The worm problem you mention is most likely caused by coddling moth.
Controlling moths on apples in our area relies on an Integrated Pest Management (IPM) approach, combining cultural sanitation, physical barriers, and targeted, timing-sensitive insecticide applications to protect fruit from larvae that burrow into apples. The most effective method for both home and commercial growers is to use pheromone traps to identify the "biofix" (the first consistent flight of adult moths) and use that date to trigger control measures.
1. Monitoring (The Key to Timing)
Hang pheromone traps (delta or wing traps) in trees in March or early April, before the first bloom, to catch adult males. Monitor traps weekly. The "biofix" date is set when moths are consistently found in traps for two to three consecutive checks and evening temperatures exceed 62°F.
2. Cultural Control (Sanitation)
Scout weekly for "stings" (small holes filled with frass). Pick and destroy these fruits immediately—before the larvae exit—to prevent the next generation. Promptly remove dropped fruit from the ground. Thin apple clusters to a single fruit. Codling moth larvae often enter where two fruits touch. Wrap cardboard strips around the trunk in mid-June to trap larvae searching for a place to pupate. Remove and burn/destroy these bands in July, and again in October.
3. Physical Barrier
Bagging Fruit: This is highly effective for backyard growers. Bagging should be done 4–6 weeks after bloom, when fruit is 1/2 to 1 inch in diameter. Use paper lunch bags or nylon mesh bags to cover individual fruit.
4. Chemical and Biological Control
Timing: Sprays are ineffective once the larva has entered the fruit. Apply treatments at the start of egg hatch (about 250 degree-days after biofix, or roughly 17–21 days after bloom).
Codling Moth Granulosis Virus (CpGV): Sold as Cyd-X, this is a very selective virus that kills larvae. It requires frequent application (every 7–10 days).
Spinosad: Available as Entrust (organic) or Monterey Garden Insect Spray, applied every 10–14 days.
Kaolin Clay (Surround WP): A barrier spray that covers the fruit in a white film, deterring egg-laying.
Horticultural Oil: Used to smother eggs, often mixed with other treatments.
Monitoring usually starts in late April, with the first biofix often in early-to-mid-May. Eggs generally hatch in early June.