Apple maggot is a common and easily transferred pest that can cause apples to be inedible and decimate entire orchards. It is now found in most of North America and can affect other tree fruits in addition to apples. Apple maggots tunnel into the flesh of the fruit, eating and laying eggs as they travel. They spend most of their life cycle protected in the fruit so insecticides focus on killing the adult flies that emerge from or land on the fruit. Apple maggots are distinguishable from other pests by their white headless and legless bodies. Quarantine and spraying are the major ways of controlling this problem.
Hang sticky traps with ammonia lures in your apple tree from late spring through the fall harvest. Use traps to catch and control the adult apple maggot flies if there are only a few or to alert you to a wider infestation that will require greater control measures such as insecticidal sprays. Use one trap for every 100 apples on your trees and hang them throughout the canopy on the outer 2/3 of the branches.
Use an organic preventative treatment by spraying your apple trees with a liquid kaolin clay product diluted with water according to label directions. Purchase your kaolin clay control products at the local garden center or nursery. Mix the liquid clay product and water in a horticultural sprayer and swirl or shake to combine. Spray the tree to entirely coat the the apples and leaves until they are dripping wet with the thin liquid material. Start this treatment in June, respraying every 7 to 14 days and more frequently if rain comes. Keep the apples coated with clay at all times as the film will deter flies from landing and laying eggs.
Spray the apple tree with an organophosphate insecticide containing malathion, carbaryl or esfenvalerate immediately after seeing an adult fly on the sticky trap. Wear a face respirator mask and eye goggles during application. Use the product straight from the commercially packaged sprayer or decant into a clean garden horticultural sprayer. Coat the branches, leaves, and fruit with the spray. Respray every 7 to 14 days until a few weeks before harvest and more often if it rains. Keep the sticky traps in place and if no new maggot flies are caught after three weeks time you can stop spraying.
Consult the label on your particular brand of organophosphate insecticide to ensure that you comply with the specific waiting interval between the last spraying and harvest time. This waiting period will vary widely by product ranging from a few days to two weeks or longer.