13. Glyphosate use races through the Midwest, reaching a point where today it is used on 95% of U.S. soybean acres and 65% of U.S. corn acres. Predictably, resistance races across the Midwest.
The first glyphosate-resistant waterhemp biotype in the Midwest is found in Missouri in 2005. In 2008, a survey of 200 Iowa common waterhemp populations shows one third resisted glyphosate. That number has increased since then, says Owen.
14. Resistance tip: Use different systems. Arkansas farmers are starting to rotate between Roundup Ready soybeans, LibertyLink soybeans, and conventional soybeans, says Bob Scott, University of Arkansas Extension weed specialist. “This breaks the cycle of continuous Roundup use,” he says.
15. Resistance woes compound when a weed biotype resists multiple herbicide modes of action. In 2005, weed scientists identify triple-stack resistance of glyphosate, PPO inhibitor, and ALS inhibitor resistance in waterhemp. By 2009, quad-stack resistance to glyphosate, ALS inhibitors, triazines, and PPO inhibitors to an Illinois waterhemp biotype is identified. By 2009, HPPD-inhibitor resistance surfaces in both Iowa and Illinois in triple stacks with other modes of action.
16. Resistance tip: Jump off the transgenic treadmill. Promising new technology – featuring soybean tolerance to dicamba, 2,4-D, and HPPD inhibitors – is slated for later this decade and will join Roundup Ready and LibertyLink systems. Just don't get stuck on one type as you did with Roundup Ready.