Dig a lodged corn stalk. Wash the roots. Brown, ragged, chewed-back roots and a slender white worm with a dark head and a dark plate on the tail are corn rootworm. Hill soil around a goosenecked stalk that is still green. Knock beetles off green silks into soap while pollen is still shedding. Plant next year’s corn on a different hill. A spray will not kill the larva already in the root.
Corn rootworms are leaf beetles. The western adult is yellow with smudged black stripes. The northern adult is plain green or tan. The southern adult is the spotted cucumber beetle. Eggs of the western and northern beetles sit in last year’s corn soil and hatch in early summer. The larva does the real damage. The adult clips silks later.
- Wash the roots. A white worm with a dark tail plate confirms it.
- Plant next year’s corn on a different hill.
- A spray will not kill the larva already in the root.
Plant next year’s corn on a different hill — a spray will not kill the larva in the root
Once the larva is inside the root, a foliar spray does not reach it. Farm soil granules and Bt rootworm seed are not a backyard finish. Keep this year’s stalk standing, knock beetles off green silks, then plant next year’s corn on a different hill so the hatch finds no corn roots.
- Confirm. Dig a lodged or wilted stalk. Wash the soil off the roots in a bucket. Brown scars, ragged tips, or a missing ring of roots, plus a slender white worm with a brown head and a dark plate on the tail, are this pest. A hard yellow jointed larva after sod is a different insect.
- Hill a goosenecked stalk that is still green. Push soil up around the curve so the plant can stand and finish pollination. Do not pull a green stalk to “get them.” The larva is already in the root mass, and the ear can still fill.
- Knock beetles off green silks into soapy water each cool morning until the silks turn brown. Adults clip silks and can leave a poorly filled cob. After the silks brown, pollination is done. A spray then does not fill the ear. Metallic green beetles with white tufts on the silk are Japanese beetles, not this beetle.
- Pull stalks after harvest and disturb that hill. Western and northern eggs sit in the top few inches of last year’s corn soil. Volunteer corn on that same ground still feeds the hatch.
- Plant next year’s corn on a different hill. Newly hatched western and northern larvae do not walk far. Moving sweet corn across the garden leaves those hatchlings without corn roots. Do not put corn on last year’s squash or cucumber patch if spotted beetles were thick on those flowers. Fail if a bottle on this year’s roots is the whole plan.
Will a spray kill corn rootworm larvae in the soil?
No reliable backyard foliar spray reaches the larva already in the root. Farm in-furrow products and Bt rootworm hybrids are not the home-garden finish. Move next year’s corn. Knock adults off green silks.
Does crop rotation stop corn rootworms?
Yes, for western and northern beetles in a home garden, if next year’s corn is not on last year’s corn hill. Larvae do not walk far. Adults still fly in to clip silks. In some Corn Belt counties western beetles also lay eggs in beans. Watch a new hill after beans in those counties.
Dig the lodged stalk: ragged brown roots and a worm that looks two-headed
The larva is white and slender, up to about half an inch, with a brown head and a dark plate on the tail that makes it look two-headed. It tunnels corn roots from about June into July. The stalk yellows, wilts in heat, or lodges after wind. A plant that grows back in a curve is goosenecked. That is pruned roots, not a broken stalk.
Western adults are about a quarter inch, yellow, with smudged stripes that stop before the wing tips, a yellow underside, and black legs. Northern adults are the same size, plain green or tan, with no stripes. Southern adults are yellow-green with twelve black spots. They are the same insect as the spotted cucumber beetle. Adults feed on pollen and green silks. Western beetles may also scrape leaves into pale parchment patches when numbers are high.
| Where you see it | What it is | Try this |
|---|---|---|
| Lodged or goosenecked corn; brown ragged roots; white slender worm with a dark tail plate | Corn rootworm | Hill the green stalk; plant next year’s corn elsewhere |
| Yellow beetle, smudged stripes, yellow belly, black legs, on corn silk | Western corn rootworm adult | Knock into soap while silks are still green |
| Plain green or tan beetle, no stripes, on corn silk | Northern corn rootworm adult | Same job as the western adult |
| Hard, shiny, yellow-brown jointed larva; often after sod | Wireworm leftover | See wireworm — not this worm |
| Fat C-shaped white grub with a brown head | White grub leftover | Not this slender rootworm |
| Striped caterpillar in the ear tip | Corn earworm leftover | See corn earworm — not a soil larva |
What do corn rootworms look like?
