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LibertyLink new weapon against resistant weed problem

LibertyLink soybeans have received final approval from the European Commission for importation into the European Union for food and animal feed use. The American Soybean Association said approval will allow the commercial launch of LibertyLink soybeans in the United States for the 2009 planting season.

Bob Scott, Extension weed scientist with the University of Arkansas Division of Agriculture, said LibertyLink herbicide will probably replace Monsanto’s Roundup Ready soybean system on many farms with weeds that have developed resistance to Roundup Ready herbicide and glyphosate, its active ingredient in generic products.

“When the Roundup Ready system was introduced several years ago, it caught on and changed the way farmers farmed,” Scott said. “It could be applied to fully-grown weeds and Roundup Ready soybeans and be effective on the weeds without harming the soybeans, which was a convenience for farmers.”

However, in recent years, several weeds have become resistant to glyphosate.

LibertyLink crops have been modified to resist Ignite herbicide, which is effective on glyphosate-resistant weeds.

“It’s a new soybean weed control system with a different mode of action,” Scott said. He said farmers will appreciate Ignite’s effectiveness against glyphosate-resistant Palmer amaranth, or pigweed, a serious weed pest on many farms.

Now that many weeds have become resistant to glyphosate, it has forced farmers to use combinations of conventional herbicides. This worked with varying degrees of success. It also meant, in some cases, a possible return to tillage as a control method.

“LibertyLink is a post-emerge broad spectrum herbicide that allows you to keep on farming just like you did with glyphosate, but with certain drawbacks,” Scott said.

He listed these drawbacks:

• Glyphosate can kill large weeds, which means farmers can wait and spray at their convenience. With Ignite, applications need to be made earlier and to smaller weeds.

• With certain weeds such as pigweed and barnyard grass, Ignite will work better when farmers first apply a residual herbicide to a recently planted crop. With glyphosate, farmers didn’t need a residual herbicide.

• Another concern is how LibertyLink varieties will perform. Farmers and universities aren’t sure that LibertyLink will be available in varieties Arkansas and Mid-South farmers want. There was a similar concern when Roundup Ready soybeans were initially introduced.

• LibertyLink won’t be as convenient and easy to use as glyphosate because of the need for proper timing of applications and the need for a residual herbicide. Bayer and the University of Arkansas will recommend 22 ounces per acre of product applied 10 to 12 days after planting with a follow up application of 22 ounces per acre about two weeks later.

• The last concern is for problems caused by herbicide drift. Neither LibertyLink nor Roundup Ready soybeans can tolerate the other’s herbicide, so if farmers have fields of each crop close together, “they’d better be careful,” Scott said.

“The university has been evaluating LibertyLink varieties in weed control tests for two years, but it will take another year or two to get a handle on how all the varieties perform,” Scott said. “They’re unproven in the field.”

“Hopefully, we’ll have many of these LibertyLink varieties in the U of A soybean variety test trials in 2009 to evaluate yield, disease and nematode ratings, chloride sensitivity and other agronomic characteristics,” said Jeremy Ross, Arkansas Extension soybean specialist.

Bayer has only enough seed to plant 250,000 to 300,000 acres of Mid-South varieties next year, Scott noted.

He said the system presents challenges, “but the overriding thing is we’ve got fields where glyphosate just isn’t working anymore.”

Scott cautions farmers: “If we simply fall in and use only Ignite for weed control, we will be in the same herbicide resistance trap again in a few years. This makes the use of residual herbicides in the LibertyLink program a good fit for resistance management.”


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