How to Prevent Carrot Fly From Destroying Your Crop

, written by Ann Marie Hendry gb flag

Carrot fly maggot

Recently I experienced one of the most disheartening crop failures a gardener can suffer. I noticed that some of my carrots had developed bronze foliage, so I pulled a few to see what was up. I dug up carrot after carrot, feeling more and more dismayed as I discovered that every single root was riddled with rusty and blackened tunnels.

I was sure that I knew what was responsible for the damage, but just to confirm I broke two or three carrots in half. Each root was honeycombed with tunnels, from which several drowsy, yellowish maggots wiggled.

My worst fears were confirmed: it was carrot fly.


The Curse of the Carrot Fly

Carrot flies themselves don’t cause any damage, but they lay their eggs near carrots and other susceptible crops such as parsnips, celery, dill and parsley. The ravenous larvae then wriggle down through the soil to the nearest available root – and begin to feed.

At first they may only nibble on the fine root hairs, but they soon progress to the roots themselves. They munch higgledy paths on the surface of the roots before boring into the heart of the carrot. This doesn’t usually kill the plant, but it can stunt growth and cause the bronze foliage I’d noticed. And, of course, depending on the extent of the damage, the roots become inedible.

Carrot flies produce two, and sometimes three generations per year. The first eggs are laid in late spring. These were the ones that hatched into the maggots that took a fancy to my carrots. Had I not interrupted the growth cycle by hoicking out the infested roots, they would then pupate and hatch into adult flies, ready to spawn a second generation.


How to Deter Carrot Fly

Carrot fly is a widespread problem, and gardeners and farmers have developed a range of techniques to deter them.

Companion planting. Completely encircling your carrot crop with allium family plants such as onions, leeks or chives is believed to literally throw carrot fly off the scent. As with most companion planting advice there is conflicting evidence on its effectiveness, so it’s worth experimenting in your own garden.

Strategic sowing times. Carrot flies are active from late spring until autumn. By delaying sowing until early summer, you can sidestep the first generation of the pest. My mistake this year was sowing too soon in my eagerness to get growing!

Avoid thinning. The process of thinning out carrots bruises the foliage and intensifies its scent, which is said to attract carrot flies from some distance away. Sow sparsely instead, so that thinning is not required.


Harvest susceptible crops promptly. In milder areas maincrop carrots can often be left in the ground over winter, but if your garden is prone to carrot fly lift them all in autumn. After an infestation turn the soil over occasionally – this will make it easier for birds to snap up overwintering larvae and pupae.

Crop rotation. Avoid growing carrots in the same spot every year. While this won’t stop carrot flies from flying in afresh each year to lay their eggs, it will avoid the risk of overwintering pupae emerging right in the middle of your crop.

Vertical fences. Carrot flies are low-flying insects, so a vertical barrier of horticultural fleece, fine mesh or polythene that is 90cm (3 feet) high should, in theory, stop them in their tracks. But – and there’s always a but – carrot flies are tiny, lightweight creatures which, even on a calm day, are bound to be buffeted around and lifted up over obstacles by the breeze. If you do try vertical barriers, make your carrot bed long and narrow to make it harder for the flies to land within them.

Grow in containers. Similarly, tall containers or high raised beds may help to reduce the incidence of carrot fly, but aren’t guaranteed to keep them away. If you grow containers of carrots on a second floor balcony however you may never see this pest!

Resistant varieties. There are some resistant varieties of carrot available – for instance, ‘Flyaway’ (which came out tops in Which? Gardening trials), ‘Resistafly’, ‘Maestro’ and ‘Parano’. Remember, they are merely resistant to fly attacks, not immune, so use these varieties in conjunction with other techniques.

The Only Surefire Way to Prevent Carrot Fly

The only guaranteed way to prevent carrot fly is to stop them from getting anywhere close to your carrots and other susceptible crops. In practice, this means draping row covers of horticultural fleece or very fine insect-proof netting over your carrots, either directly on top of the crop or suspended on hoops of wire or plastic. This must be done as soon as the crop is sown, and should only be removed very briefly to weed and harvest. Make sure to secure the edges of the cover so there are no gaps. Ideally, dig the edges 5cm (2in) into the soil.


