easy-to-grow trees for your home orchard? Choose from these apple, peach, pear, plum, and cherry varieties that...