10 ways to avoid carrot root fly

Carrot fly is attracted to carrots by their scent. In spring the females emerge from hibernation to mate, before looking for somewhere to lay their eggs. They can detect the scent of carrots from a mile away and will make short work of your neat rows, laying their eggs in the surrounding soil, which then hatch into larvae that will burrow into the nearest roots.

While it's impossible to completely eradicate carrot fly, there are many ways to stop them taking hold. A healthy growing environment will ensure carrot fly affects only small amounts of carrots rather than the whole crop, while clever tricks like adjusting the timings of your sowings, erecting physical barriers and welcoming wildlife can also limit the amount of damage they cause. Find out more, below.

Choose resistant varieties

Choose varieties that have been bred for their resistance to carrot fly, such as 'Flyaway', 'Ibiza', 'Maestro', 'Parano', 'Resistafly' and 'Sytan'. These varieties aren't completely resistant to attack but are far less susceptible than others, so could be an option if your plot is particularly prone to them.

Avoid thinning out carrots

The process of thinning out carrots releases the wonderful carroty scent that attracts the egg-laying female carrot fly. By sowing thinly you reduce the need to thin out your crop after germination, and therefore the likelihood of a carrot fly finding your carrots.

Create physical barriers

Cover your carrot crop with horticultural fleece and secure this at the edges with pegs. This creates a physical barrier to the fly, ensuring she can't access the soil to lay her eggs.

Make fly barriers

Other physical barriers to carrot fly include growing your crop in a narrow beds surrounded by a 60cm-high barrier of polythene or fine-meshed netting. You can also create such barriers around pot-grown carrots, as pictured.

Use companion plants

Grow carrots alongside strong-smelling companion plants such as alliums, including chives and garlic. The scent of these plants will help to mask the fragrance of the carrots, which may stop carrot flies from finding them.

Avoid growing in long rows

Nature doesn't do monocultures, so neither should you. If you sow carrots in one long row then once a carrot fly has found a carrot she can quickly attack the rest of your crop, without much effort. By growing carrots among other vegetables you will thus make the scent of carrots harder to detect, but also make it harder for her to find other carrots to lay eggs around, so the percentage of carrots lost to carrot fly will be reduced.

Sow carrots later in the season

By changing the timings of your sowings you can avoid the main flying season of the carrot fly. Sowings made from June onwards tend to be less prone to attack than those sown earlier in the year, although bear in mind that a second generation of carrot fly is on the wing from July to September.

Practise crop rotation

Carrot fly overwinters as pupae in the soil. By practising good crop rotation you will ensure you don't grow carrots in the same spot in consecutive years, preventing last year's carrot fly from emerging in a new bed of carrots.

Avoid growing parsnips and celery

Parsnips, celery, parsley and celeriac also attract carrot fly, so avoid growing these crops near your carrots, as the fly will be able to detect them more easily and will also have an easy job to go from one crop to the next.

Be nice to moles

Many gardeners don't appreciate moles and even go to great lengths to try to remove them from their gardens. However, moles are soil-dwelling insectivores, which means they eat a number of soil-dwelling invertebrates. These include garden pests such as carrot fly but also leatherjackets, cockchafer larvae and even slugs. By being more tolerant of one species you will naturally reduce numbers of others you might consider 'pests'.

Caring for your carrots

Carrots don’t require a great deal of care. Try to keep the soil around them weed free, although once the carrots start to grow strongly their foliage will shade out most weeds. Water sparingly.