Plant Problem Diagnostic
Codling Moth vs. Apple Maggot: Telling Them Apart and Controlling Them
The short answer
If the tunnel runs to the core and is packed with reddish-brown crumbly droppings (frass) and there is a frass-rimmed entry hole, that is codling moth. If the outside of the apple shows minute dimples or pinpricks and the inside has brown, winding trails threading through the flesh (not just the core) that break down into rot, that is apple maggot.
The most reliable home control for both is a physical barrier: bag individual fruit. UC IPM says to bag when fruit is 1/2 to 1 inch across (about four to six weeks after bloom), thinning to one fruit per cluster first. Wisconsin Extension recommends plastic bags stapled around the stem for apple maggot. Sanitation is the other pillar: rake up and destroy dropped fruit as soon as it falls.
Traps differ by pest. Codling moth is monitored with pheromone (delta/wing) traps to time any spray; apple maggot is trapped with red sticky spheres hung by late June to early July (Wisconsin advises one trap in a small tree up to six to eight in a large tree). Apply insecticides only on the timing your state Extension specifies, since it is degree-day or trap-driven and region-specific.
Which pest do you have?
Cut a damaged apple open. Codling moth larvae, per UC IPM, penetrate into the fruit and tunnel to the core, leaving holes in the fruit that are filled with reddish-brown, crumbly droppings called frass, with tiny mounds of that debris at the entry point on the surface. The damage is concentrated in a clean tunnel driving toward the seeds.
Apple maggot looks different inside and out. Wisconsin Horticulture describes the adult fly laying eggs that leave the surface sunken and darkened (minute dimples), while the larvae make slender darkened trails throughout the fruit, unlike codling moths that feed primarily in the core, until eventually the entire fruit becomes rotten. So: frass-packed tunnel to the core equals codling moth; dimpled skin plus brown meandering trails through the flesh equals apple maggot.
Bagging and sanitation: the home-grower core
Bagging physically blocks egg-laying and is the single most effective low-spray tactic for both pests. For codling moth, UC IPM says to begin bagging when the fruit is from 1/2 to 1 inch in diameter (four to six weeks after bloom): thin the fruit to one per cluster, slip each thinned fruit through a 2-inch slit in the bottom fold of a standard lunch bag so it seals around the stem, staple the open end shut, and remove bags just as fruit begins ripening. For apple maggot, Wisconsin Horticulture advises protecting developing apples by bagging them when they are young using sandwich-size plastic bags with the opening stapled shut tightly around the fruit stem.
Sanitation starves both pests of a next generation. UC IPM says to rake up and destroy dropped fruit as soon as it falls, especially in May and June, and to check trees for infested fruit every week or two starting six weeks after bloom. Wisconsin echoes this for apple maggot: dropped apples should be picked up very soon after dropping and destroyed or deeply buried so the insects cannot complete their life cycle, and nearby unmanaged apple trees should be removed where possible.
Traps and spray timing (per Extension)
The two pests use different traps because they are timed differently. Codling moth is monitored with pheromone-baited delta or wing traps, which catch males and tell you when to expect egg hatch. Apple maggot is caught on red sticky spheres that mimic ripe fruit: Wisconsin Horticulture recommends one trap in a small tree (under 8 ft), two to four in a medium tree, and six to eight in a large tree, hung as flies begin emerging at the end of June or early July, with dead insects cleaned off and fresh sticky coating reapplied every couple of weeks.
On insecticides, follow your Extension's timing rather than a calendar. For codling moth, UC IPM ties sprays to degree-days, starting as soon as calculations indicate eggs are hatching (250 to 300 degree-days after moths are caught in traps) or as soon as you see stings. For apple maggot, Wisconsin advises applications tied to fly emergence, roughly the first week of July with follow-ups about two weeks apart, each giving about two weeks of control. Any in-season insecticide belongs after petal fall, never during bloom; see the backyard fruit tree spray schedule for the full framework.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- UC IPM - Codling Moth Pest Note (7412) — Codling moth larvae tunnel to the core leaving holes filled with reddish-brown crumbly frass; bag fruit when it is 1/2 to 1 inch in diameter (4-6 weeks after bloom), thinning to one per cluster, using a lunch bag with a 2-inch slit and removing bags at ripening; rake up and destroy dropped fruit as soon as it falls, especially May and June; monitor with pheromone traps; start insecticides when degree-days (250-300 after first trap catch) indicate egg hatch or when stings appear.
- University of Wisconsin Horticulture Extension - Apple Maggot: Scourge of Home Apple Production — Egg-laying leaves the surface sunken and darkened (dimples); larvae make slender darkened trails throughout the fruit unlike codling moths that feed in the core, until the whole fruit rots; adults emerge end of June or early July into September; use red sticky spheres, one in a small tree (<8 ft), 2-4 in a medium tree, 6-8 in a large tree, cleaning and re-coating every couple weeks; pick up dropped apples soon and destroy or bury them; bag young apples in stapled sandwich bags; apply insecticides 2-3 times in summer about 2 weeks apart starting early July.
- WSU Extension - Codling Moth Versus Apple Maggot (Homeowner) — Codling moth damage is a hole filled with frass and a tunnel to the core with fresh holes in May/June and again at harvest; apple maggot damage is a frass-free hole with meandering tunnels that may fill with bacterial rot, with fresh holes appearing only at harvest.