Waterhemp, a prolific seed producer, is a menace year in and year out in the Midwest. It continues to wreak havoc on fields, affecting yields and expanding to different parts of the country. Not only is waterhemp reproducing at high rates, it has shown variable tolerance to glyphosate herbicides in several states. And, was recently confirmed glyphosate resistant in Missouri in 2005. Waterhemp has already exhibited resistance to ALS inhibitors, PSII inhibitors and PPO inhibitors.

As no new herbicide modes of action are currently in development, it is critical that practices are adopted to preserve glyphosate technology. Utilizing proper cultural and chemical management practices reduce selection pressure placed on resistant biotypes and can help delay resistance.

Preserving herbicides, particularly glyphosate, involves a well-rounded management program. Rotating modes of action and limiting the frequency of glyphosate applications are key to preserving this intricate part of modern agriculture. Syngenta recommends using a pre-emergence, residual herbicide on glyphosate-tolerant crop acres and 2-1-2 as a resistance management program for corn and soybean growers - no more than two applications of glyphosate on one field over a two-year period . Using cultural and chemical management practices helps to incorporate other modes of action into a program. 

Detailed recommendations and further information about waterhemp can be found at http://www.syngentaebiz.com/dotnetebiz/imagelibrary/waterhemp5_26FINAL.pdf.