The cotton industry is concerned about the discovery of a herbicide-resistant weed that spreads easily, can grow an inch a day even during droughts and could force farmers to return to older growing methods that were harsher on the environment. "It is potentially the worse threat since the boll weevil," said Alan York, weed scientist at North Carolina State University in Raleigh, referring to the voracious beetle that devastated Southern cotton crops in the early 1900s and forced farmers to switch to alternatives such as peanuts. The boll weevil was eradicated in some states in the late 1970s and early 1980s, paving the way for the return of cotton as one of the nation's major crops, worth $4.7 billion. It is grown in 16 states from coast to coast.