Carrot flies (Chamaepsila rosae) are unremarkable small black flies that lay their eggs in carrot crops. And you probably won’t notice the adults, because all the damage is done by their small creamy coloured maggots.

The maggots may munch at the seedlings as they come up or tunnel their way through the carrot roots, peppering it with small channels and holes. I find even when you cut out the bits with the holes, the tissue surrounding the damage has turned bitter. This is because the carrot reacts to try and ward off the pest.

When will I see carrot fly?

Carrot flies have two main egg laying periods, the first in mid-April, the second in June. In warmer areas of the country, there’ll also be a third period of egg laying in July-August. This third generation could affect carrots stored in the ground over winter.

Whether you’re affected by this pest, at your site, seems to be down to luck. Although some people suggest it may down to whether you have weeds that are in the carrot family in your vicinity. We know that if we don’t meticulously cover our carrots at Ryton in Warwickshire, they will be ruined by the pest. However, just down the road at Wellesbourne, we would be rewarded with perfect-looking carrots every time.

How to tackle carrot fly organically

Here are some of the suggestions for dealing with this pest organically. We have ranked them according to how effective we think they are:

Does work:

Sowing under fine mesh netting. Make sure you cover the crops immediately and use some water piping to make hoops to support the netting. Although unsightly, this is the bullet proof option.
Run a 50 cm barrier around your carrots. Our research has shown that few carrot flies are able to fly over this height, although some suggest it’s still not as effective as completely covering your crop.

Growing your carrots in a container that is more than 50cm high. This will keep away the carrot fly and make carrots easier to harvest.

Can reduce damage:

Sowing in late May but before the end of August to avoid the first and second generations of the fly. This is tricky to make work in practice, as changes in weather conditions can cause the patterns of egg-laying to shift, and sometimes generations of flies can even overlap.

Doesn’t work
Growing your carrots next to onions. This just doesn’t work against carrot fly sadly! To get any noticeable effect, you will need to grow a row of carrots with at least four rows of onions. However, we have found that this will only reduce the pest, not stop it.
Leather dust or leather dust mixed with paraffin. These are all things that Garden Organic/HDRA members have tried desperation against this pest. Don’t be tempted to try them as they don’t work!

For more advice about managing common pests the organic way, head to our Pest and Disease hub.