Weed resistance issues were top of mind for many farmers attending the 2012 Commodity Classic held last week in Nashville, Tenn. The media heard plenty about it at a couple pre-conference events.

University of Tennessee’s Larry Steckel spoke to 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 that day – 80,” 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 at 2 in. in height. But just 24 hours later when pigweed is 4 in. tall, glyphosate will control only 75% of the weed population. With only 75% control, farmers will not be able to combine the fields.

Later, a farmer at the event said he has heard of landlords losing their renters because of severe weed resistance in the fields. Land also has been sold at a discounted price if there are heavy populations of resistant pigweed on it.

Multiple resistance

If growers from the northern states think they are safe from the weed resistance issues, they need to think again. Jeff Stachler, extension weed specialist in Minnesota and North Dakota, has documented a serious spread of resistant weeds through these northern growing areas. 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.”

In fact, he says they may have identified ragweed and waterhemp with three-way resistance in Minnesota and North Dakota. The resistance is to glyphosate, ALS inhibiting and PPO inhibitor herbicides.