Carrot Weevil
Listronotus oregonensis
A small native weevil that is one of the most damaging pests of carrots, parsley, and celery across the eastern United States and Great Lakes region. The adults nibble foliage and do little harm, but their grubs tunnel down into the crown and root, where they ruin the edible part and open the door to rot.
🔎 How to spot it
Adults are dark brown, hard-shelled weevils about a quarter inch long with the snout typical of weevils. They overwinter hidden in the top couple inches of soil and in weeds, grass, and debris along field edges, then walk into the crop in spring. The larvae are small, legless, white grubs with brown heads that feed inside the crown and root. Look for adults on the soil at the base of plants and for dark zigzag tunnels packed with frass when you pull and split a damaged root.
🥀 Damage it causes
The grubs cause the real loss. They tunnel through the crown and down into the root, leaving winding feeding channels that make carrots, parsnips, parsley, and celery unmarketable and often cause the survivors to crack and rot. Heavy infestations can ruin half the crop. Adult foliage feeding is minor by comparison.
🛡️ Prevent it
Rotate carrots and related crops well away from last year ground, since the overwintered adults walk rather than fly and a long move strips them of an easy start. Clean up weeds, grass, and crop debris along bed edges where adults shelter through winter. Delaying sowing can help, because females lay eggs mainly into plants past the four-true-leaf stage, so a late stand escapes some of the early egg laying.
🧯 If it is already here
There is no rescue spray once grubs are inside the root, so timing is everything. Monitor in spring with carrot-disc baits or boards to catch the first adults, and act before heavy egg laying. Floating row cover sealed at the edges from emergence onward keeps the walking adults off the crop. Tiny native Anaphes wasps parasitize the eggs and can destroy a large share of them in undisturbed plantings.
💡 Good to know
Because the weevils walk in from the edges and overwinter in place, the single most useful home-garden step is to not grow carrots, parsley, or celery in the same spot two years running. Pull and destroy infested roots rather than composting them, so any grubs inside do not complete development nearby.
🌱 Plants it attacks
18 plants in the library can be attacked by this pest
For educational and informational purposes only. Pest control advice is general guidance drawn from university cooperative extension sources; always identify a pest positively and read and follow the label on any product before use, especially around food crops, children, and pets.