Corn rootworm is the latest pest bugging cornfields across the Midwest. Both its larva and adult form can severely damage corn, reducing yield and exposing it to other stressors.

Two main species of corn rootworm can be found in the region — northern and western. Purdue University says the western variety is seen as yellow to yellowish-green in color, with a black stripe along the sides of the wing covers. The northern species is tan to pale green, changing to a deeper shade of green as it matures.

Purdue says it’s not necessary to distinguish between the two species because both inflict the same damage. The larvae feed on roots, which reduces nutrient and water uptake by the plant. The feeding sites later become pathways for pathogen infections.

Both species of rootworm have only one generation per year. Eggs are laid in the soil from summer to autumn, and hatch from May to June. The larvae then seek corn roots to feed on while passing through three stages before pupating. Adult beetles emerge in late June to early July, where they feed on pollen, green silks or leaves.

Be alert to signs

No matter the species, here are signs corn might be suffering from one of these rootworm types:

Sampling methods

There are two methods to find rootworms in corn:

Larvae sampling. Sampling for larvae is only needed when an insecticide or hybrid failure is suspected, or a field has a high adult population. Purdue offers these steps:

Adult beetle sampling. Scouting should begin right after corn silking starts. Purdue recommends:

Manage against it

Purdue says a major management strategy for corn rootworm is crop rotations. Rootworms cannot complete their larval development on crops besides corn. If eggs are laid into a cornfield in one season that rotates into a soybean field the next, the larvae are left without a suitable plant and will starve. However, with some variants in the Midwest, crop rotation alone is not fully effective.

For adult beetles, recommended pesticides include chlorpyrifos, alpha-cypermethrin, beta-cyflurthrin, bifenthrin, carbaryl or deltamethrin. For larvae, pesticides include chlorpyrifos, cypermethrin, bifenthrin or chlorantraniliprole.

Your local agronomist, Extension agent or plant protection dealer can offer recommendations for specific farms, fields and varieties. No matter what method you choose, stay alert to this pest to keep corn rootworms out of your fields.