A population of waterhemp has been found to be resistant to glyphosate, the active ingredient in Roundup herbicide.

"Since the inception of glyphosate-resistant crops in 1996, researchers have said that the onset of weed resistance to glyphosate was not a matter of if but when," says Reid Smeda, University of Missouri agronomist.

His research showed that while glyphosate-based herbicides provide "excellent control over 90% of the targeted plants, there were some survivors." In fact, Smeda noted survivors that were visibly stunted but produced viable seed with Roundup Ultra applications as high as 2 gallons/acre.

Smeda emphasizes, however, that glyphosate remains among the most effective and economical herbicides available.