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Carrot Fly

Understand carrot fly and how to protect your crops from them

Carrot Fly

vegetables | grow your own

Adult Carrot Fly

Carrot fly (psila rosae) are the scourge of many vegetable growers rendering carrots, parsnips, parsley, and celery inedible. The female carrot fly lays eggs in cracks in the soil alongside crops from which maggots (larvae) emerge. Newly hatched maggots feed on the fine roots, but as they grow larger they bore into the tap root about half way down making tunnels as they eat their way through the carrot. With the carrots riddled with holes, they usually become rotten.

Carrot fly damage

Adult carrot flies emerge in May and June and start laying eggs alongside carrot plants just a few days later. Within 7-10 days the eggs hatch. The carrot fly maggots can grow up to 1cm long before transforming into the next generation of carrot fly. Two or three generations of carrot fly can occur through the spring and summer months before larvae or pupae overwinter in the soil to restart the cycle the following spring.

Since most of the damage to the crop occurs under the ground, the easiest way to detect carrot flies is that the foliage above the soil will become discoloured, wilted and droopy.

Preventing Carrot Fly

Thinning carrot seedlings attracts carrot fly

The simplest way to avoid carrot fly is to sow carrots late (at the end of May or in early June) so that the crops miss the first generation of the pest. If the carrots can be harvested before the end of August, then they are also likely to miss the second generation. Also, sow crops sparsely so that it is not necessary to thin the seedlings since when surplus plants are thinned out, female carrot flies are attracted to the strong smell released.

It is the maggots from the late summer generation which do the most damage, and the damage is worse the longer the crops are left in the ground.

Enviromesh fleece used to protect carrots from carrot fly

Since carrot flies do not fly more than 2 feet above the ground, vulnerable crops can be protected by surrounding them with a 2 foot high clear polythene or thin mesh barrier. Alternatively, a horticultural fleece can be used to completely cover the crops. (Note that it is essential to practice crop rotation when using these methods otherwise pupae which have spent the winter in the soil will attack the following years crop.)
If carrots are grown in containers with sides more than 2 feet high, then they should also be safe from attack.

Being such weak flyers, growing carrots at a windswept location is an advantage, however, weeding and thinning should still be done on a windless dry evening so that the carrot scent does not get to the carrot flies.

Carrot Fly Resistant Cultivars

Carrot seeds which are resistant to carrot fly

Some carrots have been bred to be less susceptible to carrot fly - such as Resistafly and Fly Away.

Article Published: 10:13, 5th Jul 2008

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