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Corn+Soybean Digest

Check For Chewers

Careful scouting thwarts late-season insects

If you didn't pay attention in '98, insects very likely ripped you off big time. That's tough when profit margins are already paper thin.

Last year, late-season insect pressure across the South was more average. Even so, many growers suffered yield losses they could ill afford.

Since nobody can accurately predict what this season will bring, pay attention, say entomologists. It was a mild winter - good for insects.

"If you didn't pay attention to late-season insect activity in '98, you likely suffered some pretty hefty yield losses - ranging anywhere from 5% to 75%," notes Scott Stewart, Mississippi State University (MSU) entomologist. "You can do everything else right and then screw up badly by not scouting stinkbugs, for example, deep in the campaign."

Jim Hamer, former Mississippi State extension entomologist and now a crop consultant, seconds that observation. "Soybean loopers in '98, where they were not managed, caused significant yield losses. In irrigated fields, where yields weren't affected by dry weather, loopers took up to 10 bu/acre."

"I think most growers are aware of stinkbug damage potential, but how good a job they do of scouting varies a lot," says Jack Baldwin, extension entomologist at Louisiana State University. "And growers who don't do a good job are going to pay the price - in yield, quality, delayed maturity and the green bean effect."

Entomologists agree that some farmers do a super job of insect control in soybeans, some a good job. But many don't.

The key to effective insect control management, say these specialists, boils down to one word - scouting. The problem is the quality of scouting too often isn't good enough to prevent economic damage from profit-stealing insects, say the scientists.

"I think most farmers understand the importance of scouting out insects," says Jim Palmer, recently retired Clemson University extension soybean specialist. "The problem is doing it effectively on a regular basis. I'm afraid there's an awful lot of 'windshield' scouting from the pickup truck. For defoliators that's a way to at least save the crop in some cases, but for pod feeders, it's like a roulette game, and definitely not a good idea."

Not scouting for stinkbugs using a sampling device is a "big mistake," says Hamer.

"If a grower goes into a field in the late season and doesn't detect visual signs of damage, and he doesn't have a sampling device such as a sweep net, then he runs the risk of having damage from stinkbugs that will go undetected until harvest," he says. "When you see black, shriveled seed coming out the back end of the combine, you'll probably say to yourself, 'big mistake. The stinkbugs got me, and I just didn't see them.'"

Insect control in soybeans has always taken a backseat to insect control in cotton because it's a relatively low-value crop, claims MSU's Stewart. "But you can't ignore it and expect to be consistently profitable."

One big reason insects tend to get away with a lot more profit than they should, agree entomologists, is that they are inconsistent in where, when and in what numbers they attack from year to year.

"Insects are not a problem on every farm or every field every year. And 60-70% of the time, you can get away with not paying a lot of attention to insects. But that other 30-40% of the time, you could suffer significant damage in a field or several fields," Stewart explains.

A perfect example was '98, Hamer says. Insect pressure was so intense in some soybean fields that levels exceeded the economic threshold levels by 10 times or more.

Under certain conditions, insects invade fields wherever soybeans are grown. In the southern tier of states from Texas to Georgia and Florida, plus the Carolinas, however, insects can be a real and frequent economic threat. Warmer weather in recent years has brought much greater insect pressure in states like Arkansas, too, especially in 1998.

Many insects are migratory and come in on southern winds, so they may be a big problem in one year and almost no problem the next year.

Insects can invade soybeans from emergence through the late season. But it's the late-season insects, like stinkbugs, loopers, corn earworms and velvetbean caterpillars, that can eat up all your profit from a soybean field. And, in the case of stinkbugs, for example, they can do it quickly and without you knowing it - unless you scout thoroughly with a sampling device, warns Hamer.

"Probably our single biggest insect pest is stinkbugs," agrees Randy Hudson, University of Georgia extension entomologist. "We lose more yield to stinkbugs than anything else, with the southern green stinkbug as the biggest threat here. But we've got a host of foliage feeders. We have some insect infestations in the southern part of the state every year, depending on weather patterns."

Unlike with some disease problems, growers have the tools, including good insecticides, to adequately control profit-stealing insects in soybeans, say these scientists.

"It really boils down to effective scouting and then applying the right insecticides when needed," says Hudson.

Scads of free information on how to scout effectively and economic damage thresholds is available from your state extension service. It will tell you when it pays to treat and when it's prudent to save your money.

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