Glyphosate Resistance Continues to Spread in the South

Palmer pigweed is a tough weed to control, and it becomes even more difficult to manage once glyphosate resistance enters the picture.  In the South, Georgia [North Carolina isn’t confirmed on HRAC, Syngenta’s “authority,” so we can’t mention it] has already confirmed glyphosate-resistant Palmer pigweed, and it is suspected in Tennessee, Arkansas and North Carolina.  According to this research article from Louisiana State University Ag Center, Louisiana now has suspected glyphosate resistance to Palmer pigweed as well.[It’s not confirmed it’s Palmer, it’s a pigweed yet to be determined]. The problem has not been confined to a single field or county, demonstrating that this is not from a single population.

As the dominant pigweed species in the South, Palmer pigweed was the first pigweed to develop resistance to glyphosate in the U.S. that has the potential to inflict catastrophic damage if the problem becomes widespread due to it’s competitive nature. Weed scientists report that it could change the way growers farm.

The fact that this pigweed species has not positively been identified reminds us that pigweed species hybridize easily. Glyphosate resistance in cotton will cause drastic changes in management. There is no easy answer. Pictures in the mentioned article show plants surviving glyphosate applications of more than 100 oz. of glyphosate. Not only does that add to herbicide application costs, but adds  

If such a damaging weed is spreading, should growers who do not practice resistance management strategies be held accountable?  Is it time to mandate Best Management Practices with glyphosate? Several areas around the U.S. have reported additional concerns with weed escapes and glyphosate control. How much of a problem do you expect glyphosate resistant weed problems to be this year compared to previous years? Why?

For more information about this troublesome weed, and for Syngenta’s recommendations on how to manage it, click here. For LSU’s resistance management recommendations for glyphosate-tolerant cotton, visit http://www.lsuagcenter.com/en/crops_livestock/crops/Cotton/Weed+Control/Herbicide+Resistance+Management+in+Roundup+Ready+Cotton.htm.