Apple Tree Diseases

The diseases that strike apple trees are all fungal and can be controlled and prevented in most cases. Proper care and a watchful eye can help keep the apple tree healthy and the crop abundant. When it comes to using a fungicide, check with your local garden center for what is best and legal in your area.

Scab

Scab is caused by a fungus known as the Venturia inaequalis. It will appear in late fall and early spring as round, black pimples on leaves that were infected the year before. The pimples release spores in the spring that are carried by wind and rain to other trees. The process can continue throughout the growing season. Leaves will fall from the tree, and infected fruit will mature unevenly and crack. The disease will not harm the tree itself, but it will do a great deal of damage to the leaves and fruit. Prune off any infected areas and destroy them. Do the same with the leaves that fall off in autumn. Keep the tree well pruned to improve air circulation. Cortland and McIntosh apples are very susceptible, but varieties likeLiberty, Freedom and Honeycrisp are resistant.

Powdery Mildew

Powdery Mildew, another fungus that attacks apple trees and other plants, looks like talcum powder and grows in warm, dry climates. However, it will not germinate without high humidity. Twig growth will be stunted, and the terminal bud will die off. Young apples will develop russeting or etching. Air circulation through the branches helps prevent the fungus, so do proper pruning. A sulphur spray will help control the fungus if it does break out. Akane, Red Delicious, Discovery, Golden Delicious, Liberty, Lodi, Macfree, Prima, Priscilla, Red Delicious, Redfree, Sir Prize, Spartan and Tydeman's Red are the varieties that are most resistant.

Fire Blight

Fire Blight is one of the most serious of the fungi that attack apple trees. Very few species are resistant. It attacks the shoots and turns them brown or black. The flower blossoms will wither away and die. Reddish lesions appear on the bark and will ooze out an orange-brown liquid during warm weather. Check the apple tree in the winter, and if you notice any branches that have visible cankers, prune them off. As with the other fungus infections, proper pruning will go a long way toward prevention. Akane, Baldwin, Liberty, MacFree, McIntosh, Northern Spy, Nova Easygro, Novamac, Prima, Redfree, Red Delicious, Winesap and Stayman are the most resistant varieties.

Black Rot

Black Rot is a fungus that appears when the fruit is ready to harvest, usually at a place where the apple itself has been wounded. It looks like small brown spots on the apples. The spots will expand, turn darker and then black. The disease will also attack the bark, twigs and fruit and will winter over on them. Prune out any infected wood and fruit, destroy them and use an fungicide.

Cedar Apple Rust

Cedar apple rust will cause pale yellow spots as small as the head of a pin on the top surface of the apple tree leaves. The spots will get larger and turn a bright orange on both the leaves and the fruit. The rust actually originates on other types of trees including the Cedar, Juniper and Hawthorn, and then spreads to the apple trees. Spray the apple trees in the spring with a fungicide, and keep apple trees a minimum of 300 feet from any red cedar trees. Resistant varieties include the Liberty, Nova Easygro, Novamac, Priscilla and Redfree.