Apple maggot
Rhagoletis pomonella
15 host plants
Last updated
This profile synthesizes data from multiple published sources. Expert field review is in progress.
Apple maggot is a quarantine pest in Washington state. Western WA is within the quarantine area. In the Puget Sound lowlands, first emergence typically occurs in early to mid-July. Hawthorn hedgerows and abandoned apple trees in urban areas serve as significant reservoir populations. Home orchardists should monitor with yellow sticky traps beginning late June.
— Chris Welch, ISA Certified Arborist
Look for small dark flies with banded wings on serviceberry and native crabapple fruit in mid-summer (July through September). These flies lay eggs just beneath fruit skin. Inside infested fruit you will find translucent, legless maggots about 1/4 inch long that tunnel beneath skin, creating browning cavities and eventual fruit rot.
Hang yellow sticky traps near fruit in late June to monitor flies and reduce populations. Remove and destroy all fallen and rotten fruit throughout season; bury deeply or seal in containers to prevent emergence. Spray spinosad in mid-July and 10 days later when flies actively lay eggs. Mainly commercial issue; homeowners often accept minor fruit damage rather than spray.
Quick Reference
Apple maggot Emergence (est.) typically begins around 3060 GDD₃₂. As of April 24, 2026, Puget Sound stations range from 1455.1 to 1613.4 GDD₃₂, approximately 1447 units before the expected threshold.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 24, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,613 | Pre-season | Emergence (est.) | 1,447 |
| Seattle / UW | 1,574 | Pre-season | Emergence (est.) | 1,486 |
| Kent / Auburn | 1,559 | Pre-season | Emergence (est.) | 1,501 |
| Olympia / Tumwater | 1,524 | Pre-season | Emergence (est.) | 1,537 |
| Bellingham / Whatcom | 1,504 | Pre-season | Emergence (est.) | 1,556 |
| Tacoma / Puyallup | 1,492 | Pre-season | Emergence (est.) | 1,568 |
| Sequim / Rain Shadow | 1,455 | Pre-season | Emergence (est.) | 1,605 |
Source: MSU Extension: adults developmentally ready at ~900 GDD₅₀ (Jan 1 biofix). Peak emergence 1400-1700 GDD₅₀. UC Davis IPM phenology models: base 43.5°F, 1,129-1,456 DD emergence. Previous enrichment value of 638 GDD₅₀ was unsourced; CORRECTED 2026-03-20. Sources: MSU (MSU Extension), UC Davis IPM (UC Davis IPM), Wisconsin Extension (Wisconsin Extension). Updated 2026-04-03. About GDD₃₂ →
Monitoring & Action
Yellow sticky boards and red sphere traps (mimicking ripe fruit) hung at eye level in the outer canopy, one per dwarf tree or 2-4 per standard tree. Check traps weekly. Red sphere traps baited with apple volatile lures are most effective. Place traps by late June or 900 GDD50, whichever comes first.
One fly per trap per week warrants management action. In commercial settings, any trap catch triggers spray timing. In home orchards, low catches may be manageable with sanitation alone.
Females puncture apple skin to lay eggs, causing small brown dimples on the fruit surface. Larvae tunnel irregularly through the flesh, creating winding brown trails visible when the fruit is cut open. Tunnels are quickly colonized by decay organisms, causing soft brown rot. Heavily infested fruit becomes mushy and unmarketable. External symptoms may be subtle until fruit is cut: slight dimpling, premature drop, and soft spots. In Washington, apple maggot is a quarantine pest; transport of home-grown fruit from infested to non-infested areas is prohibited.
Cultural Controls
- Sanitation: collect and destroy dropped fruit
- Inspect fruit on the tree for dimpling and remove infested fruit
- Red sphere traps for population suppression
- Clean up all fruit at season end
- Plant less-susceptible cultivars