Carrot Fly UK
Carrot fly (Psila rosae) larvae tunnel through carrot, parsnip, and parsley roots causing rusty scarring, rot, and inedible crops. Prevention is the only reliable strategy.
Pest control advice verified against RHS guidance by the SoilCommander Growing Team.
Life Cycle and Peak Risk
Carrot fly has two main generations in the UK: the first flights occur in May–June; the second, more damaging generation flies in August–September. The fly is a low-flier — it rarely rises above 60cm — which is why barrier fencing is so effective.
Prevention Methods
- 60cm barrier fence: erect fine mesh (0.8mm) or fleece on all four sides of the carrot bed at 60cm height; the fly cannot get over this height
- Cover crops entirely: fine insect mesh laid directly over crops from sowing to harvest is the simplest and most reliable method
- Thin in the evening: thinning releases volatile compounds that attract carrot fly; thinning at dusk and removing all thinnings from the site minimises risk
- Choose resistant varieties: Flyaway and Resistafly have partial resistance and suffer significantly less damage
- Companion plant with onions: the scent of alliums confuses carrot fly; interplanting rows of spring onions between carrots offers some deterrence
- Avoid later sowings: sowings made after June miss the first generation but are exposed to the damaging August–September generation; use mesh for all late sowings
Affected Crops
Carrots are the primary target but carrot fly also attacks parsnips, parsley (including Hamburg parsley), celery, celeriac, and other members of the Apiaceae family.
Common Mistakes to Avoid
- Using a barrier fence instead of complete covering. RHS research comparing barrier heights against full covers found complete covering more effective than a barrier alone.
- Skipping rotation because the bed is netted. Adult carrot flies can emerge from pupae already overwintering in that soil, inside the protected bed itself — netting doesn't replace rotation.
- Thinning at midday instead of dusk. Thinning releases scent that attracts egg-laying females; doing it at dusk and removing all thinnings immediately minimises the risk.
Frequently Asked Questions
Is a barrier fence as effective as full netting?
No — RHS trials comparing barrier heights with complete covers found a full cover more effective than any barrier fence alone.
Do I still need to rotate carrots if I use insect mesh?
Yes — carrot fly can emerge from pupae already overwintering in that same soil, inside the netted bed, so rotation still matters even under cover.
When is it safe to harvest carrots to dodge the worst carrot fly damage?
Harvesting before late August avoids the second, more damaging generation of the year.
See all pest and disease guides: Garden Problems UK · Growing carrots? See How to Grow Carrots UK · Browse sowing dates in the UK vegetable planting calendar
Last updated 4 July 2026
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.