Weed glyphosate resistance is on the rise in South Dakota’s fields, says SDSU Extension Weed Specialist, Mike Moechnig, during a recent iGrow Radio Network interview.
 
Moechnig says waterhemp tops the list, followed by kochia.
 
"We’re seeing more confirmations of waterhemp resistance; but also kochia. Kochia is actually almost a bigger problem in Central South Dakota and even a more challenging weed to control than waterhemp if we don’t have glyphosate as an option," Moechnig said.
 
He adds that other weeds building resistance to glyphosate include; common ragweed and for no-tillers horse weed or marestail.
 
Moechnig says the key to managing glyphosate resistance is to find the problem early, before the seed bank has a chance to build up.
 
"You want to be watching for a patch that is not being controlled or any particular area of the field where a few weeds are surviving, but most are not," Moechnig said. "Often people wait before adjusting their weed management program as they think it’s the weather, or they think it’s something else and before they know it they have a high seed bank and it becomes a real challenge to start depleting that seed bank again."
 
To prevent glyphosate resistance or manage resistance once it occurs, Moechnig advises diversity, both with herbicide modes of action and rotation.
 
"There are several great options to increase the consistency of weed control in the short term and minimize glyphosate resistance in the long term," he said.
 
Moechnig suggests rotating corn and soybeans or other crops, and to use soil residual herbicides in corn fields and consider tank mix partners in soybean fields. Pre-emergence herbicides in corn can minimize early season weed competition which can prevent corn yield loss and tank mix partners in soybeans can increase the consistency of weed control.
 
"Bottom line is to diversify in any way possible," Moechnig said.