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Managing insects can add bushels to soybean yields

Fine-tuning insect management can increase per-acre soybean yields by two or three bushels. Early planting is one management tool that proved its value in 2012. Because of last year’s good spring weather, many Arkansas growers planted soybeans in late March and early April.

“About 20 percent to 30 percent of our late-planted beans experienced heavy insect pressure,” says Gus Lorenz, Extension IPM specialist with the University of Arkansas in Lonoke.

“Bollworms were extremely heavy in late-planted and double-cropped beans; we also had loopers and stink bugs. So plant part of your acreage as early as possible within the optimum timeframe.”

The optimum planting window varies yearly, according to environmental conditions and geographic area. “South of I-40, we can plant in late March and mid-April,” Lorenz says. “North of I-40, the planting window falls in mid-April.”

Additionally, seed treatments protect beans from the below-ground pest complex that includes grape colaspis, rootworms, wireworms and grubs. Seed treatments also suppress above-ground pests, including three-cornered alfalfa hoppers, bean leaf beetles and thrips. 

Georgia soybeans need scouting for kudzu bugs this year. “It will be an economic problem statewide,” says Phillip Roberts, Extension entomologist with the University of Georgia at Tifton. “We encourage growers and scouts to sample with sweep nets, and treat at a one immature per sweep threshold.” 

Kudzu bugs are easy to control, but challenging to manage, Roberts says. “If we start spraying for kudzu bugs early, we might alter our whole insect control program because early sprays could disrupt beneficial insects and flare up later insect pests. However, don’t treat too much for this pest — it takes many kudzu bugs to cause economic damage.”

Stink bugs historically are the most yield-limiting pest in Georgia soybeans. The state’s second-most-important insect group is defoliating caterpillars, mainly soybean loopers and velvetbean caterpillars. Growers also need to watch for lesser cornstalk borers. 

Most of Mississippi’s early soybean crop in 2012 experienced the lightest insect pressure in years, says Angus Cat-chot, Extension entomologist at Mississippi State University, Starkville.

“Most growers didn’t apply insecticides, even with their R3 fungicide application. However, we had to control some insects in late-planted or double-cropped beans. We sprayed late-planted beans for bollworms around July 10.

“Growers should plant early, when possible, to minimize exposure to insect pests, including soybean loopers, bollworms and stink bugs.”

Bayer CropScience’s Belt is one of the newest chemistries labeled in soybeans, Catchot says. “It’s very efficacious on corn earworms and offers long residual looper control. Pending EPA approval, we also might have Prevathon by DuPont and Besiege by Syngenta. Both provide outstanding caterpillar control and extremely good residual control.” 

The kudzu bug was an issue in South Carolina soybeans in 2011 and 2012 and is expected to be one in 2013, says Jeremy Greene, Clemson University entomologist, Blackville.

“However, stink bugs have been a predictable perennial problem for our soybean growers for some time. They represent our most damaging insect pests by infesting a large percentage of our fields regularly, particularly late season.

“Additionally, the corn earworm or podworm is an issue. We can’t stand many of these pod feeders in the field — not like we can tolerate some defoliation from caterpillar pests that include green cloverworms, soybean loopers, and velvetbean caterpillars, which can be troublesome in southern South Carolina.

“These defoliators can also cause problems every year. To maximize profit, growers need to have a crop consultant checking their acres and recommending timely IPM strategies,” Catchot says.

Tennessee’s major soybean insect pests are stink bugs, corn earworms and three-cornered alfalfa hoppers, says Scott Stewart, Extension entomologist at the University of Tennessee, Jackson. 

“Stink bugs are our No. 1 pest, primarily green stink bugs. Few corn earworm problems occurred in 2012. However, we had heavy infestations of the three-cornered alfalfa hopper; their feeding on seedling beans caused girdling damage, resulting in lodging later.

“We can also have defoliating caterpillar pests, including soybean looper and green cloverworm. We have new good insecticides such as Belt, which controls corn earworms and loopers. Other insecticides might be labeled for 2013, including Prevathon and Besiege.”

Tennessee continues monitoring the kudzu bug. “It has now been confirmed in several counties in both east and middle Tennessee,” Stewart says. “A few fields were sprayed in 2012, and we expect it to be more common throughout Tennessee in 2013.”

Stink bugs were present in Alabama soybeans last year but damage was not as severe as usual due to lower populations, says Tim Reed, Extension entomologist at Auburn University, Belle Mina.

“Predominant species in north Alabama were the green and brown stink bug. In south Alabama, southern green stink bugs and brown stink bugs were the most common stink bugs,” 

Three-cornered alfalfa hoppers continue to be a concern. More soybeans are being planted with an insecticide seed treatment to deal with this problem, especially in double-cropped beans.   

“Some data indicate high populations of late-season three-cornered alfalfa hoppers, say two to three per sweep on R5 beans, can cause economic yield losses,” Reed says. “In this case, growers can check for other insects in the field, and determine the potential damage from the complex in making their application decision.   

“Soybean loopers were a significant statewide pest in 2012 with numerous north Alabama fields requiring treatment for the first time since 1988.

“Green cloverworms and velvetbean caterpillars are easy to control, while loopers are more expensive to manage. However, without scouting, it is possible to lose all foliage to those species.”

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