Carrot fly: damage, protection & prevention

Regina
Regina
Regina
Regina

I studied horticultural sciences at university and in my free time you can find me in my own patch of land, growing anything with roots. I am particularly passionate about self-sufficiency and seasonal food.

Favourite fruit: quince, cornelian cherry and blueberries
Favourite vegetables: peas, tomatoes and garlic

Carrot root flies can severely damage delicious carrot roots and also attack other members of the carrot family, otherwise known as umbellifers. Find out how to protect your crops against a carrot fly infestation.

Carrots eaten through by carrot flies
Carrot fly larvae feed on carrots, leaving behind little tunnels [Photo: Medvedeva Oxana/ Shutterstock.com]

Carrot flies (Psila rosae syn. Chamaepsila rosae) can wreak havoc in vegetable patches and lead to severe crop losses. As their name suggests, they are particularly fond of carrots (Daucus carota subsp. sativus). Read on to learn all about these destructive pests and find out when to look out for them as well as how to prevent and control them.

Carrot fly: profile and way of life

The first generation of carrot root flies hatch at the end of April from the overwintered pupae in last year’s carrot beds. These slender flies have red heads, black bodies and orange legs. After mating, the females go in search of suitable host plants. They like to infest all umbellifers (Apiaceae), so in addition to carrots, parsnips (Pastinaca sativa), celery (Apium graveolens), fennel (Foeniculum vulgare) dill (Anethum graveolens), chervil (Anthriscus cerefolium) and parsley (Petroselinum crispum) are also at risk.

Carrot flies are 5 to 6 mm large insects. They are not very capable flyers and usually only cover about 100 metres per day. This means that the carrot fly’s flight period extends over several days to weeks. Therefore, it takes until about the middle of May for carrot flies to find young carrots. Female carrot flies live for around four weeks and can lay up to 100 eggs during this time. To do this, they travel down the carrot plant and lay their eggs in the cracks in the soil around the root.

Carrot with brown tunnels from carrot fly larvae
Carrot fly larvae burrow their way into the carrot, leaving it susceptible to pathogens [Photo: Floki/ Shutterstock.com]

Carrot fly larvae are a creamy-white and up to 8 mm in size. They migrate into the soil after hatching and feed on the young, fine roots. Whilst the feeding damage by the first generation tends to be negligible, it can cause germinating or young carrot plants to perish. Carrot fly larvae pupate, hatch and lay the next carrot fly eggs in the soil a few weeks later. Usually, a second generation hatches from July onwards. Occasionally, a third generation will hatch in early autumn, though this is rare. These generations of carrots flies are the ones that start feeding on the inside of the carrot itself and cause the typical carrot fly feeding damage. Carrot fly larvae leave behind brown to black feeding tunnels in the middle to lower part of the carrot root. This renders some parts of the carrot inedible or unsuitable for use in the kitchen. These feeding tunnels are also later used as an entry point by other pathogens, which can sometimes cause root rot or storage rot.

Tip: If the feeding tunnels are more visible in the upper part of the roots, it is more likely you are dealing with carrot leaf miner flies (Napomyza carotae). In this case, there will be whitish feeding tunnels in the carrot foliage, which would not occur at all with carrot flies. Wireworms (Agriotes) also leave behind similar feeding damage, but their feeding tunnels are usually much larger and deeper. That said, wireworms infest carrots much less frequently than carrot flies.

Close-up of wireworms inside a carrot
Wireworms can cause a similar pattern of damage as carrot flies [Photo: Tomasz Klejdysz/ Shutterstock.com]

How to stop the carrot root fly

Nowadays, the use of chemical pesticides against carrot flies is no longer approved in home gardens. You can control a mild infestation by making sure your plants are strong and healthy. There are also lime-based products that are suitable for use in organic farming that you can apply while you are planting carrots to protect against carrot flies. Azadirachtin in the form of neem oil, a natural active ingredient from the seeds of the neem tree (Azadirachta indica), can also help to keep adult carrot flies off the leaves.

Orange and yellow sticky traps can help you to estimate when the carrot flies are in flight and can catch at least some of the adults before they lay eggs. Our Plantura Yellow Sticky Traps are non-toxic and safe for humans and pets. When using sticky traps outdoors, make sure you only place them in the immediate vicinity of your carrot plants. This will help prevent any other creatures (including beneficial insects) from accidentally getting caught in them. Sticky traps also indicate at what point you should use crop protection nets. At the latest, you should use these nets when you notice the first carrot flies on your yellow sticky traps. There is no way of controlling carrot fly larvae once they have spread within the crop, so preventing a carrot fly infestation is the best method of control.

Yellow Sticky Traps 20-pack
Yellow Sticky Traps 20-pack
  • For detecting infestations early on and monitoring pest populations
  • 20 double-sided yellow sticky traps (or 40 smaller traps) to hang from plants or stick straight into soil
  • Odourless & insecticide-free

How to prevent carrot flies

There are several ways to prevent a carrot fly infestation. When harvesting umbellifers, remove everything from the bed including foliage, any root remains and other harvest residues. Due to their distinctive smell, these attract carrot flies and give them somewhere to overwinter. Find more tips on how to harvest and store carrots in our separate article.

Carrot fly-resistant varieties

Planting the right carrot variety can prevent carrot fly infestations in the first place. Suitable carrots include early-maturing, fast-growing varieties such as ′Nantaise 2/ Milan′ which can be harvested from June onwards and therefore avoid being munched on by the carrot fly larvae later on. Tolerant and resistant varieties are also suitable and can be sown later on in the year. These are seldom to never attacked by carrot flies. ‘Ingot F1’, ‘Resistafly F1’ and ‘Flyaway F1’ are some noteworthy robust hybrid varieties.

A mixed culture garden with carrots and onions
Planting alliums near your umbellifers can help keep carrot flies away

Crop rotation and companion planting

Crop rotation is an effective way of preventing many pests and diseases. Avoid growing carrots and other umbellifers straight after each other on the same plot. Taking a cultivation break of four years between umbellifers prevents not only carrot flies, but also other carrot diseases such as carrot leaf blight (Alternaria) or stem rot (Sclerotinia sclerotiorum). Planting carrots together with alliums (Allioideae) such as onions (Allium cepa), garlic (Allium sativum) or leek (Allium porrum) also keeps carrot flies away thanks to the smell they emit. This type of companion planting also benefits alliums, as onion flies (Delia antiqua) cannot stand the smell of umbellifers.

Where you plant your carrots also plays an important role. Carrot flies only travel short distances, so are limited to one area and prefer windless locations. It is hard for them to spread to carrot crops in windy spots.

Carrot fly netting

Crop protection nets are great for preventing carrot root fly infestations. Nets with a mesh size of 1.35mm x 1.35mm or smaller act as a successful barrier to stop carrot root flies from getting to your carrot crops. If you would also like to prevent carrot leaf miner flies, use nets with mesh sizes less than 1mm.

Carrots growing beneath protective net
A crop protection net is very effective against carrot flies [Photo: Steve Cymro/ Shutterstock.com]

Spread the net over your carrots in early May, using a wire frame, for instance, to hold it up. This prevents the nets from exerting any pressure on the plants even when it rains. Make sure the net is in contact with the ground at the edges and secure it with stones or boards so that there are no gaps through which the carrot flies can enter. You can remove the carrot fly netting about three to four weeks before harvesting your carrots. At this stage, an infestation would only affect the fine roots, but the carrot flies would not cause any damage to the actual roots.

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