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Resistant weeds’ new foe

University of Arkansas Division of Agriculture scientists and farmers are optimistic about a new tool in the fight against glyphosate-resistant weeds: LibertyLink soybeans.

“We currently have five different weeds that are glyphosate-resistant including horseweed, both common and giant ragweed, pigweed and most recently johnsongrass,” said Bob Scott, division weed scientist.

Bayer Crop Science released LibertyLink soybeans in 2009. The soybeans are tolerant to the herbicide Ignite.

“Ignite and Roundup are different modes of action so this provides us with a new tool for managing glyphosate-resistant weeds,” Scott said.

The University of Arkansas is the only university to have LibertyLink soybeans for three years. “With funding from the Arkansas Soybean Promotion Board, we tested LibertyLink soybeans for the past three years to see how this technology would fit into Arkansas’ soybean production system, evaluate its strengths and weaknesses and then be ready for recommendations in our MP-44,” said Scott. “I think it’s a real success story of how we cooperated with a company to have our recommendations ready for the producers when the technology hit the market.”

Division scientists believe LibertyLink soybeans are the biggest development to come along in soybeans since Roundup Ready soybeans hit the market a decade ago.

“This technology represents the first truly unique new mode of action we’ve had for soybeans in a while and it represents our best tool to fight glyphosate-resistant weeds.”

One LibertyLink soybean study was conducted in Crittenden County, Ark.

“We saw some very impressive results and we think this is definitely something to get excited about,” said Mike Hamilton, Crittenden County Extension agent.

Dick Oliver, division weed scientist, said additional studies were conducted at the Pine Tree Branch Research Station in Colt, Ark., and Northeast Research and Extension Center in Keiser, Ark.

“So far, the beans are looking good, so I think we’ll have some good yields,” Oliver said. “I’ve been very impressed with the results. Ignite has really done a nice job on weed control.”

Why are division scientists and county agents excited about LibertyLink soybeans?

“This technology represents the only true replacement technology available to growers to replace Roundup Ready soybeans,” said Scott.

Oliver said LibertyLink soybeans should be a good option for those growers who’ve gone to a no-tillage system; continue to plant soybeans without crop rotation, or who continue to spray the same herbicide.

“When growers can add another tool to controlling resistance, it helps break the chain of resistance,” said Oliver. “The key to controlling resistant weeds is stopping the reproduction. Once a weed reproduces … you’ve got a problem.”

While there is plenty to be excited about, LibertyLink soybeans do have some challenges. From the research plots researchers learned some residual herbicide is needed to make the LibertyLink system work better. Second, to kill pigweed Ignite must be applied earlier than glyphosate has historically been applied. Two applications of Ignite are needed for complete control of pigweed and other weeds.

“There are a few things that are different but, in general, the LibertyLink system will allow a grower to continue farming the way he’s been doing it without changing up his practices too much,” Scott said.

Jeremy Ross, division soybean agronomist, said the LibertyLink soybeans are currently being tested in the university’s variety trials program.

“We first tested for weed control in 2007 and 2008,” Ross said. “Now we’re conducting the variety trials and looking at how the varieties perform.” While the division has one year of data on the varieties, scientists like to have two years of data before making recommendations.

When Roundup Ready soybeans were introduced about a decade ago, approximately 90 percent of the state’s soybean acreage became Roundup Ready. Over the years, this use put tremendous selection pressure on the technology and resulted in the development of resistant weeds.

“To put it simply, Mother Nature doesn’t like a monoculture,” said Ken Smith, division weed scientist. “She doesn’t want everything to look the same and conform.”

Crittenden County is all too familiar with resistant weeds. This county has confirmed the presence of all five glyphosate-resistant weeds. The biggest problem, though, is Palmer amaranth, or pigweed.

“We’ve developed a game plan for controlling horseweed; we’re getting ragweed under control, and johnsongrass has only been found in one location. Pigweed is the one we’re really battling,” Hamilton said.

His sentiments about pigweed ring true with just about every grower in the state, whether they’re growing cotton or soybeans.

“Palmer pigweed was found at some level in 750,000 acres this year,” said Smith. The problem is so prolific it drew the attention of ABC World News, which sent a reporter and videographers to Marvell, Ark., in the summer to cover the story.

Pace Hindsley, a Marvell farmer, said the problem is forcing growers to go back to older ways of farming, including hand-hoeing to get the weeds out of the fields.

“We’re not just worried about the problem this year, but also next year and the year after that and each year until we can get a solution to the problem,” said Hindsley.

In addition to the frustrations caused by battling pigweed, cost is also a major consideration.

“You get to a point where it’s just not financially feasible to do anything else and you have to live with the results you’ve got,” said Jim Hubbard, who also farms in Marvell. “You pull your hair out because you’ve done everything you know to do and you just can’t beat this weed.”

The division scientists all stress that LibertyLink soybeans should be used as a tool to combat resistant weeds and farmers shouldn’t turn to relying solely on this technology.

“Any time new chemistry is introduced, there’s always a fear of overuse, overdependence,” said Hamilton. “We need to alternate the chemistry used to fight weeds. LibertyLink soybeans give us one more tool we can use in conjunction with other methods to fight resistant weeds.”

TAGS: Soybean
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