- The two most common, and easiest to remedy, insects that cause problems for apple trees are codling moths and apple maggots. The problem begins with the adult insect. The apple maggot adult is a black and yellow fly that lays eggs in punctures and cuts on the apple fruit. The eggs produce white or yellowish worms that feast on the apple. A codling moth will lay its eggs on twigs and leaves close to the blossoms or young fruit, and, like the apple maggot, the worms find their way into the apple. Commercial sticky traps, usually colored cardboard with a sticky substance on them, placed four per tree, will capture the adults. Sprays may be needed if the egg infestation has already occurred.
Less common insects that harm apple trees are aphids, mites, scale weevils and gypsy moth caterpillars. Aphids and mites attack the leaves, leaving them yellow colored and distorted, while scale weevils and gypsy moth caterpillars cause foliage loss and eat bark. - Powdery mildew particularly plagues apple trees that grow in high humidity areas. The fungus appears as a white powdery film that covers twigs, leaves and blossoms. It will kill the blossoms, stunt twig growth and damage and scar young apples. Applying a fungicide, as directed weekly in the spring, to your tree will control and prevent powdery mildew.
Fire blight is also troublesome to apple trees, causing shoots, foliage and blossoms to die and lesions on the bark. If the fire blight infected areas are not eliminated from the tree by pruning, the tree will eventually die. - The fungus black rot will damage the fruit by developing small brown spots on the apple when the fruit is close to maturing. The spots expand and turn black, ruining the fruit. Black rot can also attack the bark and twigs of a tree, and infected areas should be pruned out, while the rest of the tree can be treated with a fungicide, per the directions.
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