Worms are more than happy to eat your apples or damage your apple tree, but the pests are not your common earthworms. Knowing what type of worm is invading your apple tree is the first step toward stopping the infestation, and you can identity the worm by its physical appearance and attack patterns.
An apple maggot causes extensive damage to the fruit on your apple tree when in its larval stage, which lasts around a month. An adult female maggot lays eggs below the skin of the apples that hatch in about a week. The maggot larvae are 3/8-inch long, white worms, and as they grow, they eat your apples from the inside out.
Organic methods, including the placement of sticky molasses traps around the tree, can be used to curb your problem and prevent a reinfestation of apple maggots. Chemical pesticides, such as Diazinon, are used to control an outbreak.
The larvae of a codling moth burrow into the apples and destroy nearly all of your fruit if left unchecked. The female adult codling moth deposits the eggs on the apple tree's fruit or leaves, and when the eggs hatch, the worms tunnel into nearby fruit on the tree. The codling moth larvae are small white or pink worms, usually about 1/2 inch long. Look for the red-brown waste they leave behind inside the fruit and on the peel; it's known as "frass."
Clean around your tree and remove fruit showing signs of infection immediately. Codling moth traps can be hung in the tree to diminish the population. Chemical alternatives, such as Spinosad, are available for eliminating codling moths.
Apple Green Fruitworms
Apple green fruitworms look like green caterpillars and vary in length. The larvae, usually a lighter shade of green than the adult worms, eat both your apples and the leaves of your apple tree. Full-grown apples are not shaped correctly and have cavities. Green fruitworms may not become a widespread problem, as the worms don't spread quickly, but you can control the pest with common insecticides or organic control methods, such as the Entrust version of Spinosad.
Two different types of common tent caterpillars damage apple trees: forest and western. Both kinds grow to about 2 inches long, but a forest caterpillar is blue with white and black patterns, while an adult western caterpillar is black and orange. Tent caterpillars spin silky "tents" on the branches of apple trees and eat the leaves branch by branch. A healthy tree can usually recover from tent caterpillar damage, but a diseased tree or a tree in a rough climate may die if the caterpillars are not controlled or the infestation is widespread.
Removing and destroying the egg deposits -- brown or gray masses that resemble Styrofoam -- on your apple tree helps control a tent caterpillar problem. Some environmentally friendly pesticides, such as Dipel, are effective against tent caterpillars.
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