Apple Tree Diseases

If you own an apple tree, worrying about apple tree diseases can seem like a full time job. Although apple trees are susceptible to a number of infections, treatment is often straightforward and prevention can be as simple as cleaning up the area around your apple tree.

Recognizing Apple Tree Diseases

Apple trees are vulnerable to a number of unique diseases and several that are common to most flowering trees. Keeping a careful eye on your apple tree and responding quickly to signs of trouble are the best ways to keep your apple tree healthy. Here's what to look out for:

  • Apple Mosaic Virus - This common (and devastating) infection appears as cream or yellow spots on newly developing leaves. The spots will increase in size as leaves mature. In the summer, leaves will turn brown and fall from the tree. Golden Delicious and Jonathan varieties are most vulnerable to this virus. There are no known countermeasures for this virus.
  • Apple Scab - Effecting foliage and fruit, apple scab first appears as dull gray areas on leaves that soon turn olive green and velvety. Fruit will develop olive green circular lesions about ¾" in diameter. Apple scab is control with regular applications of fungicides throughout the growing season. The critical period for fungicide application is early in the season during bud formation and flowering.
  • Cedar Apple Rust - Produced by galls on infected Red Cedar trees, rust spores are carried by the wind to infect nearby apple trees. Cedar rust first appears as small yellow spots on the upper surface of leaves. Unchecked, cedar rust can quickly lead to defoliation of the infected tree. If possible, remove any cedar trees within a ½ mile radius. Cedar rust specific fungicides are effective in combating infection.
  • Fire Blight - This bacterial disease can be quite destructive but is also erratic in its outbreak patterns. Fire blight may appear on the bark of the tree as dark, discolored sections of bark on the tree. These depressions may be cracked around the edges and be covered in black sooty spores. Fire blight may also infect blossoms, turning them dark brown and wilted. Pruning and destroying infected plant material and copper sulfate-based fungicides should both be used to combat infections.
  • Powdery Mildew - Often seen in warm, humid conditions, powdery mildew will show as white patches on young leaves and twigs. Fungicides are an effective countermeasure, but properly pruning your apple tree to allow for light penetration and air circulation is the best preventative.
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