Cotton Belt weed experts know that herbicide resistant Palmer amaranth isn’t exactly new. The first documented cases of resistant pigweed date as far back as 1989.
The current pigweed dilemma, of course, arises from its resistance to glyphosate – a product that cotton producers across the Belt had come to rely heavily upon. That’s why weed experts at the Beltwide Cotton Conferences in January focused on the new weapons that are available to combat this familiar problem.
“There’s no doubt that Palmer pigweed is the driver weed,” said Larry Steckel, Extension weed expert with the University of Tennessee. “It doesn’t matter what you do managing these other weeds if you don’t take care of Palmer.”
Steckel spoke about managing the new technologies that are available to cotton producers, whether they operate in a glyphosate or glufosinate based herbicide system. He noted the similarities between the two systems, saying it is a necessity to overlap residual herbicides in both.
In Tennessee, Steckel says, roughly 80% of the cotton acres planted in 2012 received an application of Liberty herbicide over the top. While that represents a startling shift in herbicide management systems, Steckel advocates that if Roundup herbicide is still effective on their farms, growers would be wise to continue to incorporate it into their programs.
“If you can keep Roundup in play, you’re going to be better off,” Steckel noted.
Because so many of his state’s acres utilized Liberty in 2012, Steckel and other Tennessee cotton professionals were able to make notes of how to use it most effectively. For starters, Steckel said, the time of the Liberty application is important. Steckel and his fellow researchers ran tests where they were spraying five to six inch pigweeds at various times of day, from early morning to sunset.
“The take home point was that we were seeing very poor performance about the time the sun was coming up. But any time later in the day, we were seeing much better performance,” Steckel said.
Steckel also noted that Liberty will be a very effective herbicide when used in combination with dicamba, once dicamba-tolerant traits are available from the cotton seed companies. In addition to providing a wider window to control fast-growing Palmer amaranth, dicamba will also provide protection against further herbicide resistance.
Still, despite the promising prospects of a Liberty plus dicamba system, Steckel says growers will not have it as easy or cheap as they did when Roundup first became available. This past season, he estimates that growers in his state spent nearly $100 an acre on their herbicide programs.
Growers in Georgia have unfortunately become familiar with spending large amounts in their weed management programs, according to University of Georgia Extension weed expert Stanley Culpepper. Still, Culpepper said cotton producers in his state had a successful year in battling the herbicide resistant epidemic.
“2012 was our first good year in managing Palmer amaranth since we discovered it,” Culpepper said. “We reduced hand weeding by about half in 2012 compared to 2011.” That stat alone saved growers in the Peach State roughly $7.5 million in crop protection, Culpepper says.
Culpepper credits that success to better herbicide programs that have been simplified for grower use. Georgia growers have learned which products are best for use on dryland acres that may need a longer window to become activated.
“In our state we know that we can put Valor, Reflex and Staple on the ground, and if it rains 15 days from now, they’ll be there, they’ll be activated and provide excellent control for Palmer amaranth,” Culpepper says. “It’s the little things like this that we learn about individual herbicides that allow us to place them in our program and make us better overall.”