Managing insect pests in corn important to making top yields

It seems producers are planting earlier every year. And with good reason, says Glenn Studebaker. “We need to plant early,” said the Arkansas Extension entomologist at the recent Multi-County Feed Grain Meeting in Brinkley, Ark. “Doing so helps to avoid many insect problems that can occur later in the season.”

But Studebaker warns there can be a razor-thin line between “early” and “too early.”

Insects are cold-blooded organisms that don't survive well over the winter. During the winter months, they can hibernate but suffer significant mortality in most populations.

Generally, in the spring, insect populations are the lowest in Arkansas crops. As the summer arrives, they begin to reproduce. Many of the insects have short life cycles and they build up to their highest numbers in late summer.

“So if producers can get their crops planted early enough that they're mature and done before insect populations get really high, many problems can be avoided.”

Corn seed maggots

But there is an exception to every rule, says Studebaker. In the case of early-season corn worries, seed corn maggots are that exception. “Seed corn maggots are among the most common pests in corn … and can get you into trouble if you plant too early. This pest has higher populations early in the spring and it likes wet, cool weather.

“When we plant into a wet, cool seedbed and the seed sits there for a while, it takes up some moisture and doesn't sprout quickly. The longer it sits there, the greater the chances one of the little maggots will find it.”

The maggots aren't looking for corn in particular. They feed on organic matter and are general feeders.

The pest is actually a small fly — a bit smaller than a house fly. Studebaker said he's still seeing many of the flies during warmer days this winter.

“They lay their eggs in recently plowed ground. They don't like to lay eggs in undisturbed ground … so they rarely occur in no-till situations. The larvae hatch out into small maggots and they feed on seed as it grows.”

Seed treatments do control them.

“The in-furrow insecticides we recommend on corn all do a pretty good job controlling seed corn maggots. The best thing to do is plant into a good, warm seedbed so the seed sprouts quickly. Once it sprouts and the seedling is up, the plant is pretty safe from seed corn maggots.”


Another pest seen on Arkansas corn roots — and sometimes seed — is the wireworm.

There are several species of the pest. The common ones are brown to black in color, about 1.5 inches long. The larvae are the crop-damaging stage of the pest.

The larvae will move up and down in the soil while overwintering. Depending on the species, they can live as larvae for one to five years.

“So if you had a problem with wireworms last year, there's a good chance there are still wireworms this year.”

They also tend to be more problematic in lighter, sandier soils.

“Many growers want to plant corn this year and some probably plan to plant some fields that were in pasture or were fallow. Situations with lots of grass mean the chances of having wireworms or grubs are much higher.

“If I had a heavy wireworm population, I'd probably go with Counter. Seed treatments — Cruiser, Poncho, and Gaucho — also help suppress the populations of this pest.”

Fire ants

Fire ants are more of a problem in no-till fields. They prefer not having the soil disturbed and they're able to build mounds more easily in no-till scenarios. Many times the ants are more of a problem around field borders.

“After you plants corn or grain sorghum, fire ants can come into a field and pick the seed apart and carry it off. There are so many fire ants they'll often take out large sections of a row.”

This is an insect with both good and bad aspects. “Fire ants will feed on other insects, so they can be beneficial. They'll carry off seed corn maggots and pest eggs.”

In-furrow insecticides will help suppress or control fire ants.

Southern corn rootworm

The Southern corn rootworm is a common insect in the South. The adult phase of this pest is known as the spotted cucumber beetle.

“They lay eggs in the field in the spring after corn has been planted. It doesn't matter if you've planted corn in a certain field previously or not. They lay eggs in the springs and I've seen them attack roots, as well.”

The larvae, oblong grubs with brown heads, grow to about .75 inch long. They will feed on roots and can cause lodging. Under heavy feeding, plants will fall over.

The reduced root mass will also affect yields, warned Studebaker. Even though corn plants are still growing, “when you pull ears off at harvest they tend to be smaller because the root system was compromised earlier.

