Low insect spray environment brings new challenges in cotton

Many cotton producers, particularly those in east Alabama, have had light insect pressure now for almost a decade. Even so, they shouldn’t make the mistake of letting down their guards, says Ron Smith, Auburn University Extension entomologist.

“Most growers in light insect pressure environments are handling insect control as economically as possible,” said Smith at the recent East Alabama Cotton Production Meeting. “But you should make sure that you have a system in place that’ll alert you to any traditional insect problems, such as worms or plant bugs. Sooner or later, we’re going to see an increase in some of those primary pests — if not in all fields, then in some fields.”

Sporadic insect pests also may cause economic damage in some years, he adds, and someone needs to be watching for these problems. “You’re putting yourself at great risk to try and grow cotton in this part of the world without someone monitoring for insects,” he says.

Alabama cotton producers continue to find certain insect pests in their fields each year, although they may be only isolated cases, says Smith. Some of these insects might be considered emerging pests in the current low-spray environment, he says.

“For example, in the last few years, grasshoppers have been a problem in a lot of areas of the state, but it appears to have started in central Alabama,” he says.

Several things, he adds, have caused this sporadic pest, including eliminating the boll weevil and planting Bt cotton and eliminating worm sprays. “Another thing, and it may be more important than the other reasons, is the movement to reduced-tillage production,” says Smith.

One thing growers need to know about grasshoppers is that they’re only an economic pest when cotton is in the seedling stage, he says. “Once cotton gets five or six true leaves, grasshoppers tend to feed on the leaves. But they never eat enough leaves to hurt anything. It’s only when they’re cutting off the seedling cotton that grasshoppers become a problem,” says Smith.

Growers can pretty much ignore grasshoppers if they don’t see them until after cotton is at the six to eight or more true-leaf stage.

“The only other thing you need to know about grasshoppers is if you think you need to spray in that seedling stage, the immature stage of the pest that jumps around is easy to control. Anything you put out that’s labeled for cotton will work.

“However, if it’s June, and a lot of grasshoppers have moved into the adult stage and can fly, they may be difficult to kill. They’ll require a very high rate of a pyrethroid or a product like Orthene.”

Grasshoppers usually are in the fields prior to planting in reduced-tillage situations, says Smith, and some growers have even considered putting some control material in with their burndown treatment.

Some cotton producers are seeing more Southern armyworms in their fields than in the past, he says. “They’re almost 99-percent foliage feeders, and unless you have a lot of them, you can ignore them. They may eat all of the leaves off one plant, where the egg mass is located, but they don’t go to the fruit very much

“They’re a little like beet armyworms when they start, except they don’t go to the fruit as badly. On the Gulf Coast, when growers get enough of them, about 1 percent of the population will feed in the fruit. You can possibly get bloom, square or boll damage from the Southern armyworm.”

The leaf-footed plant bug also is becoming more common in today’s low-spray insect environment, says Smith. They commonly are seen in home gardens, as they prefer feeding on tomato plants in the fall, he says.

“The damage from this pest is similar to that from stink bugs. If we’re looking internally in bolls for stink bug problems, that’s when we’ll be picking up on the leaf-footed plant bug. They also are mid to late-season boll feeders.”

For two consecutive years, says Smith, the vegetable weevil took out a cotton field in central Alabama. “We haven’t seen them before or since, but it’s also a pest, at times, in the Mid-South.”

The three-cornered alfalfa hopper, he says, is a sporadic cotton pest that typically moves into fields from roadsides that have been mowed.

“They’ll move in when the grass is dying down and cotton is in the early planting stages. Symptoms include a plant that takes on a reddening appearance with an enlarged place on the stems where three-cornered alfalfa hoppers have fed. They prevent the flow of nutrients from moving up and down the plant, and we might see more of these pests as we expand our peanut acreage.”

Before growers began planting Bollgard cotton, it wasn’t uncommon, says Smith, to see European corn borers in cotton fields that were adjacent to corn. “They bore into the stem, or they can go into the boll. If they bore into the stem, they’ll leave a trail of sawdust-like material down the edge of the plant.”

The cotton leafworm, he says, was a fairly common occurrence in the Southeast in the 1920s and 1930s. “As far as spraying insecticides, we’ve just about moved back to that day because we’re really not using any foliar insecticides. These insects migrate up from the tropics, and they’re strictly foliage feeders. You’ll see the pupae stage of this insect hanging from the leaf of a plant.”

Early season fall armyworms tend to get on pigweed, says Smith, and when growers burn down the pigweed, they move to cotton. This has been a common occurrence for several years now, he says.

“False chinch bugs move into cotton in tremendous numbers during a dry season. They can damage cotton in the seedling stage by sucking the juice from it. But the false chinch bug is not a pest in cotton.”

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