At one time, apple trees were grown only in the northern part of the United States, but now there are fruit-producing varieties available for every growing area. However, the same insect pests attack all apple trees throughout the country. It is impossible to grow perfect apples without an insect-control program in place that involves a regular spraying schedule. Because every growing area is different, contact your local county agricultural extension office for information on currently approved insecticides and the correct time to spray in your area.
The plum circulio is a particularly destructive pest of apple trees. It overwinters in the ground as a beetle, then crawls up the tree when the weather warms and lays eggs in the developing fruit. When the egg is laid, the female cuts a distinctive crescent-shaped wound into the fruit. The eggs hatch in the fruit and the larvae feed inside the fruit, causing it to eventually fall from the tree. After the fruit is on the ground, the worms leave the damaged fruit, burrow into the ground, mature into beetles and begin the cycle again.
Aphids congregate on new leaf buds where they overwinter, waiting for the new leaves to emerge. They feed on the sap of the tree, damaging and weakening new growth. Aphids have a lot of natural enemies, so careful application of insecticide is important so you don't damage populations of beneficial insects.
Coddling moths produce several generations each year with each generation becoming more damaging to the fruit. The first generation comes from eggs laid on the leaves of the apple trees. The worms eat the leaves and then move down to the developing fruit. They feed on the fruit, then migrate into the bark of the tree where they pupate. Then, the next generation of adults, which are moths, appear and lay eggs directly on the fruit. When the eggs hatch, the worms burrow into the fruit, causing extensive damage. When they are ready to pupate, they once again find a location near the tree and begin the cycle again.
Spider mites are tiny insects that live on the underside of leaves. They overwinter in the soil and in the crevices of the bark of the apple tree. The spider mites feed on the sap of the tree as they pull it from the leaves. The first symptoms of spider mites are a scorched appearance of the leaves. In heavy infestations, you can see the tiny yellow-and-brown insects congregating on the undersides of infested leaves. During a severe infestation, webbing appears around the damaged leaf structures and the spider mites are clearly seen in the webbing material.