Prior to Roundup Ready technology, herbicide systems used to kill pigweed in cotton were not foolproof, so when a few escapes started popping up in cotton fields during the past few years, farmers didn’t pay much attention.
In 2006, the escapes became parts of whole fields and the same farmers found that double and triple rates of glyphosate had no effect on these pigweed. Herbicide resistant pigweed now scares them to death, and the heavy dependence on glyphosate and ALS herbicides has created a situation that offers only a few alternatives, and none of them are cheap.
There is no doubt that glyphosate resistance is more widespread than previously reported. Alan York, a weed scientist at North Carolina State University began a wide-scale program in 2005 and found pockets of resistant Palmer pigweed around the state.
Similar, but less formal studies in Georgia and South Carolina indicate the widespread existence of resistant pigweed in those states.
In South Carolina, Clemson Extension Weed Specialist Chris Main says farmers are in a situation where they have to have a solution, but it has to be an economic solution to allow them to stay in the cotton business.
Growers simply can’t pay $80-90 per acre for weed control, when they have been living in a world since 1997 in which Roundup Ready varieties reduced cost to $20-25 per acre.
The worse case scenario imaginable for farmers with large acreages of peanuts and cotton is to have cross resistance to both glyphosate and ALS inhibitors. Though not quite ready to roll out the scientific evidence, weed scientists in the Southeast privately contend just such a cross resistance is more likely than not.
In 2006, there is some evidence that Italian ryegrass, lambsquarters and cocklebur may have developed resistance to glyphosate.