The problem has gotten much bigger and more difficult in recent years.

Waterhemp populations have evolved to withstand atrazine, ALS-inhibiting herbicides and PPO-inhibiting herbicides, says University of Missouri Weed Scientist Kevin Bradley.

A similar scenario with Palmer pigweed and resistance to PPO inhibitors would be a worst case situation for most cotton growers in the Southeast.

Alan York, now retired North Carolina State University weed scientist and his former graduate student, Stanley Culpepper, now a University of Georgia weed scientist, have been at the forefront of what is now nearly a decade of finding answers to herbicide resistant pigweed.

Though retired, York continues to lead a group of weed scientists from North Carolina State University in their quest to help farmers in the upper Southeast find new, economic and efficient herbicide combinations to fight the overall problem of weed resistance to herbicides.

Charlie Cahoon is a graduate research assistant at North Carolina State University and one of York's latest protégés to take up the fight against herbicide resistance in North Carolina. Under York's leadership, he and other

North Carolina State weed scientists put in a series of tests to develop some alternative systems to popular multiple applications of PPO inhibitors.

For the past three years we've looked at a number of herbicide combinations that reduce dependence on PPO inhibitors, Cahoon says.

“If we lost PPO herbicides, like they have in some parts of the country, it would be a scary thing for North Carolina cotton growers. About all we would have left is glufosinate and over a period of years of overuse we could lose that to resistance problems, too,” he warns.

Glufosinate, sold by the tradename Ignite, and more recently, Liberty is a broad-spectrum postemergence herbicide that has no soil activity. Ignite inhibits the activity of the glutamine synthetase enzyme that is necessary for the plant to convert ammonia into other nitrogen compounds.

Glufosinate resistant (Liberty Link) crops with an alternative glutamine synthetase enzyme have been developed through genetic engineering.