How to Identify, Control, and Prevent Carrot Fly

Some of my favorite things to grow are root vegetables because of their element of surprise. Those that grow underground hold a sense of mystery. Only their foliage gives some indication of what’s below the surface.

But I’ve also encountered some unpleasant surprises, including the damage of the carrot fly (and discarding substantial parts of my carrot harvest due to this pest). 

The carrot fly is a common pest for over 100 umbelliferous plants. Plants that are in the carrot family (not just carrots) such as celery, celeriac, and parsnips are also susceptible to carrot fly attack. Flies can also sustain themselves on weed species such as the wild carrot. 

The carrot root fly is one of the most economically damaging carrot pests. As with many other pests, the carrot fly larvae cause the most damage to crops. Although they aren’t as common in urban areas, they are still a concern to watch out for in gardens.

What is Carrot Fly?

The carrot fly, Chamaepsila rosae (formerly known as Psila rosae) is a pest found throughout temperate regions of the world. It is also commonly called the carrot rust fly for the rust-colored frass or excrement the larvae leave behind as they tunnel through the roots. Not only do the tunnels themselves make the vegetable unsightly, but they also encourage secondary rot.

Adults are around 6-8mm long with a shiny black abdomen and thorax, an orange head, and yellow legs. Female flies have abdomens that end in a pointed tip as opposed to the curved shape of male flies.

Both males and females have dark transparent wings and typically fly no more than 18 inches above the ground. The eggs of the carrot rust fly are white and oval-shaped. The larvae are small and yellow. 

Life Cycle

Depending on temperature and climate conditions, there may be one to three generations of carrot flies per year. They overwinter in the soil and emerge from their pupal stage in May and June. They then mate and the female carrot flies will lay clusters of eggs on the soil surface near their host plants.

Carrot flies are directed to their hosts by sight and smell. Each female can lay around 40 eggs in her lifetime. Eggs hatch into larvae within six to ten days and begin tunneling and eating through the root. It takes approximately 25 days for the larvae to pupate and start the cycle again. 

Common Habitats

Overwintering pupae emerge as first-generation adult flies in early spring from the soil near susceptible hosts. Low-flying female flies can be found near a host plant, typically no more than 18 inches off the ground.

These flies lay their eggs just under the surface and young larvae are found inside the root surface. Many carrot-growing regions experience at least two generations. 

What Do Carrot Flies Eat?

Carrot flies typically eat the roots of umbelliferous plants. Larvae damage is typically found on the bottom part of carrot roots but on the top or shoulder of parsnips. As larvae mature, the amount of damage they cause also increases. When there is a large infestation in an area, these flies may also impact the lower stems of celery plants.

Since there might be multiple generations per year, the overall damage compounds over the course of the growing season, starting with the smaller spring generation. 

How to Control Carrot Flies

Despite their name, carrot rust flies can feed on many other host plants and are not carrot specialists. Their range of foods makes them difficult to control because they are not dependent on one. In fact, many market farmers who grow a range of different vulnerable crops have stopped growing carrots because they have not been able to find a cost-effective way to control this pest for their carrot crop.

Because of the economic importance of carrots, there are ongoing research efforts to study integrated pest management techniques, companion planting, crop rotation, using floating row covers, and more. 

Organic or Chemical Control

Insecticides are difficult to use with carrot flies because of this pest’s behavior. Adults do not linger near their hosts after laying eggs and their larvae are found underground.

Pyrethroids are not effective against eggs or larvae but can decrease the adult fly population through broadcast spraying, which is not an ideal control method. 

Environmental Control

Place yellow sticky traps near carrots and other hosts to monitor the adult population. However, note that these will affect all insects – not just carrot flies. Row covers are effective on a small scale because they provide a physical barrier to prevent adult flies from laying eggs near susceptible crops.

The effectiveness of row covers depends on them being firmly secured around these plants as soon as seedlings emerge before the adult fly population peaks in mid-June.

Crop rotation can be effective on a larger scale with at least 1000 meters separating the previous plot of carrots and future carrots. The distance required means this method is most likely only applicable to farmers instead of home gardeners. 

Adult flies identify their hosts through sight and smell. There have been studies that recommend intercropping carrots with a non-host crop to confound the flies. Some studies have shown that alfalfa could be a good option for companion planting as it also increases the number of predatory insects that can help manage the fly population. 

Prevention

Timing the planting of carrot seeds can have an impact on carrot flies. Since the first generation of flies are active in May and June, delay sowing carrots until after the first generation has died. Without an adequate food source for their first eggs, you will limit the size of the second generation. 

Where you plant these crops can also impact the number of carrot rust flies. Because this pest is a weak flier with limited vertical range, plant affected crops in an elevated planter at least 18 inches off the ground. Carrots planted in exposed areas with heavy winds also see less damage, likely because these flies are not able to lay eggs.

There are currently several carrot rust fly-resistant varieties such as Flyway and Sytan. It’s best to plant a non-resistant carrot bed next to resistant ones to serve as trap plants for this pest. 

Frequently Asked Questions