Weed Resistance Spreading Rapidly ─ Two New Species Confirmed in Iowa

Greensboro, NC, USA, December xx, 2009 – According to Mike Owen, Iowa State University Associate Chair and Professor of Agronomy, recent in-field experiments have confirmed the evolution of glyphosate-resistant weed populations in Iowa. Specifically, cases of glyphosate-resistant common waterhemp and giant ragweed, two of the most yield-robbing weeds for Iowa producers, have been confirmed.

“While glyphosate resistance is not confirmed widely across Iowa, anecdotal information suggests that the occurrence of resistance is increasing rapidly,” said Owen.

Warnings about the development of glyphosate-resistant waterhemp in Iowa were publicized as early as 2000 when Owen began advising growers to implement resistance management practices. University experts in Iowa were some of the first to discuss glyphosate-resistant weeds and their potential impact. “Throw in the fact that the frequency of glyphosate resistance is relatively low, the resistant gene(s) trait to progeny has not occurred in grower fields as rapidly as ALS resistance,” said Owen. “But the potential is there unless growers are willing to adopt resistance management practices.”

“Unfortunately, our predictions about glyphosate resistance have come to pass and common waterhemp, as well as giant ragweed, have now been confirmed in Iowa,” said Chuck Foresman, manager of weed resistance strategies for Syngenta Crop Protection. “Glyphosate-resistant weeds currently affect an estimated 7.5 million U.S. row crop acres in corn, soybeans and cotton.” Syngenta expects that number to grow to about one in four acres, by 2013.

Although Owen and Foresman agree it may not be possible to prevent the spread of resistance, they also agree that, with careful management, growers can at least delay the spread of the problem and help preserve the glyphosate technology.

Foresman urges growers across the nation, including those in Iowa who are now experiencing the problem first-hand, to recognize the importance and reality of resistance, develop a plan to combat the problem on their fields and in their community and, most importantly, take action now.

“Resistance can be managed successfully, but it requires adjustments to current weed management strategies,” said Foresman. “Growers must alternate chemistries and avoid over-reliance on glyphosate. The use of residual herbicides such as Prefix® pre-emergence or Flexstar® GT post-emergence in soybeans and Lumax®, Lexar® or Halex® GT in corn is also critical to the management of resistance. Not only do these products include residual components, they also offer multiple modes of action, which allow growers to diversify chemistries in one application.”

Iowa retailer Matt Appel has seen the negative impact of using glyphosate followed by glyphosate, and now recommends that his customers incorporate pre-emergence, residual herbicides into their weed management program to combat glyphosate resistance.

“We like our customers to use a residual herbicide like Prefix on their beans followed by Touchdown Total®,” said Appel. “Prefix helps our customers avoid yield loss due to weed competition. It does a better job controlling waterhemp, helps with application timings and keeps fields clean during adverse weather conditions. The fields with nothing down get very weedy and it hurts yields. Prefix is a better strategy for weed resistance management.”

To build a customized solution specific to their unique challenges, growers can visit the Solutions Builder at www.resistancefighter.com.

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