Waiting for the perfect time to pick ripened apples on the tree in your backyard is a test of patience. Finding white worms digging brown tunnels and crawling through your finally developed prized fruit is a test of sanity. When it comes to tiny white worms inside apples, the two most likely suspects are codling moths and apple maggots. You can control both of these pests in backyard trees without pesticides.
Adult codling moths have gray striped wings with a copper patch toward the outer ends. They are between 1/2 to 3/4 of an inch long and start appearing after the petals fall from the blooms. White larvae eat into the apple from the outside and grow up to 1/2 of an inch long, leaving brown trails as they eat. Control small populations by trapping adults on scented, sticky boards or balls so they can't lay eggs. Heavy infestations might require CYD-X or Spinosad, safe insecticides that do not effect people.
Apple maggots mature into a small, black fruit fly about 1/4 inch long that has dark stripes on transparent wings. They start appearing in mid-June, but the greatest numbers are seen in late July and early August. Eggs are laid under the apple skin, where several maggots grow to about 5/16 of an inch, leaving small winding tunnels as they eat. Scented, sticky traps are also the best way to control moderate numbers of apple maggots, but kaolin clay, an organic powder, will discourage egg laying.
Bagging apples on the tree will protect the fruit even from high populations of these pests, and others, without any insecticide, though it takes a lot of work. Staple or tie brown paper bags around the stem of young fruit about 3/4 of an inch in size or when the first pests are caught on traps. Remove any unbagged fruit from the tree. Leave the bags on until two weeks before harvest, so the apples can color in the sun.
Under the Tree
Both Codling moths and Apple maggots pupate in the soil after the damaged apples fall from the tree. The tiny white worms eat their way out of the fallen apples and crawl into the first few inches of the dirt. Cleaning up fallen apples as soon as possible is essential in breaking their life cycle. Additionally, allowing clover to grow under the tree can attract predators that feed on insect pupas.