Growing carrots at home can be fun and rewarding, but things don’t always go according to plan. Carrot fly is one issue you might encounter when growing carrots and other related plants in your garden.
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What is Carrot Fly?
Carrot fly is the name we give to a small black bodied fly called Psila rosae. It lays eggs in the soil of a garden, and when those eggs hatch, they reveal slender, creamy-yellow maggots that are a pest that can eat their way through carrot roots, rendering them inedible.
Carrots, in spite of the name carrot fly, are not the only crop that can be affected. Celery, celeriac, parsley and parsnips are all related and can all also be eaten by the carrot fly. So carrot flies are often considered to be a major pest in a vegetable garden. Be sure to integrate companion plants for carrots to help them grow better and aid alongside your carrot fly prevention efforts.
Carrot Fly Prevention
Carrot fly can be challenging to prevent entirely– especially if this is a problem prevalent in the area where you live and garden. Fortunately, however, there are a number of things you can do to prevent carrot fly from showing up in your garden in the first place.
While none of the strategies below will entirely prevent an infestation in all cases, they can certainly help to reduce the chances that this will become a problem in your garden.
Choose Resistant Varieties
First of all, it is important to understand that some varieties of carrots are far more resistant to carrot fly than others. Some have better resistance, however, they may still be bothered by these pests on occasion.
‘Fly Away’, ‘Maestro’, ‘Nantes 2′, Resistafly’ and ‘Sytan’ are five varieties that have better carrot fly resistance. But remember, this is not a complete panacea because these cultivars are less susceptible, but not entirely resistant to these pests.
Sow Carrots Later
An understanding of the lifecycle of carrot fly and the timings of their generations can also help you to keep carrot crops carrot fly free.
The carrot fly maggots hatch from eggs that are laid in late May or June, and then again from eggs that were laid in August or September. When they are just newly hatched, these larvae eat fine hair roots. Later, however, they bore into the top roots therefore competing with us for the parts that we like to eat.
Carrots that are sowed a little later – after the first generation of eggs in the late spring have been laid already – can potentially avoid an infestation. Harvesting carrots before late August can also keep carrots safe from the later generation.
Avoid Thinning Out
Thinning out carrots broadcasts their scent far and wide. So in order to avoid attracting carrot fly to your crops, and making the carrot location clear, keep things calm and quiet and let your carrots go unnoticed. Try to avoid the need to thin out your seedlings at all.
When sowing your seed, sow thinly, trying to keep a good spacing so that there will be enough space for the carrots to grow. If you must thin out, do so as quickly and gently as possible and try to avoid crushing the foliage or waving the plants around.
Keep Carrots as Healthy and Happy as Possible
Carrots that are as healthy and happy as possible are less likely to be impacted seriously by pests in general. When carrots are under threat, tor stressed, they will tend to give off more of their fragrance which can draw more pests in their direction.
To keep carrots happy, therefore, you should make sure that all of their environmental needs are met. Especially think about their needs when it comes to sunlight, water and soil as these are the things that are most important for plant health.
One important thing to remember is that for the overall and longterm health of your garden, you don’t want to prevent insects – even those considered pests – from entering your garden altogether. After all, this is not a hermetically sealed space and each insect plays its role within overall garden ecology.
The key is more to protect carrots, while tolerating pests as members of the biodiverse plant and animal communities around us.
Sometimes, however, learning about how to grow carrots in containers is the better way to prevent carrot flies from causing a nuisance.
Protection Tactics – Ways to Care for Carrots to Protect Against Carrot Fly Infestation
Some of the techniques that we might use to protect carrots and carrot fly prevention techniques involve the decisions we make in garden design, and how we care for our crop. To keep carrots safe we need to:
- Choose the Right Location
- Companion plant with beneficial companions
- Avoid bad companions.
- Practice Crop Rotation
- Utilise Netting and Barriers
Choose the Right Location for Carrots
A more exposed location might not always be ideal for growing vegetable crops. But somewhere with a good bit of breeze can actually be beneficial when growing carrots as it may help to keep carrot flies away. These flies don’t like wind, and will be able to travel more easily when it is very calm and still.
Another thing to think about when choosing where to grow carrots is that these insects will tend to fly only within a certain distance of the ground and not higher up. Growing in higher raised beds then may potentially help to keep the root crops safer than they would be at ground level.
Companion Planting to Protect Carrots from Carrot Fly
One of the best weapons that we have in our arsenals as organic growers to protect out crops is effective companion planting. Companion planting is not an exact science and there are many facets to plant interaction and many beliefs that science has not yet confirmed.
