February 5, 2016
Monsanto announced on Feb. 3 that Roundup Ready 2 Xtend soybeans have gained import approval in China. This is long-awaited news for Arkansas producers, because seed for planting this technology has been available for at least a year now.
Researchers at the University of Arkansas System Division of Agriculture have been heavily involved over the last five years in developing weed control programs and evaluating the usefulness of the Xtend soybean and cotton systems. This comes at a crucial time for our soybean and cotton producers in Arkansas with pigweed populations becoming resistant to another class of herbicides commonly used.
In 2015, Palmer amaranth, the most troubling weed in soybean and cotton crops, was found to be resistant to PPO herbicides such as Valor and Flexstar. These populations were discovered in 15 counties, most in northeast Arkansas. At this writing, we have screened more than 100 samples in the greenhouse and have found pigweed resistant to PPO herbicides in the following counties in Arkansas: Clay, Conway, Craighead, Crittenden, Greene, Independence, Jackson, Lawrence, Lee, Lonoke, Mississippi, Poinsett, Phillips, White and Woodruff.
Even though Chinese approval of this new technology is a critical step forward that allows another tool for control of problem weeds, unfortunately there are currently no dicamba-containing herbicides labeled for pre-emerge (for use at planting) or postemergence (over-the-top) use in Bollgard II XtendFlex cotton or Roundup Ready 2 Xtend soybeans.
Based on reports and communications with industry leaders, we do not know for sure that we will get a label for a dicamba herbicide by planting time this year or even for early postemergence applications in either of these crops.
This is disturbing because never in the past has other herbicide-tolerant technology been released without the herbicide being labeled for use in the crop. Weed scientists at the University of Arkansas Cooperative Extension Service recommend that growers facing PPO resistance in their fields rotate to other crops such as corn or rice, or plant cotton or soybean cultivars that are LibertyLink or tolerant to Liberty herbicide, such as Widestrike cotton.
Bollgard II XtendFlex cotton is tolerant to over-the-top applications of glyphosate (Roundup), glufosinate (Liberty) and dicamba herbicides. Because the XtendFlex cotton cultivars are also tolerant to Liberty herbicide, effective weed control programs can be developed for glyphosate and PPO-resistant pigweed. However, Roundup Ready 2 Xtend soybeans are only tolerant to glyphosate and dicamba herbicides; they are not tolerant to Liberty.
Due to the fact that there is no current dicamba herbicide labeled in Xtend soybean and there is no herbicide option for control of glyphosate and PPO-resistant pigweed once they emerge in the field, we do not recommend planting the Roundup Ready 2 Xtend soybean in fields or counties that have an infestation of PPO-resistant pigweed.
Another point that should be considered is this: The University of Arkansas System Division of Agriculture has only a minimal amount of data regarding soybean yield of these new varieties. We don’t have enough data to know how they will yield right out of the gate.
Growers that farm in these counties should be prepared to deal with PPO-resistant pigweed, even if they did not have a confirmation of resistance in 2015. Pigweed seed can be spread several ways including equipment, birds and floods.
It is great news that we have finally moved forward with getting this technology approved and in the hands of our producers. However, it is also frustrating, because by not having a dicamba labeled for use in this technology we are most likely headed for a train wreck due to the lack of herbicide options in Xtend soybean for glyphosate and PPO-resistant pigweed.
Tom Barber is an Extension Weed Scientist with the University of Arkansas System Division of Agriculture. [email protected]
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