Carrot fly (Psila rosae) is one of the most frustrating pests for UK vegetable growers. The larvae tunnel through roots, ruining crops that look perfectly healthy above ground. I switched to mesh covers years ago after one too many ruined harvests, and I haven't lost a carrot crop to it since. Prevention is far more effective than cure.
Founder & Head Grower, SoilCommander · RHS Level 2 · 12+ years growing in Yorkshire
I've been growing vegetables on my Yorkshire allotment and raised beds since 2012. Everything I write is based on what I've actually grown, failed at, and eventually got right in a real UK climate.
About Carrot Fly
The adult carrot fly is a small, shiny black fly about 8mm long. It lays eggs in the soil near carrot, parsnip, parsley, and celery plants. The creamy-white larvae hatch and tunnel into roots, leaving rusty-brown channels that make roots inedible and prone to rot.
Carrot Fly Attack Windows
| Generation | Flight Period | Crops at Risk |
|---|---|---|
| 1st generation | Late April – June | Early-sown carrots, parsnips |
| 2nd generation | July – September | Main-crop carrots, parsley, celery |
| 3rd generation (mild years) | October – November | Late carrots left in ground |
Identifying Carrot Fly Damage
- Foliage turns yellow or reddish and wilts despite adequate moisture.
- Rusty-brown tunnels and channels visible when roots are lifted.
- Small creamy-white maggots (up to 9mm) visible in damaged tissue.
- Roots rot quickly in storage if damaged — even minor tunnelling allows disease entry.
Prevention Methods
- Fine mesh or fleece barrier — the most reliable method. Cover rows with Enviromesh or fine insect mesh from sowing to harvest. Carrot fly cannot penetrate a well-sealed barrier.
- Vertical barrier — carrot fly flies low (below 60cm). A 60–75cm barrier of clear polythene around the bed deflects most flies; the RHS rates a 60–90cm barrier or insect-proof mesh as the most effective defence against this weak flyer.
- Sow late — delay sowing until late May or early June to miss the first generation flight peak.
- Harvest early — lift main-crop carrots before the second generation peaks in August–September.
- Grow resistant varieties — Flyaway, Resistafly, and Maestro have partial resistance to carrot fly.
- Avoid thinning in warm weather — the scent of crushed carrot foliage attracts egg-laying females. Thin in the evening and remove all thinnings immediately.
- Rotate crops — never grow carrots or parsnips in the same bed two years running.
- Companion planting — interplanting with onions or growing rosemary nearby may help mask the carrot scent.
Chemical Controls
There are no amateur chemical treatments approved specifically for carrot fly in the UK. Physical barriers remain the most effective and practical solution. Nematodes (Steinernema feltiae) can be watered in to target larvae in the soil, with some effect.
Plan your carrot sowing windows to avoid carrot fly with our UK Vegetable Garden Planner PDF — £19.
Frequently Asked Questions
Can I still eat carrots damaged by carrot fly?
Lightly damaged carrots can be eaten if the tunnelled sections are cut away and the carrot is used immediately. Heavily damaged roots rot quickly and should be discarded. Do not store any damaged carrots as the rot spreads.
Does carrot fly affect parsnips?
Yes. Carrot fly attacks all members of the carrot family (Apiaceae), including parsnips, parsley, celery, celeriac, and fennel. Use the same barrier and rotation strategies for all these crops.
How high does carrot fly fly?
Carrot fly typically flies below 60cm above the ground. A vertical barrier of that height around your carrot bed will deflect most flies, though it is less reliable than a full mesh cover over the crop.
When should I sow carrots to avoid carrot fly?
Sowing after late May misses the peak of the first generation flight. Harvesting before mid-August reduces exposure to the second generation. Combining late sowing with mesh cover gives the best protection.
Do companion plants really deter carrot fly?
Evidence is mixed. Interplanting with onions or strong-scented herbs like rosemary may help mask the carrot scent, but this is not reliable on its own. Use companion planting as a supplement to physical barriers, not a replacement.
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.
Plan the next step
Use the printable UK Vegetable Garden Planner to turn this guide into sowing dates, bed layouts, and weekly garden tasks.