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Multiple herbicide groups work!!
by Bob Hartzler

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April 2, 2015 - Researchers at the University of Illinois recently published results of a project evaluating factors influencing the evolution of glyphosate resistant (GR) waterhemp. The study involved several hundred fields across a 300 sq. mile area in south central Illinois. They collected seed from waterhemp present in the fall of 2010. The presence of GR waterhemp was determined in greenhouse screening. Relationships between glyphosate resistance and past management practices (2004-2010), soil characteristics, and landscape features were determined using a variety of statistical tools.

As one would expect, herbicide use patterns had the greatest impact on glyphosate resistance. Using mixes of multiple herbicide groups was the most effective method of delaying resistance evolution. For example, fields that averaged 1.5 herbicide groups/year between 2004-2006 had an 80% likelihood of having GR waterhemp, whereas the likelihood of having GR was less than 15% in fields that averaged 2.5 herbicide groups/year.

Rotating glyphosate use from year to year provided little benefit in preventing glyphosate resistance. The presence of GR waterhemp in adjacent fields also had little influence on the presence of resistant waterhemp. Thus, implementing programs using multiple herbicide groups was effective at both reducing selection of GR waterhemp from within the field and at preventing the movement of GR from adjacent fields into the field.

The authors stressed that using mutliple herbicide groups is only a temporary fix for herbicide resistance. Diversified weed management programs that include chemical, cultural and mechanical control are needed to sustain our current cropping system.

Evans, J A, P J Tranel, A G Hager, B Schutte, C Wu, L A Chatham, and A S Davis. 2015. Managing the evolution of herbicide resistance. Pest Management Science doi: 10.1002/ps.4009


Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University

For more information contact:
ISU Extension Agronomy
2104 Agronomy Hall
Ames, Iowa 50011-1010
Voice: (515) 294-11164

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Common chemical and trade names are used in this publication. The use of trade names is for clarity by the reader. Inclusion of a trade name does not imply endorsement of that particular brand of herbicide and exclusion does not imply nonapproval.