PORTAGEVILLE, Mo. — Mare's tail, a familiar nemesis for Missouri farmers, has reappeared with a new resistance to glyphosate-based herbicides, a University of Missouri weed scientist said.
Mare's tail, also known as horseweed in the Delta region, "isn't a new problem, but until recently, glyphosate controlled it," said Andy Kendig, weed science specialist at MU Delta Research Center in Portageville. "Now, we see fields where everything is burnt down except horseweed. It's really erupted over the past two years."
Glyphosate is the active ingredient in Roundup and other herbicides, upon which some farmers rely almost exclusively. "Some of the mare's tail problem is due to glyphosate-only burndown treatments," Kendig said. "The good news is that we have a couple of very good treatment options. The bad news is that it doesn't always get done."
MU researchers recommend a March application of an herbicide such as 2,4-D [2,4-Dichlorophenoxyacetic acid CAS# 94-75-7] or Clarity [Dicamba, diglycolamine salt CAS# 104040-79-1], he said. "These two herbicides are essential to control mare's tail — or primrose or several other troublesome weeds. Even if there are a few late-germinating horseweeds that escape, this application is still needed."
Without the pre-plant burndown application, he said, "you have to go with mediocre cleanup options. There are only a few choices," including "old-fashioned tillage."
Andy Kendig (573) 379-5431
Forrest Rose Information Specialist (573) 882-6843 RoseF@missouri.edu
source: http://agebb.missouri.edu/news/queries/showcur.idc?story_num=2895&iln=696 8aug2004
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