• 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.
From 1998 to 2008, weed control on Mid-South cotton farms was perhaps the easiest in the history of U.S. cotton production, thanks to Roundup Ready technology. The next few years, however, could be the hardest.
Glyphosate-resistant Palmer pigweed threatens to propel weed control through a time-warp — from a total post-emergence program to an era when hand choppers, residual herbicides, hooded sprayers and tillage were the tools of the weed control trade.
It’s the latter tool, tillage, which has attracted not only the attention of farmers, but conservation officials from coast to coast. Palmer pigweed not only threatens profits for growers, but tillage can threaten the long-established benefits of conservation, and perhaps place farmers dangerously close to compromising conservation plans.
But solutions are emerging. A recent tour organized by the Arkansas Association of Conservation Districts demonstrated some of the best management practices under consideration to address glyphosate-resistant Palmer pigweed in the Mid-South. The tour was part of a meeting of the National Association of Conservation Districts’ Herbicide Resistance Task Force.
The task force plans to outline recommendations on how to tame weed resistance in areas where it has occurred and prevent resistance where it has yet to happen.
One of the practices demonstrated on the tour was zero tolerance, a research project implemented by Arkansas weed scientist Ken Smith on two Mid-South cotton fields this season.
Zero tolerance attacks the Achilles’ heel of Palmer pigweed, its seed. According to studies conducted by University of Arkansas weed scientist Jason Norsworthy, the weed’s biggest weakness is the short life of its seed in the soil. In fact, 80 percent of Palmer pigweed seed die within one year in the soil. After 4.5 years, virtually none of the seed are viable.
Zero tolerance combines hand hoeing and supplemental herbicide application to ensure that pigweed doesn’t reach maturity and produce seed. Weed scientists believe if they can systematically reduce the seed bank, or the population of viable seed in the soil, they can slowly start to clean up heavily infested fields.
While the practice may make a field manageable again, there’s no way zero tolerance can completely eradicate the plant, or its seed.
“It’s a numbers game,” Smith said. “These seeds produce such high numbers of seed, 200,000 plus seeds per plant. It doesn’t take very many escapes to build up a soil seed bank. That’s what’s happened to us.”