• Glyphosate-resistant Palmer pigweed threatens to propel weed control through a time-warp.
• Solutions are emerging. One is zero tolerance.
• Zero tolerance attacks the Achilles’ heel of Palmer pigweed, its seed.
• Zero tolerance combines hand hoeing and supplemental herbicide application.
• Solutions won’t be cheap.
Robert Goodson, a county agent for the Arkansas Extension Service, says fighting them is a constant battle. “There are spots in the field where we chopped them, and we’d go back a second time, and if the roots from the chopped plant are on the ground, they’ll grow. I hate ’em.”
Hindsley spent close to $75 an acre on the zero tolerance field, compared to the $20 an acre he would spend on three shots of Roundup, prior to glyphosate-resistant pigweed. Unfortunately, those days are gone.
“Over the last 200 years, the easiest farming years have been the last 10 years to 12 years with Roundup control,” Hindsley said. “Now we’ve got this resistance, and it’s hard on us. It’s more expensive. It takes more labor, and we may have to rethink what we’re doing, including downsizing.”
Andrew Wargo, AACD president and farm manager for Baxter Land Co., in southeast Arkansas, says he has already seen a decline in rent values in pigweed infested fields. “And ag lenders are concerned that a producer farming an infested area is going to have more out-of-pocket costs and a smaller profit margin. In the last 12 to 14 months, we’ve seen some real awareness of that.”
In Georgia, where resistant pigweed first appeared in 2005, there have been amendments to conservation plans that allow some tillage used in conjunction with cover crops to control glyphosate-resistant pigweed. Weed scientist Jason Norsworthy is studying such a combination in research plots at the Lon Mann Cotton Research Station in Marianna, Ark. The research is paid in part by Monsanto.
In 2008, half a million glyphosate-resistant Palmer amaranth seed were placed in 22-foot square sections within cotton plots, each consisting of 8 rows, 300 feet in length. “We ran a disk over the field two times, then put in our tillage with and without a moldboard plow and with and without a cover crop of ryegrass,” Norsworthy said.
In 2008, the moldboard plow alone provided a 62 percent to 65 percent reduction in Palmer amaranth emergence, the same as the performance of the rye cover crop alone. Together, the two practices resulted in an 86 percent reduction in Palmer pigweed emergence. The moldboard plow was used only in the first year of the experiment.
“I’m not a big fan of a moldboard plow, due to erosion issues,” Norsworthy said, “but the data indicates if you use it on a very small acreage and put a cover crop back on top, it can be quite effective in suppressing pigweed emergence. The next step is to begin to overlay effective herbicides on top of that.”
The same practices in soybeans were much more effective, according to Norsworthy, who will tabulate findings after three growing seasons.