Palmer Pigweed and Glyphosate-Resistance

Palmer pigweed (Palmer amaranth), the king of all pigweeds, is the fifth glyphosate-resistant weed species to be documented in the United States.  As the dominant pigweed species in the South, it was the first weed to develop resistance to glyphosate in the U.S. and has the potential to inflict catastrophic damage if the problem becomes widespread.  Weed scientists report that it could change the way growers farm.

Dr. Ken Smith, University of Arkansas extension weed specialists, recently discussed the looming problem of Palmer pigweed resistance in cotton. To hear his comments, click here.

The widespread distribution and high density of Palmer pigweed in the South reinforces the need to carefully monitor fields and be aware of escapes. Multiple resistance is also a threat with Palmer pigweed, particularly in areas such as in Georgia where ALS resistance is already documented. In addition, Palmer pigweed has been proven to hybridize with other Amaranthus species.  As the graphic above denotes, there are many areas throughout the United States that are battling severe pigweed infestations.  When you throw hybridization and herbicide-resistant populations into the mix, particularly ALS resistance, this competitive weed can be even more challenging. Click here to see what states have confirmed glyphosate-resistant Palmer pigweed populations Palmer pigweed has documented resistance to several modes of action.

Detailed recommendations for controlling Palmer pigweed in cotton, soybeans, peanuts and corn can be found here.

*Data for Figure 1 provided by Doane® Agricultural Services