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Herbicide exploitation
by Bob Hartzler

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August 11, 2000 -   With the exception of ALS-resistant waterhemp, herbicide resistance has not been a major issue in Iowa.  However, the potential for resistance remains a threat due to our increasing reliance on herbicides.  The only way to manage resistance is to avoid over-use of a single herbicide or herbicide group through the development of long-term weed management strategies. 

Australia faces some of the worst herbicide resistance problems in the world and has launched a major research and extension program (Western Australian Herbicide Resistance Initiative) to address this issue.  The following is an abstract of a presentation made at the International Weed Science Congress this past June in Brazil.  It addresses the difficulties in changing the mindset of growers that herbicide resistance is something that can be dealt with after the fact rather than something to manage prior to emerging as a problem.

Proactive versus reactive herbicide resistance management: understanding the economic sense of herbicide conservation versus exploitation. S B Powles, M Monjardino, R Llewellyn, D Pannell (WAHRI)

For world grain crops, across most agroecosystems, herbicides are the preferred weed management tool. In response to persistent herbicide usage and reduced use of non-herbicide tools, herbicide resistance is now a major problem in cropping regions of Australia and North America and is an emerging problem in specific cropping ecosystems in many parts of the world. One commonality across these diverse agro-ecosystems is that the industry and growers, even when knowledgeable about resistance, have chosen to continue exploiting their herbicide resource until resistance develops. Thus, they choose exploitation over conservation and thus managing resistance retroactively not proactively. Uncertainty, economic reality, herbicide marketing strategies and many other factors combine to make exploitation of a herbicide resource an apparently logical decision for both industry and growers. Despite the risk of resistance depriving them of a valuable tool, growers apparently consider it economically rational to exploit a herbicide resource. Similarly, herbicide manufacturers faced with competition, expiring patent life, looming generic manufacturers and other factors almost universally choose to maximise short-term market share. Here, using a bio-economic model created for Australian cropping agro-ecosystems, we examine whether herbicide exploitation or conservation by growers is optimal. The results of this analysis demonstrate that while there is an economic incentive for herbicide conservation, this incentive is not great. When combined with other factors, such as uncertainty, it means that conservation is unlikely to be the preferred grower choice. Even when the grower takes a long term view, there are forces driving decision making for rapid herbicide exploitation rather than longer-term herbicide conservation. This understanding of the economic rationale for herbicide usage decision making is essential for campaigns targetted to achieve proactive herbicide usage aimed to maximise herbicide longevity.

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) 294-1923
Fax: (515) 294-9985
http://www.weeds.iastate.edu
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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.