“There's no big change on Extension recommendations. The main thing to know about these soil insects is there's nothing that can be done after planting.”

Once the seed is in the ground, “if you haven't made a decision on whether you'll manage these pests, it's too late. You must decide what you'll do about all the insects prior to planting. We can't spray the soil or corn after planting. These pests stay in the soil feeding on the roots.”

Studebaker, stationed in northeast Arkansas, has seen increasing problems with several pests in recent years.

“I've seen more white grubs, rootworm and wireworms lately than what we've had in the past.”

To deal with wireworms, many growers are going with seed treatments.

“The cost isn't too bad. If you get a 4-bushel bump in yield, the seed treatment is often paid for.”

White grubs

“I'm seeing more and more white grubs. There are two species: a true white grub, with a two-year life cycle; and the annual white grub with a one-year life cycle.”

The adults are the big, brown beetles “that come to your windows at night because they're attracted to light. The larvae are big, ‘C-shaped’ grubs that feed on roots. They like grasses, but we've picked them up in soybeans and other crops.”

The true white grubs are the most damaging. In-furrow insecticides do help control them. They come up from the soil when it gets very wet.

“They have long legs at the front, but they don't use them to crawl. They actually crawl on their backs like a worm and can move quickly.”

Chinch bugs

Chinch bugs are tiny insects — adults are about a quarter-inch long. Immature chinch bugs have a white band across their middles and have a reddish tint when very small.

This pest, with a piercing/sucking mouth part, feeds on grasses.

“They like the roots right below the soil on the stem. Even though they aren't a soil insect, per se, they're hard to find and see.”

Typical damage from chinch bugs includes a twisting of the leaves, yellow streaking of leaves, and leaves or even entire seedlings dying. Several adult chinch bugs can kill a small seedling.

“Sometimes you'll notice plants dying in your fields for no obvious reason. If you dig around in the soil, you'll often find chinch bugs feeding.

“You can kill chinch bugs with insecticides. However, getting the insecticide to the bugs is a big challenge. Many products do well on them, but there has to be a heavy volume of water included. Use enough water to get a dose running down the stem a bit to reach where the chinch bugs are.

“Also, Gaucho, Cruiser and Poncho seed treatments help suppress chinch bugs early on seedling corn.”

Stink bugs

Studebaker saw damage from stink bugs on seedling corn in 2006. “Much of the damage was due to brown stink bugs, but the greens and southern greens were in the fields as well.”

This pest has a piercing, sucking mouth part and feeds on seedling corn stems. Primarily that's because “there's not much out there to feed on early. About half the time, corn plants will grow out of stink bug damage. There will just be cosmetic damage — a few oblong holes in the leaves.”

But if they feed on the growing point, they can cause tillering or the death of plants.

“Last year, I saw fields with 10 percent tillering, probably from stink bugs.”

Corn borers

Corn borers can be a big problem in Arkansas corn — particularly in the central and eastern parts of the state.

“The European corn borer is probably the less common one we see. The Southwestern corn borer is more common.

“They both lay their eggs in flat masses that overlap like roof shingles. The European lays 30 to 50 eggs at a time under a leaf and they hatch in about five days.”

The problem in controlling this insect is they're borers. They move into the stem several days after hatching. Once inside the stem “you can't kill them with an insecticide because they won't come back out until they're ready to emerge as adults.”

The larvae of the European corn borer are flesh-colored. Treatment is called for when 50 percent of the plants are infested.

The southwestern corn borer larvae are more of a white color with black spots. They lay their eggs in masses of two to five. The southwestern corn borer is more damaging because it moves down to the lower part of the stem and girdles it.

“Since they bore up and down the stem, they will hurt yield and can cause lodging. The larvae overwinter in stalks.”

The best control for borers is Bt corn varieties. However, because of all the cotton grown in Arkansas, “you can't plant more than 50 percent of your corn to a Bt variety.”

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