Carrot fly and carrot root fly problems
The carrot fly is an tiny, evil flying insect which can easily decimate the carrot crop you have so lovingly created and tended. It has a very sharp sense of smell which will direct it to its chosen root where it lays an egg which, when it turns into a grub, burrows into your carrot and usually makes it inedible.
In brief, this little pest starts out as an egg, then a grub (pls see pic) which eats those circular holes in your carrots before maturing into the adult fly whereupon it takes off to mate and the whole cycle starts once more.
If your crop is unprotected against carrot fly it could easily be infested more than once in any given growing season.
Carrot fly prevention.
The carrot flies fly only a few inches above ground so any unprotected crop at ground level is fair game for them. One very effective method of avoiding infestation is to plant your crop in raised beds or tubs which are higher than the pest normally flies.
Another method is to purchase some insect proof netting which not only frustrates the carrot fly's efforts to lay eggs on your crop but also allows air and rain to come through.
AN even less expensive of keeping the carrot fly at bay is to plant with alternate rows of onions, starting with a row of onions nearest the front edge of your plot. The onion smell masks the lighter smell of the carrots so the fly leaves well alone.
A number of gardening experts will tell you that the carrot fly invasion has finished by mid-June, but that depends on where you live in our country where the growing season varies so much due to the different temperatures in the North, Midlands and South. I keep my nets on until it is time to pull the crop.