Pest attacks are always disheartening, none more so than when they completely ruin the crop you’ve been so looking forward to harvesting and eating. But with good pest prevention techniques, carrot fly will soon be a thing of the past in my garden – and hopefully yours, too.

Don’t forget to report any carrot fly – or any other pests you see – to the Big Bug Hunt and help us to develop a pest prediction service so you can take action to protect your crops before pests strike.

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Show Comments


"How do farmers and commercial growers prevent damage by carrot fly. Surely they must use some kind of chemical treatment. Carrots in shops are always clean as a whistle."
James Taylor on Saturday 31 March 2018
"Hi James. Some areas are less affected by carrot fly than others, and some farmers will use row covers to prevent them, while others will unfortunately resort to pesticides. But a big reason the carrots in shops look so good is because any that are less than perfect are discarded before they get anywhere near the shop floor. Wastage of fresh produce that may be slightly blemished (or even just not perfectly shaped) is a major issue for farmers supplying supermarkets."
Ann Marie Hendry on Tuesday 3 April 2018
"This is a helpful post in all but one way - you give the height that carrot fly will get to as 36cm (3 feet). Presumably you mean either 36 inches which is 3 feet approximately, or 36cm which is 1 foot ..... which is it meant to be? Many thanks "
Devon Maid on Monday 28 January 2019
"Whoops - thanks Devon. We've fixed this now. "
Ann Marie Hendry on Tuesday 29 January 2019
"I was allways taught to only thin carrots when it is raining,it works for me in Staffordshire, or have I been lucky"
phil on Wednesday 27 March 2019
"Excellent and scary post, as it highlights one more thing I forgot existed. Thanks for covering a more permaculturally proper method of dealing with them. Using different crops in the guild, and avoiding monocrops is sure one way to start. Hopefully people are realising the polluting and toxic (to everyone, animals, soil and groundwater (nitrates)) effects of using chemically derived and manmade pesticides."
Marlon van der Linde on Thursday 26 September 2019
"Glad you enjoyed it Marlon! I do think more people are starting to realise that throwing pesticides at a problem isn't effective in the long term, as well as being harmful now and in the future."
Ann Marie Hendry on Wednesday 2 October 2019
"I sow my carrots each year in straight rows, weed, over looks good . result carrots like pencils. My neighbour just throws seeds down rakes in little weeding ...results perfect carrots. Therefore the local supermarket will continue supplying me with their carrots....Shame"
David on Wednesday 15 January 2020
"Carrots can be finicky David, but don't lose heart! Light, uncompacted soil (ideally sandy soil) and plenty of water will help them to produce chunky roots. And perhaps ask your neighbour what variety he's growing!"
Ann Marie Hendry on Sunday 19 January 2020
"Hi I sow my carrots under frames 2feet high and covered with veggie mesh and put grass clippings 2inches deep round the sides. I read somewhere that the carrot root fly doesn’t appear till about after 7am so I get up at 5 am to weed and thin and have the frames back in place by 6.30 It seems to be working but I would like to know without getting up at the crack of dawn the best time to harvest a few at a time as it takes a bit of effort to get the frames back in place as the plants are now quite tall."
Margaret Miller on Wednesday 15 July 2020
"Wow Margaret, 5am - that's showing some serious dedication to your carrots! I don't go to such lengths but just try to make sure covers are off for the minimum amount of time possible and replace promptly when I'm done weeding or harvesting. Using a low-nutrient mulch such as leafmould or shredded bark between the rows will help keep weeds down and minimise the amount of times you need to remove covers for weeding. Also, if you sow thinly you shouldn't need to pull out excess seedlings too often. It's not a perfect system, but it can work well."
Ann Marie Hendry on Friday 17 July 2020

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