Glyphosate-resistant Palmer pigweed has been confirmed at two locations in west Tennessee, making it the second finding of resistance in the weed species in the nation, say University of Tennessee weed scientists.
Scientists at the University of Georgia and Monsanto earlier this summer confirmed glyphosate-resistant Palmer pigweed in Georgia.
University of Tennessee Extension weed specialist Larry Steckel says Palmer pigweed at locations in Lauderdale and Crockett counties in West Tennessee survived an application of 22 full ounces of Roundup WeatherMax. Plants at one location survived an application of 44 ounces.
University of Tennessee Extension weed scientist Tom Mueller says, "In some ways the Palmer pigweed appears to be similar to glyphosate-tolerant horseweed/mareâ€™s tail. All the treated Palmer pigweed plants look the same for two or three days after the application. They all wilt and turn yellow."
About four days after spraying, the tolerant plants stop wilting and begin new growth in lateral buds.
As far as control is concerned, proper applications of Clarity, 2,4-D, Gramoxone Max or Ignite "will allow farmers to produce pretty clean crops," Steckel says. "However, we expect resistant Palmer pigweed will pose more problems for producers than horseweed."
The discovery of resistant Palmer pigweed reinforces the importance of managing weed resistance to herbicides. "It is essential to use more than one herbicidal mode of action in your fields," Mueller says.
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