Carrot Fly: Prevent Rusty Tunnels in Your Carrots
On this page
Rusty tunnels in the roots
The tunnels turn rusty brown and the roots can rot; young plants can be killed outright. Often you only find out at harvest, when a perfect-looking carrot is riddled inside.
A small fly with a good nose
The adult is a small black-bodied fly. There are two or three generations a year, and it overwinters in the soil as larvae or pupae. Thinning releases a carrot smell that attracts egg-laying females, so sow thinly to keep thinning to a minimum.
Keep them out
Covering the crop with fine mesh or row cover keeps the flies off. Rotate the bed, or flies that overwintered in the soil will emerge under the cover.
Sow to miss them
Sowing or harvesting so the crop misses the main egg-laying periods avoids much of the damage. Some varieties are less susceptible, though none is fully resistant. Growing guides: carrots and parsnips.
Related problems: cabbage caterpillars, seeds not germinating, soil problems. Or go back to all garden problems.
Carrot fly questions
Is there a resistant carrot?
Some varieties are less susceptible, but none is fully resistant, so cover the crop as well.
Which other crops does it attack?
Parsnips, celery, celeriac and parsley as well as carrots.
Regional notes
The problem is the same on both sides of the Atlantic; local advice and timing differ. Trusted local guides for this page:
- UK: RHS: Carrot fly. Timing in your area: the UK vegetable planting calendar.
- USA: Utah State University Extension: Carrot rust fly; UC IPM (University of California): Carrot rust fly. Timing in your area: the USA vegetable planting calendar.
- Canada: your provincial agriculture department, or Canadian university gardening services. Timing in your area: the Canada vegetable planting calendar.
More problems: all garden problems.
Sources and further reading
- RHS: Carrot fly
- Utah State University Extension: Carrot rust fly
- UC IPM (University of California): Carrot rust fly
Facts on this page are summarised in our own words from the pages above; each is supported by at least two of them, or by one plus well-established growing science (noted in our research file). Every source was opened and checked on 23 October 2026.
Keep a garden record
Most problems come back to the same beds in the same weeks. A simple record of what grew where, and when trouble started, lets you get ahead of it next year. Sketch your beds in the free Vegetable Garden Layout Planner Tool, and keep sowing dates, problems and harvests in the Global Vegetable Garden Planner (printable PDF). Every crop we cover is in the vegetable growing guides.
Last reviewed:
Fix The Cause, Then Plan The Next Crop
Troubleshooting works best when you improve the growing conditions and record what changed for the next season.
Keep going
Plan the next step
Use the printable SoilCommander planner for your region to turn this guide into sowing dates, bed layouts and weekly garden tasks.