Apple Tree Diseases

Apple orchards are susceptible to many diseases.

For some gardeners, apple tree diseases seem to run rampant through their orchards each year. While this particular fruit tree is easy to grow, it certainly has its share of problems. Luckily, many apple tree diseases are easy to deal with so even a neophyte gardener can diagnose and treat them.

Learn to Spot a Sick Apple Tree

There are over two-dozen diseases that are associated with specific types of apple trees. However, some of these diseases are common among all apple tree varieties. These diseases are as follows:

Apple Scab

Apple scab begins in early spring. It can be found on the underside of the leaves where it begins, then spreads to other parts of the tree. The lesions can be found on leaves, blossoms, sepals, petioles, pedicels, shoots and bud scales. As the scab spreads, it is most evident on the young leaves as they begin to curl, twist, dwarf and become deformed.

The scabs can be identified at first as small, light brown areas on the undersides of the leaves. As the scab progresses, the brown areas turn dark brown and black as the cells die. Some leaves may be entirely covered with the brown spots, and leaves in this condition are often referred to as "sheet scab."

The fungus that causes apple scab (V. inaequalis) over winters in the infected trees, even in cold climates. Both home orchardists and commercial growers use a combination of treatment programs to control the disease. This includes choosing disease resistant cultivars, sanitation (removal of leaves and dead fruit from around the tree at the end of the growing season) and chemical treatments.

Apple Mosaic Virus

The apple mosaic virus is common in most apple tree varieties. Yellow or cream-colored spots that appear on the leaves in early spring can identify the virus. The spots become larger as the virus spreads on the leaves. Once warm summer weather sets in, the leaves will turn brown and die. This virus is most prevalent in the Golden Delicious and Jonathan varieties, causing the most damage on these trees. While it is still possible to have a crop of apples after the virus has infected a tree, it may be diminished by half in affected trees. There is no known treatment once a tree has been infected with the virus.

Black Pox

Black pox (Helminthosporium papulosum) is caused by a fungus that over winters in the infected trees. It is most common in warmer regions and predominantly affects the Rome Beauty and Grimes Golden varieties. Black, shiny, cone-shaped lesions that form on new twig growth identify this fungus. Lesions also appear on the fruit, which are small and black and eventually will appear as sunken in. Leaves also will show signs of the disease, first as red circles on the leaves that will eventually turn into a brown or purple color.

The treatment for this disease is sanitation and chemical application. Cleaning up leaves and fruit from the ground by the end of the growing season and applying a fungicide spray will help to eliminate the disease and stop it from spreading to other nearby trees.

Powdery Mildew

Powdery mildew (Podosphaera leucotricha) is a disease that affects many apple trees in mild climates. It doesn't need wet or rainy conditions to proliferate. The fungus over winters in dormant blossoms. Longitudinally folded leaves identify this disease in the spring, as well as a gray-white powder coating on the twigs, resulting in stunted twig growth. If left untreated, it will result in blossoms dropping prematurely from the trees and overall stunted growth of the tree. The disease can be treated by implementing a mildewcide program and by pruning away whitened terminal shoots on the trees.

White Rot

White rot (Botryosphaeria dothidea), or bot rot, is common in southern climates. The white rot only infects the fruit and wood, not the leaves. Infections occurring on limbs and twigs are identified by small circle-shaped spots and blisters. These spots will continue to enlarge during the growing season, eventually causing the bark of the tree to become orange in the affected areas and peel from the tree. In severe cases, the disease can cause girdling of the limbs and tree.Fruit rot will also occur and is identified by the appearance of small, sunken in brown spots in light-skinned varieties. In red-skinned varieties, the spots appear as white or light brown in color.

The disease can be treated with chemicals and with pruning of affected and dead wood each year. Fungicide should be applied throughout the growing season, from bloom throughout the harvest.

Stave Off Apple Tree Diseases

Apple tree diseases can be avoided in many cases by selecting and planting healthy, disease free rootstock. Carefully monitoring trees in the spring can help gardeners identify many of the diseases so treatment can begin early. Finally, sanitation is of great importance in any orchard. Prompt removal of dead leaves and rotting fruit as well as a regular pruning program can help stave off many infectious diseases.

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Apple Tree Diseases