How to Protect Carrots from Carrot Fly

What is carrot fly?

If you have yet to experience that awful sinking feeling of lifting carrot after carrot riddled with dark crevices, tunnelled out by the dreaded carrot fly larvae, then consider yourself lucky. Carrot fly damage is no laughing matter.

What does a Carrot Fly look like?

The adult carrot fly is approximately 9mm long. It is a slender, metallic, greenish-black fly with yellow legs and head. Larvae are creamy white, tapering maggots.

Carrot fly lays their eggs in the soil around carrots.  Carrot fly eggs take only about a week to hatch. Once hatched the carrot fly maggots begin to eat their way into carrots leaving black holes. The black holes then become an invitation to diseases. 

Carrot fly also affects other vegetables in the parsley family, such as Parsnip, Celery, Dill, Coriander, Fennel and Celeriac.

Where do Carrot Flies Live?

Carrot Flies live in bushes, hedges, trees and thrive on allotments where members of the carrot family are planted close together year after year. The  carrot fly larvae that cause the damage live around the roots of the carrot plant.  They can continue to feed through the autumn into winter, moving between plants.

How do I know if my carrots have Carrot Flies?

The first symptoms are a reddening of the Carrot leaves, which start to wilt. they also lay their tiny cream eggs on the surface of the soil around carrot plants so look out for these - harder said than done when you are trying not to crush the leaves and attract carrot flies. 

If you miss these signs then the first you may know is when you pull your carrots up and find them full of holes.  

At what stage should I protect my carrots from carrot fly?

There is a lot you can do at the planting stage to ensure you get a healthy crop. There is no cure once the larvae are around the roots so carrot fly prevention is a

must. With other veg you can wait until they are ready to fruit to use plant protection. Carrots need carrot fly netting at an earlier stage and it’s no ordinary netting as carrot flies are tiny!  

One option is covering the carrots with a Fleece Blanket immediately after sowing. The other is by putting an ultra fine mesh like Micromesh Pest & Wind Barrier around them after the carrot seeds have been sown. As the carrot fly moves around at ground level the micromesh barrier is super-efficient at keeping the fly at bay as well as protecting your crop from harsh winds.

How do you protect carrots from carrot fly?

1. Make sure to avoid using previously infested ground. Carrot fly larvae can survive through the winter. So, rotate your crops and avoid re-sowing any vegetable from the Parsley family (see above)
2. Sow later to avoid sowing during the main egg-laying periods, the carrot root fly season in the Uk for most parts, is: mid-April to the end of May & Mid-July to the end of August.
3. Sow disease and pest resistant seed varieties such as Fly Away F1 and Resistafly F1, available from garden centres and online seed suppliers.  
4. Sow thinly to avoid ‘thinning out’. Thinning seedlings causes the leaves to bruise which emits the scent of carrots into the air which attracts the carrot fly. Thinning out is necessary as carrots crowd each other if not. This results in a crop of scrawny carrots.
5. Thin out or harvest on a dry evening with no wind – or use scissors so that no bruising of foliage occurs (which will release scent attracting the carrot-flies)
6. Try companion planting - we have been asked do marigolds deter carrot fly. The answer is Yes! Growing varieties of pungent Rosemary, Alliums, Sage or Marigold provides a deterrent/’smokescreen’ You could also try Garlic - see below.
7. Grow your carrots in a tall planters - for example the Carrot Patio Planters.  You could also try growing carrots in Raised Beds with Micromesh Cover as this may help deter carrot flies.   
   
8. Lift main carrot crops by Winter, especially if any are infected – don’t leave them in the ground to serve as food for overwintering larvae.
9. And lastly you may want to know can I eat carrots that have had carrot fly? The answer is yes but you may not find them to be worth the effort. They will be full of holes which you can cut away but you may find they are more hole than carrot!

How do you Treat Carrot Fly?

You can try nematodes to treat carrot flies.  The nematodes are microscopic and are watered into soil. The nematodes find and enter the Carrot Root Fly larvae, releasing a bacteria that kills them. The nematodes then use the body of the larvae to reproduce in, releasing more nematodes into the surrounding area. Carrot Root Fly nematodes will stay active in the soil for about 3-4 weeks. 

Garlic Spray for Carrots

You can also use a home made Garlic Spray to prevent Carrot Fly infestations.  This is more to disguise the smell of the carrots so that the carrot flies don't find them.  You could also try companion planting onions and garlic beside your carrots for a similar effect.   

To find out more about carrot fly, and the other pests that may arrive in your garden check out Pippa Greenwood's excellent RHS book for plant by plant advice on Pests and Diseases

Have you any experience of carrot fly damage? What do you think went wrong? Please let us know your thoughts using the comments section below.