How To Keep This Pest Away From Your Carrots

The larvae of carrot rust flies can leave your beautiful, long, orange (or purple) carrots looking like a mangled mess.

by Jessica Walliser
PHOTO: Jessica Walliser/Flickr

Have you ever dug up your carrot crop only to find the roots riddled with tunnels and scars? Carrot rust flies may be to blame. This very small, shiny black fly has an orange head and legs, and while the adults don’t cause harm to carrots, their larvae certainly do.

Carrot rust flies overwinter in the garden and emerge in the spring. After breeding, female flies lay eggs near host crops, including carrots, parsnips, celeriac, parsley and celery,. The resulting larvae immediately burrow into the soil and begin feeding on the immature root, leaving tell-tale tunnels and scarring behind. As the root grows throughout the season, so does the carrot rust fly maggot, causing more severe damage as the summer progresses. Here are a few steps for managing carrot rust flies without resorting to chemical warfare.

1. Rotate Crops

Carrot rust flies are poor fliers and can’t travel far to find their host plants. Plant carrots and other susceptible crops in a new location every season. Try to choose a site that’s downwind of the location of last year’s crop. Carrot rust flies find their host plants by smell and prefer to fly upwind, so they’re less likely to discover your new carrot crop if it’s sited downwind.

2. Plant Around The Pest’s Lifecycle

Because the first generation of carrot rust flies emerges and begins to breed in April and early May in most parts of the country, delay planting your carrots until late May or early June. At this point, you’ll be between generations and will avoid any major damage. In parts of the country where a second generation occurs, breeding doesn’t take place until August and September.

3. Cover Your Plants

In order for female carrot rust flies to lay their eggs, they must have access to the host plants. Covering your carrot crop with a layer of floating row cover will keep the pests from doing any damage. Be sure to choose a summer-weight fabric and pin down or bury the edges to ensure this tiny fly can’t slip underneath to lay eggs.

4. Confuse The Female Flies

Because female carrot rust flies find their host plant via it’s smell, companion planting to mask the carrot plant’s distinctive fragrance may be helpful. This diversionary tactic works best if carrots are inter-planted with onions, garlic, chives, or other members of the onion family. Their strong scent helps “hide” the carrots from the egg-laying flies.

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5. Practice Good Carrot Hygiene

Discarded roots that are infested with carrot rust fly larvae often serve as overwintering sites for this pest. If you have a crop that’s been infested, don’t just toss the roots onto the compost pile where the larvae can continue to live. Instead, burn them, toss them in the garbage or bury them at least a foot deep. In many cases, carrot rust fly maggot damage can be cut out of the carrot, and the undamaged portion of the carrot can still be used in the kitchen.

6. Release Beneficials

Beneficial nematodes can be released into the soil near the carrot crop to help control the larvae. Species of nematodes in the genus Steinernema are most effective if applied in the spring according to the package instructions.

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