Weed resistance issues were top of mind for many people attending the 2012 Commodity Classic held last month in Nashville, Tenn. University of Tennessee’s Larry Steckel spoke to members of the media at a Bayer CropScience event about the glyphosate-resistant weed problems in his area.

“On June 21, 2011, I got a lot of calls — 80 of them,” reported Steckel. “Most of the calls were about resistant Palmer pigweed and that’s when it dawned on me just how big of an issue this has become.”

He said growers can manage resistant Palmer pigweed if it is sprayed when the weeds are 2 in. tall. But just 24 hours later when Palmer pigweed grows to 4 in., glyphosate will control only 75% of the weed population. With 25% of the pigweed left, a combine cannot make it through the field.

While the worst resistance problems are seen in the South, resistant weeds are headed north. Jeff Stachler, extension weed specialist in Minnesota and North Dakota, documented a serious spread of resistant weeds through northern growing areas in the last couple years. Speaking at a BASF media event, he said some hot spots have resistant weeds in 75 to 90% of the fields. Resistant weeds include common ragweed, giant ragweed and waterhemp.

“We certainly had a big issue in 2011,” Stachler reported. “But that’s nothing. The real game changer is multiple resistance, which is resistance to more than just one mode-of-action herbicide.” He said ragweed and waterhemp with three-way resistance may have been identified in Minnesota and North Dakota. The resistance is to glyphosate, ALS inhibitors and PPO inhibitors.

With resistant weeds on everyone’s doorstep, it’s time for game-changing weed plans.