The Need for Herbicide Stewardship

Micheal D. K. Owen, Faculty, Agronomy Department


Weeds continue to remain the principle pest problem plaguing Iowa production agriculture.  Currently, transgenic corn and soybean, specifically cultivars that are resistant to glyphosate, dominate Iowa production.  As a result, growers tend to us only glyphosate when controlling weeds.  This has dramatically increased the risk of selection pressure which will result in weed population shifts or the evolution of glyphosate resistant weed biotypes.  Furthermore, given that glyphosate can kill larger weeds, growers tend to delay applications such that significant loss of potential yield is incurred.  ISU Extension has an obligation to provide clientele with information about risks related to various agricultural technologies and the adoption of these technologies.  ISU Extension is the sole source of objective information for Iowa agricultural endeavors and thus has an obligation to develop and deliver information that is important to the well being of Iowa Agriculture.


Develop and deliver objective information describing the implications of various crop production and weed management technologies on the evolution of herbicide resistant weed populations and potential crop yield.  Specifically, the implications of transgenic crops and the use of glyphosate will be the focus of these efforts.  Glyphosate resistant weed populations can impact crop yield and crop production expenditures, and potentially can depreciate land values.  Importantly, delayed glyphosate applications result in significant loss of crop yield potential.


The dissemination of information will be via traditional strategies (grower meetings, AgChem dealer meetings, short courses, conferences, publications, and popular press/radio offerings) and via web-based education tactics.  Also, a national glyphosate stewardship effort continues to address issues of stewardship and IPM practices.  An international stewardship forum is planned for October 2008.  ISU Extension Weed Science continues to provide valuable science-based objective information about herbicide stewardship for Iowa growers.

Outcome Statement:

Short-term results measure awareness and knowledge.  Growers will demonstrate a high knowledge level about the implications of the evolution of glyphosate resistant weed populations and weed population shifts.  Furthermore, growers will understand the implications of weed management tactics on crop yield and profitability.  Growers have increased the use of alternative weed management tactics on 40 to 60% of the crop acres in Iowa.  It is estimated that current weed management tactics are resulting in 5 to 10% loss of potential crop yields. Thus, adopting stewardship will result in considerable return on investment.

Medium-term results measure behavior change.  Growers will begin to understand weed populations dynamics and the implications of weeds on crop yields.  They will adopt more effective weed management practices.  The AgChem industry will promote more effective weed management programs and incorporate stewardship practices in their marketing of proprietary products.  AgChem Dealers and growers will make more effective use of available weed management tactics and incorporate alternative strategies on 90% of the crop acres in Iowa.

Long-term results measure condition (i.e., new standard).  Stewardship of herbicides and weed management will result in more consistent and profitable crop production and deter the evolution of herbicide resistant weeds and weed population shifts.  Better IPM practices will be incorporated into crop production.  Higher crop yields and lower input costs for weed management will result from the stewardship programs. 


100 Corn and Soybean Production

Page last updated: August 25, 2008
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