How to Keep Worms Out of Fruit Trees
Apple worms, the ones you bite into while eating an apple, (or pear), are the larvae of the codling moth. They can ruin a large amount of your fruit when it comes time to harvest if you don't take steps to prevent them. Codling moths overwinter as larvae under flaps of bark on the apple tree, in nearby debris, under shingles, etc. In the spring, the larvae pupate and a moth emerges to begin laying eggs soon after apple blossoms have faded. Eggs are laid on tiny newly forming fruit or nearby leaves. The eggs hatch and the larvae enter the calyx or blossom end of the apple where it tunnels into the core or the apple to feed.
Management of apple worms begins in the fall with the elimination of debris around apple trees, and actual physical removal of loose flaps of bark from the tree -- without damaging the tree, of course. Cleaning your yard is not likely to be enough action to keep your apples free of worms as coddling moths have been documented flying up to a mile in search of an apple tree!
The codling moth has two generations in Colorado. It is important that the timing of controls coincide with the hatching of eggs before the worms have entered the apples. This generally is around mid-June (first hatch) and late-July (second hatch). Egg hatch can extend over several weeks, however, so it is often advisable to maintain spraying throughout the summer at two-week intervals following the first egg hatch.
To be most effective, spray treatment should start shortly after petal fall and continue throughout the summer thoroughly coating the fruit. Clusters of touching fruits should be thinned so that worms cannot enter the places where touching fruits prevent coating of apples.
Organic: Pheromone traps, sticky traps treated with a sex-attractant, can be hung in apple trees to help control high populations of adults and they are a good indicator of peak periods when moths are out and laying eggs. Egg hatch generally follows in 7-14 days.
Insecticides: Fertilome Fruit Tree Spray, Malathion. Be sure not to spray while the tree is in full bloom, as the insecticide may kill beneficial pollinators.