But many, myself included, agree that combining plants in the right ways can certainly help significantly in reducing pest problems and increasing yields from a vegetable garden.
In our attempts to protect carrots and other susceptible crops from carrot fly, the allium family are our greatest friends. Onions, garlic and other members of the same family make good companions because of their own strong smell.
They can mask the scent of carrots grown close by. Carrot flies are less likely to be attracted to the area to lay their eggs and so your carrots can often be kept safe.
I always companion plant carrots and onions of some kind in my garden. I do this when checking over when is harvest season in the UK.
Bad Companions for Carrots to Avoid
When thinking about where to place carrots it is important to think about other plants close by – including weeds that are in the same family and which may harbour carrot flies too.
You may also wish to avoid growing other susceptible crops too close to carrots. If you are growing susceptible crops in the same bed, it is important to make sure you create polycultures with plenty of other plants around, alongside and between them.
Crop Rotation to Reduce Carrot Fly Problems
Rotating crops is also important to reduce carrot fly problems since larvae can overwinter below the soil in a bed or other growing area. So we should avoid growing carrots or other susceptible crops in the same bed the following year.
One common plan involves creating a crop rotation with peas and beans, brassicas, potatoes and carrots and onions. A classic four year rotation plan of this kind can work very well and should help to prevent the build up of pests or disease.
Create Netting Barriers Around/ Over Your Carrots
Overall, the most effective way to protect carrots and other susceptible crops from carrot fly is covering the crop with a fine mesh netting, very well pegged down along all the edges. Some try barriers that are vertical, placed around the crop.
These do make tending the garden much easier. But unfortunately, barriers of this kind, though flies fly low, has not been shown to offer adequate protection.
Carrot Fly Prevention in a Polytunnel
Growing carrots or other susceptible crops in a domestic polytunnel or fruit cage can already provide a little more protection for plants than growing outdoors. But a polytunnel will need to be ventilated through opening side vents and/or doors. And so the polytunnel itself will not usually serve as a sufficient barrier between carrot flies and your crops.
Some strategies sometimes employed in polytunnels or greenhouses to manage pests are sticky traps, or broad-impact biological controls such as nematodes.
However, it is important to remember that both sticky traps and broad spectrum type nematode treatments also impact other soil insects, not just the carrot fly larvae.
And this can mean that you negatively impact creatures that you really want in your space, as well as those you don’t. It can potentially upset the natural balance in your garden. So it is best avoided.
You might consider specific and more targeted nematode treatments – though in my opinion these options of biological control should only be considered as a last resort. Nematodes recommended for severe carrot fly problems are Steinernema feltiae for spring, and Steinernema carpocapsae in the summer months.
How do I get rid of carrot fly?
To combat carrot fly:
Companion Planting: Plant onions, leeks, or garlic near carrots to deter the flies.
Barriers: Use fine mesh or fleece around the carrot crop to prevent the flies from reaching the plants.
Crop Rotation: Avoid planting carrots in the same spot year after year.
Sow Late: Delay sowing until early summer when the first generation of flies is less active.
Resistant Varieties: Opt for carrot varieties that are resistant to carrot fly.
What months do you get carrot fly?
Carrot flies are most active during their two main egg-laying periods: May to June and then again in August to September. These periods can vary slightly based on local climate conditions.
Can you eat carrots with carrot fly?
Yes, carrots with carrot fly damage can be eaten. The tunnels made by the larvae can be cut out, and the rest of the carrot is safe to consume. However, the damage can make the carrots less aesthetically pleasing and can sometimes cause them to rot if not used promptly.
How high do carrot flies fly?
Carrot flies typically fly at a height of up to 60 cm (about 2 feet) above the ground. This is why barriers of this height or slightly taller can be effective in preventing them from reaching the carrot plants.
Thompson & Morgan. (n.d.). Carrot Fly Free Seed Collection. [online] Available at: https://www.thompson-morgan.com/p/carrot-fly-free-seed-collection/4101TM [accessed 06/10/23]
Hillier. (n.d.). UK Garden Pests. [online] Available at: https://www.hillier.co.uk/garden-and-home-ideas/uk-garden-pests/ [accessed 06/10/23]
Elizabeth Waddington is a writer and green living consultant living in Scotland. Permaculture and sustainability are at the heart of everything she does, from designing gardens and farms around the world, to inspiring and facilitating positive change for small companies and individuals.
She also works on her own property, where she grows fruit and vegetables, keeps chickens and is working on the eco-renovation of an old stone barn.
To get in touch, visit https://ewspconsultancy.com.