Officials from the Weed Science Society of America (WSSA) report that nine weed species in the U.S. now have confirmed resistance to glyphosate. Among these weeds are strains of common ragweed, common waterhemp, giant ragweed, hairy fleabane, horseweed, Italian ryegrass, johnsongrass, Palmer amaranth and rigid rye-grass. Over the past 13 years, glyphosate has been applied to more than a billion acres.

“The challenge now is to adopt effective management techniques to keep resistance from spreading,” says David Shaw, WSSA president.

In a four-year research project in six key ag states, researchers are comparing the economics of university-recommended herbicide resistance management programs with the use of glyphosate as an exclusive treatment for weed control.

Third-year results show the net returns on fields managed according to recommended best practices are equal to or greater than the returns on those where glyphosate is used alone. Increased yields appear to offset any increase in herbicide costs.