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Soybeans Today January 1998

Researchers Aim for Redvine Control

By Rich Maples

A team of University of Arkansas Division of Agriculture researchers is looking at tillage and herbicide options for controlling the state’s No. 1 perennial vine problem, redvine.

U of A weed scientist Dr. Dick Oliver, agronomist Dr. Terry Keisling and graduate student Tate Castillo have put in 50-foot by 50-foot plots on Jimmy Fletcher’s farm near Keiser to compare four approaches to tillage and four herbicide treatments. The on-going study is being funded by the Arkansas Soybean Promotion Board.

"We put in tillage treatments in the fall of 1996," says Oliver. "We’re looking at four tillage levels: no-till, conventional tillage, use of a moldboard plow and use of a hyperbolic subsoiler.

"Across each of the tillage plots, we put in four herbicide treatments. One treatment had no herbicide. We just evaluated the tillage. In two treatments, dicamba (Banvel) was applied at a rate of 2 pounds per acre. In one of the treatments, the dicamba was broadcast. The second dicamba treatment involved spot spraying with a backpack sprayer."

The fourth herbicide treatment, two applications of Roundup on the Group IV Roundup-Ready soybeans planted in 1997, were done during the growing season. The Roundup applications were made at the V2 stage of growth and then about three weeks later at the V6 stage.

V2 is when there’s one fully expanded trifoliate leaf with a second leaf just separated, which is usually 10-14 days after emergence. The V6 stage is when there are five fully expanded trifoliate leaves with a sixth leaf just separated.

Oliver noted that the backpack sprayer used to apply dicamba in the fall of 1996 was replaced during the fall of ‘97 with a new Detect sprayer that automatically turns on its nozzles when it senses green mass.

"We didn’t have the new sprayer in ‘96, so we simulated how it works with the backpack sprayer," said Oliver. "We spot sprayed to see if we could cut down on the cost of controlling redvine with dicamba. It’s expensive to broadcast the herbicide."

He said spot treating can be as effective as broadcast spraying because redvine generally grows in clumps and not across the entire field.

With the exception of the Roundup applications, all of the tillage and herbicide treatments were done in the fall. The dicamba treatments were made prior to harvest, but after the plants reached physiological maturity. The leaves and pods had turned yellow.

"Up at Keiser, in Northeast Arkansas, if you harvest your soybeans before you apply the herbicide, you won’t get enough regrowth of the vines to get good control," explained Oliver.

"Our past experience shows that Roundup, like the dicamba, needs to be applied in the fall, when the vine is translocating down. You want to get control of those underground stems."

The first year of the project produced some excellent results. "We knew 15 years ago when we did work with dicamba that it was outstanding for redvine," said Oliver. "In this test, both our spot and broadcast treatments with dicamba gave us 98-100 percent control. Whether this treatment holds off the redvine next year remains to be seen.

"We rated the effectiveness of Roundup throughout the growing season and found that Roundup alone gave about 80 percent control. It knocked out the tips of the terminals and stopped the vine from climbing, but we don’t know if the weed will come back next year."

Oliver said use of the moldboard plow gave about 90 percent control of the redvine. "By plowing the ground, you’re cutting off those underground stems."

The two other tillage treatments--conventional and subsoil--gave only 30 percent control of the redvine. "We just broke off the vines, and they regenerated quickly," he said.

One of the unique features of the redvine control study is the use of aerial photographs and the Global Positioning System, or GPS, to map where the vines were located at the beginning of the project.

"Over the next two or three years, we can use the map to tell us where the vines have moved or if we’ve controlled them," said Oliver.

Information on soybean weed control is available at your county Cooperative Extension Service office.

Soybeans Today January 1998
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