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Do Legwork to Stop the Spread Herbicide-Resistant Weeds

April 19, 2013
palmer amaranth

By Tracy Turner, Courtesy of Ag Answers

Ohio growers, agribusinesses and Ohio State University weed scientists will need to work over the next decade to prevent a weed known to many cotton and soybean farmers in the South as "pigweed on steroids" from further expansion in Ohio, an Ohio State University Extension expert says.

Palmer amaranth, which is a glyphosate-resistant weed that has wreaked havoc for Southern U.S. growers, has been spotted in a large field near Portsmouth in extreme southern Ohio and potentially in a site just south of Columbus, said Mark Loux, an OSU Extension weed specialist.

The concern is that this weed, which has substantially reduced yields and profitability for cotton and soybean growers in Southern states, could become a significant weed problem in Ohio if it continues to spread in the state.

If it takes hold, Palmer amaranth could become even harder to control than the glyphosate-resistant weeds already in Ohio, Loux said. The weed has caused entire cotton and soybean fields to be mowed down in some states.

Waterhemp, another glyphosate-resistant weed, also has resulted in costly herbicide programs and control problems in parts of the Midwest.

"Waterhemp, which is present primarily in a few western counties in Ohio, has proven itself capable of developing resistance to almost any herbicide site of action used against it," Loux said. "Both of these weeds have more potential to impact the profitability of our corn and soybean production than our other resistance problems.

"I don't think we can be too alarmist about these weeds; they could make our current problems seem relatively minor. I'm hopeful that we are still in a prevention mode."

Loux said steps to try to prevent further spread of Palmer amaranth and waterhemp include:

* Identifying new infestations as soon as they occur, preferably when the plant is small enough that herbicides are still effective. Growers with fields that have been spread with manure from animal operations using cottonseed products as a feed need to be particularly aware, as this manure may contain Palmer amaranth seed.

* Using the right herbicide at the right time. Both waterhemp and Palmer amaranth have extended period of emergence and require a combination of preemergence and postemergence herbicides.

* Preventing further seed production by any means possible is also essential to minimize the rate of population increase. "That can include tillage, mowing and pulling the plant out by hand," Loux said.

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