The larva is a slender white worm up to about half an inch, with a brown head and a dark plate on the tail. Western adults are yellow with smudged stripes and a yellow belly. Northern adults are plain green or tan. Confirm by washing the roots of a lodged stalk.
Clean stripes on a cucumber are a different beetle
Striped cucumber beetles have three clean black stripes that run to the wing tips, a black underside, and yellowish legs. They chew cucumber, melon, and squash seedlings and can move bacterial wilt. Western corn rootworm has smudged stripes, a yellow belly, and black legs. It is a corn-root job. See striped cucumber beetles. Do not run that wilt test or that seedling cover on a corn hill.
Twelve black spots on a yellow-green beetle are southern corn rootworm, the same insect as the spotted cucumber beetle. On squash, melon, bean, or rose flowers, use that beetle’s method. Do not paste that flower-knock job here as the finish for western and northern larvae in a corn hill.
A hard, shiny, yellow-brown larva with obvious joints, often after sod, is wireworm. A fat C-shaped grub is a white grub, not this slender worm. A striped caterpillar in the ear tip is corn earworm. Metallic green beetles with white tufts clipping silk are Japanese beetles. A hole in the stalk with sawdust, and a solid stalk that snapped, is a borer leftover, not pruned roots. Pointers only.
How do I tell western corn rootworm from striped cucumber beetle?
Western corn rootworm has smudged stripes that stop before the tip, a yellow underside, and black legs. Striped cucumber beetle has three clean stripes to the tip, a black underside, and yellowish legs. See striped cucumber beetles for that insect.
Are southern corn rootworms the same as spotted cucumber beetles?
Yes. That adult is yellow-green with twelve black spots. On corn roots it is called southern corn rootworm. On squash, melon, and flowers, see spotted cucumber beetles. Western and northern larvae in a corn hill are the usual lodging job.
Is this the same as corn earworm?
No. Corn earworm is a moth caterpillar that eats kernels at the ear tip. Corn rootworm is a beetle larva on the roots, and an adult beetle on the silks. See corn earworm for the worm in the cob.
Related reading
- Spotted cucumber beetle — twelve spots; the southern corn rootworm adult on cucurbits and flowers.
- Striped cucumber beetle — three clean stripes on cucumber and melon, not smudged stripes on corn.
- Wireworm — hard, jointed, yellow-brown larvae after sod.
- Corn earworm — a caterpillar in the ear tip, not a worm on the roots.
- Japanese beetle — metallic green silk clipper with white tufts.
FAQ
Will Bt corn or beneficial nematodes finish rootworms in a backyard?
Bt rootworm traits are a farm seed package, and resistance is already common in parts of the Corn Belt. Beneficial nematodes are not a reliable home-garden rate for this larva. Move the hill. Do not treat a bottle or a nematode pack as the finish.
Can I eat corn if beetles clipped the silks?
Yes. Clip away a poorly filled tip. Firm kernels are food. A cob that is mushy, moldy, or riddled is discard. Silk clipping after the silks have already browned does not take the ear.
Do corn rootworms bite people?
No. Adults chew pollen, silks, and some leaves. They are not a biting pest. You do not spray a hill because a beetle walked across your hand.
Do I need to spray Japanese beetles on the same silks?
Metallic green beetles with white tufts are Japanese beetles. They also clip green silks. Knock them into soap while silks are green, then see Japanese beetles for that insect. Do not run that trap-and-lawn job as the corn-root finish.
Related pests
Related diseases
Updated: Reviewed by Bosquelle Editors