Don’t you hate it when you have lovingly taken care of vegetables like carrots, but when you harvest them, they’re damaged by pests? All that growing work is wasted because now you can’t use them for anything.
Carrot flies are one such pest. They attack plants in the Umbelliferae, also known as Apiaceae, family. This includes carrots, parsnips, celery, and dill.
You can keep carrot flies out of the garden with a few steps at the right stage in their life cycle. Let’s start by getting to know these pests.
What Are Carrot Flies?
Carrot flies (Chamaepsila rosae, previously called Psila rosae) are tiny black flies whose larvae attack umbellifers by boring and eating their way through the root.
In addition to the plants mentioned above, parsley, fennel, lovage, cumin, and cecily are all at risk.
Once present, this destructive pest can destroy 90% of your crop, if not more.
The adult fly is about a fifth of an inch long. They have yellow legs and a red head on a black abdomen and thorax. Adult males have a rounded abdominal tip, and the females have a pointed one. The wings are either clear, like gossamer, or dark but clear.
The larvae are also about a fifth of an inch long and look like a tiny yellow-brown maggot.
Carrot flies are sometimes known as carrot root flies.
The Life Cycle of Carrot Flies
You should have an idea of the life cycle of carrot flies so that if you see any signs, you can decide what to do. Although they are known to infest other umbellifers, carrots are usually the main target.
Eggs
The adult carrot fly lays eggs at the base of the seedling on the soil or in the small crevices in the soil surface. This is in spring, typically around mid-May to mid-June. This timing may vary depending on where and when you sow seeds or transfer the seedlings.
The female will lay up to 40 eggs in clusters of three. She does this so that there is a chance that some eggs will hatch and survive if something happens to others. The larvae hatch in about one week.
Larvae
The young larvae burrow into the soil and initially feed on the thin, tender feeder roots at the base of the plant. Then, they move into the main root, where they will feed for around two weeks.
This is where the life cycle ends if you dig the carrot up. You will immediately know if carrot fly larvae have been feeding on your carrots.
If, after four to six weeks, the carrot hasn’t been harvested, the larvae will mature and leave the carrot root and pupate in the soil.
Depending on timing, the larvae can overwinter in the crop if it is left in the ground.
Pupae
The pupae remain in the soil until around mid-August to mid-September. It will emerge as an adult and lay the next lot of eggs.
You can get three generations in one season if the conditions are right and the crop is in the ground long enough.
The pupae will overwinter in the soil until the next year, when the cycle starts again.
Adult
The adult can also overwinter by sheltering in warm, dry areas, though this is less common. They generally live for up to four weeks. In that time, the female will lay her 100 or so eggs.
Identifying Carrot Fly Damage
Although the damage is confirmed when you dig up the carrot or harvest the vegetable, there are some signs to look out for on the aboveground plant.
Wilting
When larvae feed on the roots, otherwise healthy plants will suddenly wilt, despite sufficient water and nutrients. This can be confusing as you can’t see the damage being done under the soil’s surface. Eventually, the foliage yellows and dies or looks sickly.
Stunting
This is usually the first indication of this pest. Unfortunately, it can be difficult to spot, especially for the novice gardener. Unless you know the growth rate of the foliage, you may not even notice.
You generally don’t see adults flying around because they are so small. They don’t often fly higher than three feet, and they don’t fly far.
On the Root
The larvae bore tunnels in the lower part of the root. These tunnels become infected with bacteria and often turn smelly and mushy. In parsnips, they bore into the upper half of the root.
In both roots, the tunnels could be black or red. When you cut an infested carrot or other root open, you will likely see the yellow maggot-like larvae wiggling around.
10 Ways to Prevent Carrot Flies
There are various ways to prevent carrot flies, and most are cultural modifications. Timing is key, as well as understanding the pest’s life cycle.
