Root vegetables are great because they’re a lot like buried treasure: Plant a few seeds, and dig up delicious treats a few months later.

Unfortunately, just because they’re tucked underneath the soil doesn’t mean they’re immune from pests.

Carrot rust flies love the sweet smell of carrots and will tunnel throughout the entire root, effectively ruining the crop. They’re tiny, less than a quarter of an inch, black flies that lay eggs in the ground near the carrots, parsley, or parsnips. The grubs burrow into the roots.

Sometimes you can tell you have a problem if the carrot foliage turns a brownish orange, then yellow, but you’ll find out for sure when you dig them. It takes the fun out of harvesting when you pull up carrots marred by holes and tunnels.

Preventing Carrot Rust Flies

The best course of action is to prevent the carrot rust fly if you’ve had problems in the past. Breaking out the floating row cover is a good option to prevent them. Just be sure to keep it pinned securely at the base so they dont find their way underneath to your carrots.

Because carrot rust flies don’t fly very high you can grow carrots in elevated containers. This is one instance where patio growing has its benefits. This is also good news because they dont travel terribly far, unlike aphids that will fly hundreds of miles on wind currents.

Other natural options include spreading down a good layer of compost, grass clippings or wood ashes. (The ashes also help give carrots additional potash to develop root growth.) This layer interferes with the adult flys ability to effectively lay eggs in the soil, and at least may reduce the numbers.

Planting onions in between rows of carrots seems to help shield them from the flies. It’s also worth growing garlic, pennyroyal, and marigolds to try to mask the carrots enticing aroma.

And since the grubs overwinter while burrowed into carrots, its yet another reason to rotate crops. They wait until warm weather returns to pupate and fly off to create the next generation.

Pesticide Options

As far as pesticides go, Diazinon was the go-to chemical to take care of these nasty little flies, but its off of the market. (The EPA found it affected the brain and nervous system in humans, and wasnt much good for the wildlife, either. Its been off the shelves for at least five years, but was one of the most popular pesticides homeowners had in their arsenal against pests.) Neem and pyrethrum show some promise, but theres debate on how effective they are in heavy infestations.

Carrot rust flies are tough ones to battle when you have them, but if you stay on top of the situation and make conditions as lousy as possible youll prevent them from using your carrot patch as a nursery and daycare for the little grubs.