Wednesday Wigglers ~ Carrot Root Fly

Whether you’re a gardener or not it’s likely you’ll have heard about carrot root fly, the curse of many a grower.

Although I’m aware of many cases where people have suffered this pesky little pest and read up on all the tips on how to avoid it, during the years I’ve been growing food myself I’ve never seen the damage the grubs cause until now.

The images below were taken in Callan community garden which saw its first infestation this year.

No wonder people give up growing carrots and parsnips…. arrrghh! It’s heartbreaking to patiently wait for your carrots to grow only to pull them and find them all eaten, black and maggoty.

There are however, ways of tricking the fly and/or learning to accept that this pest exists and work around its life-cycle without resorting to the use of chemicals.

But first of all a few facts about carrot root fly…

It’s a small fly that lays its eggs in the soil around the carrots (but can also be around parsnips, parsley and celery that are all related to carrots). The eggs hatch about a week later and the maggots begin to feed on the seedlings or roots. It takes around three months for the larvae to develop into mature adults.

The carrot root fly generally has two egg laying cycles – April to May and July to August though there can be three depending upon the weather.

The insect can survive through the winter in the soil in its pupal stage. The maggots can survive through the winter months on carrots left in the ground if the flies lay their eggs for a third cycle.

Eight tips to prevent carrot root fly destroying your crops…

1.  Check your roots to see if they’ve been infected. The first sign (but not always) might be a discolouration of the leaves where they show a red or purplish tinge. Pull the carrots (or other roots) out of the ground immediately you notice an infestation. The infected roots can be fed to animals but unless you have a very hot compost heap, avoid adding the infected carrots to it.

2. Look out for resistant varieties of seeds that will be clearly labelled such as Fly Away, Carrot Maestro and Flyfree. Note that resistant is just that, these seeds aren’t guaranteed to deter the fly if it takes a fancy to your seedlings.

3. The adult fly has a very strong sense of smell! Avoid sowing the seeds too thickly which will result in you having to thin most of them out, attracting the fly as soon as the foliage is bruised. When you do thin the carrots, try and do so on a dry still evening when the fly isn’t as active and again, harvest them in the evenings where possible.

4. Create a barrier around the bed, preferably using a very fine mesh or even plastic or cling film that the carrot root fly can’t get through. It should be at least 70 cm (over 2 ft high).

Alternatively plant the seeds into high raised beds or containers, again 70 cm high or over, or cover them with a cloche like the example here.

5. Carrot root fly doesn’t like the smell of onion leaves but to be very effective you’d need to sow a row or two of carrots between several rows of onions – three or four to one.

6. Grow undercover. The carrots grown outside in Callan were all infected by carrot root fly whereas all the carrots grown in the polytunnel remained untouched.

7. Crop rotation. Move crops around on a three or four-year rotation.

8. Garden Organic have an excellent tip about mulching around the carrots with a thick layer of grass clippings. Not only will it prevent the carrot root fly from laying her eggs in the soil, predators will hide and eat the larvae once they hatch.

Given that carrot root fly is so prolific, it’s likely that all varieties of carrots available in shops not labelled organic or chemical free will have been sprayed with pesticides to prevent it. Remember that next time you munch on a carrot straight out of the fridge without scrubbing it…

Have you any tips for preventing carrot root fly or have you given up growing carrots and roots altogether?