MOULTRIE — If anyone ever wanted to make a farm-themed horror movie, a hardy variety of pigweed would be a prime candidate for the villain’s role.

The mutant weed is immune to many herbicides in farmers’ arsenals, produces up to half a million seeds that can be spread by wind or by hitching a ride on farm equipment — thus passing the herbicide resistance to pigweed in other fields — and if not controlled can grow to as thick as a baseball bat and taller than an NBA center.

And it crowds out cotton plants, devastating a whole field if it can’t be stopped.

In the third year Colquitt County farmers have had to deal with it, many are forced to resort to pulling the weed by hand, a practice that is both time-consuming and expensive.

At this time there is no way to eliminate the Palmer amaranth that has become resistant to glyphosate, the generic name of Roundup, one of the most popular herbicides used in cotton production. But growers are trying to minimize its spread by hand-pulling and thorough cleaning of equipment.

The glyphosate-resistant Palmer amaranth was first confirmed in 2005 in Macon County, and has since been confirmed in 19 more, including Colquitt the very next year.

For years glyphosate was the equivalent to farmers and lawn enthusiasts of what penicillin was in combating harmful bacteria — something that worked with the added benefit of minimal environmental impact.

But like the overprescription of antibiotics has caused resistance to develop among bacteria, overuse of the herbicide led to a decline in its effectiveness, Colquitt County extension agent Scott Brown said.

Glyphosate-based herbicides work by inhibiting a specific enzyme that plants need in order to grow, according to the Web site howstuffworks.com. Without the enzyme plants cannot produce other proteins necessary for growth. Since most plants use the enzyme it works on nearly anything, making it a favorite of farmers, foresters, gardeners and biologists controlling invasive exotic plants.

A farmer killing 99.999 percent of pigweed each year for seven or eight years eventually has among the survivors a weed that is resistant to the chemical, Brown said. That produces a process of natural selection in which the glphosate-resistant strain predominates.

“The problem is now there’s so much out there (that) at some point you’re going to have it,” Brown said.

He estimated that 70 percent of cotton farmers likely have some presence of the Roundup-resistant plant.

“Next year it will be very difficult to find a field in Colquitt County that does not have glyphosate-resistant pigweed,” he said. “I think we’re getting phenomenal performance if you only have a dozen here and a dozen there in a field. They’ve done a lot of things to reduce the pigweeds down. That’s important because it keeps the seed level down.”

Farmer Brian Robinson, who had his first confirmed glphosate-resistant pigweed in cotton this year, said he is hand-pulling weeds in fields where pigweed survived two applications of Roundup. Some of the weeds have reached a height of five feet.

“It’s just real scattered,” he said. “You’ll go and you’ll spray a field and you’ll have little spots. It might be one spot, it might be two spots, it might be 10 spots.”

The cost of hand-pulling weeds could run as high as $100 per acre in fields with a high concentration of the pigweed, although he personally has not had any that were that severe. Combining herbicide cocktails has also been successful, although the additional applications also increases costs.

That presents additional economic pressure in a year in which cotton farmers already are squeezed.

“There’s not any room — the way the cotton prices are, and the chemical costs and fuel costs — it’s going to be a struggle just to get your money back,” Robinson said.

In the future, Robinson, who uses conservation-tillage practices that use minimal tilling, said he may have to examine whether more harrowing, and the additional costs that will mean, is more economical than battling the resistant pigweed later in the farm season.

“I don’t know how we’re going to handle them,” he said. “I know we’re going to have to make some changes. I don’t know what we’re going to do. We’re going to have to do something to control this pigweed.”

In the meantime Robinson is making cleaning equipment a top priority to avoid transporting the resistant pigweed.

“A cotton picker is a major cause of picking them up,” he said. “Seeds get on the head of a cotton picker. You might leave some in every field. That’s probably my biggest fear is contaminating equipment and moving them myself.”

In terms of new technology to combat the Palmer amaranth, farmers will have to wait until 2013 or 2014, said University of Georgia extension agronomist Stanley Culpepper.

That technology will come in the form of seed with genetic resistance to a chemical that can be applied to cotton.

In the interim farmers will have to use other methods of control that can increase weed control cost by three times, Culpepper said.

“The only economical program at this point is to prevent it from getting a foothold on your farm,” he said. “If you as a grower can keep it out for two or three years, that is the best thing you can do.”

That means battling the pigweed early, as a quarter inch plant with the resistance can survive a solution of Roundup applied at 10 times the normal amount, he said.

“It’s devastating our cotton industry,” Culpepper said. “In simplistic terms it means a complete change in managing weeds in Roundup-ready cotton. The ease of the program, the economics of the program are all going to go away.

“When you develop resistance to it where you don’t even slow down the growth of pigweed, you’ve lost the most economical way to control this pest.”