Will Resistant Weeds Show up in 2011?

Published on: 14:04PM Nov 23, 2010

Chuck Foresman

Weed control problems in many fields are becoming all too common. As the 2010 season progressed, many growers across the Midwest and South were surprised to find that glyphosate – even at high rates – didn’t adequately control giant ragweed, Palmer pigweed, waterhemp or other tough weeds.
As one Iowa retailer put it, “If we would have know there was resistant giant ragweed in this field, the grower would have planned on doing something different.”
It is possible to be prepared to fight weed resistance in 2011 with a proactive, long-term plan. One good indicator of potential future problems was the condition of soybean fields at harvest. Uncontrolled weeds show up fairly clearly from the combine.  There are other signs to help gauge the risk of resistance this coming season. 
Herbicide resistance should be suspected when:
  • Herbicides with the same mode of action have been used year after year.
  • Dead weeds next to live weeds of the same species.
  • A patch of uncontrolled weeds is spreading.
  • Other causes of herbicide failure, such as bad weather, application timing and operator error, have been ruled out.
If resistant weeds are suspected, prepare a diverse weed management plan for next season. Rotate herbicide modes of action, using herbicides with residual activity. Develop a workload strategy that allows for timely herbicide applications, and use full, labeled rates. Customized recommendations are available using the Solution Builder at www.resistancefighter.com.