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Careful monitoring of insects in soybean fields and assessing how much threat they pose to crop yield could result in fewer insecticide applications and greater cost savings, says Angus Catchot, associate Extension professor of entomology and plant pathology at Mississippi State University.
Other soybean pest problems
Another soybean pest, green cloverworms, is present in most soybean fields every year, Catchot notes. “They show up early, and they’re around the entire season. A lot of people still confuse them with loopers. Green cloverworms have three sets of prolegs, loopers have two. Also, when you disturb them, cloverworms will flip and jump around like crazy, and loopers won’t.
“The confusion occurs when you catch small green cloverworms in a sweep net — they will ‘loop’ like a soybean looper and people confuse this instead of counting prolegs.”
Outbreaks of velvetbean caterpillars occur every 10 years or so, particularly in the hill areas, he says. “We had them in a few spots last year, and they can cause extensive defoliation, but they’re easy to control. You just need to be able to identify them and treat as necessary.”
Soybean loopers can cause massive defoliation when numbers are high, Catchot says. “But, if you know you’ve got soybean loopers, please don’t treat them with pyrethroids or Orthene, even at the highest rates. It’s not worth the risk of flaring them. Instead, use materials that work, such as Steward, Belt, or Intrepid.
“The worst application you’ll ever make is one that doesn’t work.
From R-3 until R-6 is a very critical time for defoliation. If you get 100 percent defoliation at R-3, it can be catastrophic. At R-5, the yield loss is not as steep, but will still result in major yield loss. At R-6, you can still get yield loss, but your chief concern at this point is to keep pest numbers from building to massive levels. Essentially, at early R6 you are guarding against the 80 percent to 100 percent defoliation events.”
Mississippi soybean growers sprayed 650,000 acres last year for bollworms, some as many as four times, Catchot says. “We had higher numbers than we’ve seen in many years, and there were no peaks and valleys — they were sustained for 4-6 weeks, with no really distinct peaks.
“We’re pushing our soybean plantings earlier every year. But now that we’re planting more grain and trying to spread out harvest, we’re planting more Group Vs and more wheat beans, which exposes us more to stink bugs, loopers, and bollworms.