Something's eating my carrots, potatoes, radishes (2024)

George Weigel

Floating row cover protecting this patch of a vegetable garden.

I've had problems the past year or two with something, insects I suppose, boring holes into my carrots, potatoes and radishes. Any idea what it might be and what I can do?

A: Bugs like vegetables as much as we do. With leaf-eating insects on root crops, the good news is that you sometimes can salvage a decent crop without doing anything. More of a problem are bugs that bore into the actual roots and tubers.

Particular bugs typically attack particular crops. That's good news and bad news. The good news is that you often only need worry about one or two key bugs attacking a crop. The bad news is that adds up to a lot of different bugs to keep track of throughout a diverse veggie garden.

I think there's a good chance three different bugs are boring holes in your carrots, potatoes and radishes.
On carrots, rust flies lay eggs at the base of the leaves, and the eggs hatch into larvae that tunnel into the carrot roots and cause significant damage. Draping the plants with floating row cover stops the egg-laying and therefore the damage. Row covers are light-weight blankets thin enough to let water and sunlight through without smothering plants. Some people build tubular frames to drape them over, but I just drape them over plants and hold down the edges with bricks. Row covers are available in some garden centers and through garden catalogs such as Gardens Alive (www.gardensalive.com), W. Atlee Burpee (www.burpee.com) and Planet Natural (www.planetnatural.com).

On potatoes: wireworms, beetle grubs, tuber worms, corn borers and weevils are all bugs that can tunnel into the tubers. Wireworms and grubs tend to be worst in new gardens that were dug from what had been lawn. These are common pests of turfgrass but also appreciate a good potato dinner.

Floating row covers work great at stopping almost all tunneling bugs because they keep out the flying adults that attempt to lay the eggs that turn into larvae that then bore into roots and tubers. Stop the egg-laying, flying adults and you stop the larvae. The down side is that if you've got row covers over everything, your garden will look more like a sheet factory after a tornado blew through. Row covers also have to be removed when fruiting crops flower in order to allow pollinating insects to do their job.

Mulches are another option at discouraging egg-laying. A thick layer of straw is the traditional choice, but some gardeners swear by wood ashes sprinkled around root crops as an antidote to borer egg-laying. And smelly and/or repellent sprays also may help, such as neem oil or VeggiePharm (mint and garlic). These can help repel carrot rust flies, too.

The worst potato pest is the Colorado potato beetle, which feeds voraciously on potato leaves to the point of stunting yield. These are big enough to easily see when they're feeding. You can hand-pick and squish them (the choice of veteran organic gardeners) or spray them. Neem oil, VeggiePharm, insecticidal soap and the promising new bacterium-based Spinosad (the ingredient in Capt. Jack's Deadbug Brew) are organic spray options. Rotenone and Sevin are veggie-approved insecticides that'll make the beetles drop.

On radishes, flea beetles often attack the leaves, while cabbage maggots are a common root tunneler. Flea beetles are pinhead-sized black bugs that make buckshot holes in the leaves. Maggots are little white wormy-looking critters that bore into and all throughout the roots.