TIFTON, Ga. — The cotton industry is concerned about a herbicide-resistant weed that spreads easily, can grow an inch a day and could force farmers to return to growing methods that were harsher on the environment.

Palmer amaranth, a type of pig weed, grows 6 to 10 feet tall. If someone were trying to design a particularly nasty weed, Palmer amaranth could be the model, said Alan York, weed scientist at North Carolina State University in Raleigh.

"It's an extremely competitive weed," he said. "It's extremely prolific. It's an efficient ... bad weed."

Amaranth that resists the most common herbicide used in cotton, glyphostate, has been confirmed in 10 of North Carolina's 100 counties, four of Georgia's 159 counties and is suspected in Tennessee, South Carolina and Arkansas.

"It is potentially the worse threat since the boll weevil," said York.

York was referring to the voracious beetle that devastated Southern cotton crops in the early 1900s and forced farmers to switch to alternatives such as peanuts.