1. Sow Later
In most areas, the first generation of the carrot fly season starts in mid-May to mid-September. This first flush of egg laying is usually the peak of numbers. Sow in mid-June, and you may have missed the adults looking for plants to lay eggs near.
Of course, there are subsequent generations, but given the worst egg-laying period is over, any subsequent flies won’t cause as much damage. The first generation is key to avoid.
This will delay your harvest, but it shouldn’t be a concern in most areas.
2. Plant Resistant Cultivars
When you purchase seeds, ask if they are resistant to carrot flies or if they are early-maturing and fast-growing.
The adult flies find the carrots by an acid they give off called chlorogenic acid. The larvae also need this to survive in the roots. There are some low chlorogenic acid varieties. These include:
- Maestro F1
- Ibiza
- Flyfree
- Paranoid
- HealthMaster
- Ingot F1
- Resistafly F1
3. Floating Row Covers
The first thing to remember is if you use a row cover, you must practice crop rotation. This is because the pupae overwinter in the soil, so if you cover the crop from above, they will come up from below, where they are already waiting.
Don’t plant umbellifers in the same area as the year before, or the newly emerged adult fly will be under the cover with full access to your plants for egg-laying.
A floating row cover is a light material that lets in water, sunlight, and air, but not pests. This cover from Agribon would work well for controlling carrot flies.
4. Skip One Year of Sowing Umbillifers
If you have trouble with carrot flies one year, you could simply not plant carrots during the next season. That’s right, skip a year. Do the same with all umbellifers.
The adults are not good flyers and don’t move far. By skipping a year, you are depriving them of any host plant. Likely, the carrot fly won’t find your carrots when you start planting them again for several years.
If you’re going to try this step, it needs to go hand-in-hand with the following one.
5. Keep Weeds Away
Weeds like wild carrots (aka Queen Anne’s lace or Daucus carota), cow parsley (Anthriscus sylvestris), fool’s parsley (Aethusa cynapium), hemlock (Conium maculatum), and other umbellifers should be cleared from all surrounding areas.
These weeds are widespread, and many people don’t even realize that they’re around.
But as long as you have umbellifers in the area, carrot flies will always show up.
6. Interplanting
There is one type of plant that you should intercrop carrots and their relatives with. These are alliums like onions, garlic, and leeks. Plant alliums in rows or clumps between umbellifers.
Onions, garlic, chives, and leeks confuse the larvae. This makes them a good natural line of defense.
7. Remove Crop Residue and Rotate Crop
Ensure you remove any unharvested carrots after the growing season to minimize the carrot fly’s ability to overwinter in the roots.
You should always follow a crop rotation gardening program, but it is particularly important when you have issues with pests like carrot flies who overwinter, waiting for the next season of carrots to be planted.
8. Use Sticky Traps
There are sticky traps available that can be used for carrot flies. They need to be planted in the close vicinity of the carrot crops, and no higher than three feet.
This will serve two purposes. Firstly, it will let you know if you have carrot fly adults. Secondly, the more you catch, the more you prevent them from laying eggs around the crop.
Sticky traps will capture multiple different species, both good and bad, so they are best used to let you know that carrot flies are present and not as a method of control.
9. Use Beneficial Nematodes
You can buy beneficial nematodes that can be watered into the soil that can kill eggs and larvae. These nematodes are not specific to carrot flies but are beneficial in protecting against many soil-borne pests.
This pack from Amazon contains three different species totaling five million nematodes to kill up to 200 species of pests. Follow the manufacturer’s directions to apply to the soil and control larval pests.
10. Don’t Thin Carrots Out
When you thin out the carrot rows, a smell is released when you remove the seedling that attracts the female carrot fly looking for suitable hosts.
Instead, plant sparsely so you don’t have to thin out the seedlings. Carrot seeds are tiny, but I’ve been known to create a line of holes with a dibbler and place one seed in each hole. It takes extra prep work, but it’s worth it when you don’t have to deal with carrot fly damage.
