Herbicide resistant weeds have changed the way Georgia cotton farms manage their crop and the potential exists that similar situations may develop across the Cotton Belt if farmers fail to heed lessons Georgia growers have learned.

Stanley Culpepper, Georgia Extension weed specialist, described the Georgia experience with amaranth species during the recent Texas Plant Protection Association annual meeting in College Station.

“Amaranth species resistance is changing the way we grow cotton across the belt,” Culpepper said. “We’ve seen significant changes the last five years because of this ‘super weed.’”

He said resistance came on rapidly in Georgia. “In 2004, we had resistance on one farm,” he said. “In 2005, we identified resistance in 2 counties. In 2009, we have 13 counties with resistant weeds.”

He said the problem occurs across the Southeast and Mid-south. “Growers created resistance with selection process by using only glyphosate herbicide,” he said.

Changing practices

Georgia may have been the first to have the problem and the effect on the way farmers manage their crops has been significant. “We lost about half our conservation tillage acreage from 2004 through 2008,” Culpepper said. “We lost another 50 percent through 2010. John Deere has sold a lot of breaking plows. We’ve seen as much as a 20 percent increase in cultivation.”

He said cotton farmers also are turning back to incorporated herbicides. “We have to do it.”

Some are adding Liberty Link varieties to their operations and controlling weeds with Ignite herbicide.

Farmers are also hand weeding. “They pull weeds and carry them out of the field,” Culpepper said. A 2009 survey of 800,000 acres indicated 54 percent of the cotton was hand weeded. “Grower cost ranges from more than $3 an acre to $100 per acre. Average is $26 per acre. Total cost to hand weed the Georgia crop was $11.4 million.”

In 2010, Culpepper said, resistant weeds caused one farmer to lose a farm. He could no longer rent land.

It shouldn’t have gotten this bad, Culpepper said. “We tried in 2005 to get farmers to use a preventive program for about $35 an acre. No one would do it. Today, we’re spending $65 per acre on herbicides and hand weeding and cultivating. We’ve invested $130 million in Palmer Amaranth control, and we’re not making much progress.”

He said resistance is real. In trials, they applied glyphosate at rates significantly higher than label rates and still did not get control. The weed outcompetes cotton plants. “It does not shut down,” Culpepper said. “It will grow when cotton is wilting in the heat. They grow very fast and get extremely tall.”