Carrot Rust Fly

• Rusty-brown discolored tunnels running lengthwise through carrot and parsnip roots when pulled and sliced
• Stunted, yellowish carrot tops that wilt in the heat — the root is being consumed below ground
• Creamy-white maggots, about 1/3 inch long, found inside tunnels in the root when it is cut open
• Forked or distorted roots where larvae tunneled through early root tissue during development
• Entry wounds at the root shoulder covered by soil — damage is hidden until harvest or when tops yellow

The adult is a small, shiny black fly with a yellow head. Adults emerge in spring, coinciding with hawthorn bloom in many regions — a useful phenological cue. Females lay eggs at the base of carrot plants near the soil surface; larvae hatch and burrow down into the root. There are two to three generations per season in many regions: a spring generation, a midsummer generation, and sometimes a fall generation that overwinters as pupae in soil. The fall generation typically causes the most damage to roots stored in-ground over winter.

1. 01Cover carrot rows with fine insect mesh (0.8mm or finer) at sowing and keep covered through the season — this is the most reliable home-garden control method
2. 02Delay spring sowing by 4–6 weeks past your usual date to miss peak fly emergence, then use row cover on the late planting
3. 03Avoid growing carrots in the same bed in consecutive years; rotate with non-Apiaceae crops
4. 04Harvest spring-sown carrots before the second generation of flies lays eggs in midsummer
5. 05Do not leave carrot stumps or thinnings on the soil surface — they attract egg-laying females
6. 06Some gardeners have success planting carrots in beds away from hedgerows and weedy margins where adult flies overwinter

If row cover is in place and you're still finding significant root tunneling, your extension office can help determine whether the mesh gauge is fine enough and advise on regional fly pressure timing.

• Carrot Rust Fly— Oregon State University Extension
• Carrot Pest Management— University of Vermont Extension