Carrot root fly is a serious problem for anyone who grows carrots. The fly’s maggots can kill off seedlings and also burrow into the roots of mature plants, leaving brown, unsightly tunnels behind. Carrot root fly also affects parsnips and even celery.
There are a few different ways to stop root fly, but using a fleece is probably the best option, especially since they’re most active during April and May, as well as July and August. That being said, the fleece can end up crushing the foliage if it’s not supported properly. If you need to remove the fleece for any reason, do so during the evening when root fly are less active.
One way to keep carrot root fly off your carrots is to grow them in a tall raised bed or in barrels. Another is to put up a vertical barrier, as the fly generally doesn’t fly high off the ground.
Inter planting / Companion Planting
The root fly is attracted to the smell of carrots and its foliage. Inter planting with onions or leeks can help to disguise the smell. I have had success in growing my carrots in a square foot bed next to onions.
The best way to prevent carrot root fly is to use a combination of all three methods. If carrot root fly is a problem in your area, you can also try resistant varieties, such as Flyaway.