Iowa State University
by Bob Hartzler
May 1, 2003 (Revised May 8) - Monsanto recently mailed a flyer to dealers/farmers that outlines Monsanto's perspective on glyphosate resistance. The title of the flyer is 'MANAGING WEED RESISTANCE', but rather than seriously addressing the problem of herbicide resistance the literature reflects Alfred E. Neuman's philosophy on life: 'What, Me Worry?'. The bulletin emphasizes the well documented fact that the potential for glyphosate resistance is less than that of other herbicides, stating that only two weed species have developed resistance to glyphosate in the U.S. after 28 years of commercial use. Because of these facts, Monsanto suggests that farmers need not consider resistance in developing weed management programs. The bulletin implies that as long as full rates of Roundup are used, resistance will not be an issue ('Dead weeds don't produce seeds').
The fact that the potential for resistance to glyphosate is considerably less than that of most herbicides is well substantiated. However, in the past seven years glyphosate-resistant biotypes have been confirmed in four weed species. These biotypes occur in at least seven U.S. states and in five countries. I will give Monsanto credit for maintaining a consistent message. In a 1995 paper released prior to introduction of Roundup Ready crops, Monsanto scientists stated: "Furthermore, the complex genetic transformations which were required for the development of glyphosate-tolerant crops would be unlikely to be duplicated in nature to yield glyphosate-resistant weeds" (Bradshaw et al. 1995). We now have ample evidence that nature indeed can duplicate the efforts of Monsanto's scientists, and thus it seems a change in philosophy toward resistance management is warranted.
While the bulletin doesn't come straight out and recommend planting continuous Roundup Ready crops (e.g. RR soybeans followed by RR corn), this is strongly implied as a sound management decision. A testimonial by a northern Iowa farmer states that five years of continuous RR crops have not led to any problems with weed escapes or resistance. Monsanto provides data indicating an economic advantage to RR crops, and suggests a farmer would reduce net returns by planting non-RR crops in order to prevent something that may or may not occur.
In addition, the bulletin states that resistance is 'easily and economically managed'. While it is true that we have numerous herbicide alternatives in corn and soybean to help manage resistant weeds, I think this attitude towards resistance is misguided. I'm sure many farmers in southern Iowa would state that controlling ALS-resistant waterhemp prior to the introduction of RR soybeans was far from easy and economical, and I knew many Pennsylvania farmers who felt the same way about triazine-resistant pigweed and lambsquarter in the 1980's. When glyphosate resistance develops in Iowa, there will be a real cost to those growers who must deal with glyphosate-resistant biotypes.
Although glyphosate has been marketed for 28 years in Iowa, it is important to remember that Iowa farmers have only used it in a manner that places significant selection pressure on our major weeds since the introduction of Roundup Ready soybeans in 1996. Almost all weed scientists agree that the evolution of resistant biotypes is inevitable with the current use pattern of glyphosate. Increased adoption of rotations relying solely on RR crops will greatly enhance the rate that resistance evolves. Because of this, we feel it is best to develop long-term weed management plans that reduce the selection pressure placed on weeds by any single herbicide, including Roundup.
1Alfred E. Neuman is the feature character of Mad Magazine, and is a copyright of Warner Brothers.
Citation: Bradshaw, L.D., S. R. Padgett, and B.H. Wells. 1995. Perspectives on the potential of glyphosate-resistant weeds. WSSA Abstr. 35:66.
Acknowledgement: I appreciate the diligence of the Missouri dealer who FAX'ed me this promotional piece. The revisions were initiated by the comments of a foreign dignitary who thought the original version wasn't critical enough of Monsanto's position.
Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University
more information contact:
ISU Extension Agronomy
2104 Agronomy Hall
Ames, Iowa 50011-1010
Voice: (515) 294-1923
Fax: (515) 294-9985
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