Sometimes the easiest way to regain control over carrot rust flies, Psila rosae, also called carrot root maggots, is simply to stop growing carrots (and other plants that can host carrot flies, like parsnip, celery, celeriac and dill) for a year.
Once the carrot fly has found your garden, it will come back again and again. The flies overwinter as pupae and adults emerge in late spring and start to lay eggs in the soil near carrots and their relatives, then the larvae burrow into the soil and start to chew on and tunnel into carrot roots, leaving your harvest criss-crossed with blackened, rotting tunnels. But if you don’t grow any carrots or carrot relatives that year, the poor flies have to wander off elsewhere to look for food. Being weak fliers, they don’t go far and likely won’t find a host plant. Most will simply die in transit.
The following spring, there will be no carrot flies in the sector and therefore no damage.
It tends to take carrot flies at least 5 to 6 years to find your garden again, often a decade … at which time you can again thwart them by not sowing anything they can eat for a year.
Insect control by starvation? Why not!
Won’t Work in Community Gardens
Note that this method will probably not work in community gardens, as there will almost certainly be other gardeners growing carrots just a few lots from yours … unless you can convince the whole garden community to not grow carrots for a year. But it works wonderfully in individual home gardens.