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2-1-2: Is it a valid approach to resistance management?  
by
Bob Hartzler and Mark Loux

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October 03, 2007  

Introduction: Syngenta recently initiated an ‘educational/promotional’ campaign endorsing an herbicide resistance management strategy they have named 2-1-2. The numeric code describes an approach where no more than two applications of glyphosate are made to one field in a two year period. This approach to resistant management is different than those typically recommended by land-grant universities. Extension Weed Scientists Mark Loux (The Ohio State University) and Bob Hartzler ( Iowa State University) express their views on the merits of 2-1-2 in the following dialogue.

Mark Loux: Bob, this ad is part of Syngenta’s continuing quest to be perceived as taking the high road on glyphosate stewardship, and I guess they should be acknowledged for maintaining awareness of resistance issues. However, they have tried to oversimplify a fairly complex issue here. Taken at face value, the 2-1-2 strategy doesn’t work. Using this strategy, a producer could make two glyphosate applications in Roundup Ready soybeans, and then use herbicides other than glyphosate in corn the following year, and so forth. The problem – producers in Ohio developed glyphosate-resistant horseweed (marestail) populations with exactly this program.

Bob Hartzler: One of my mottos is “Simple is good”, and that’s why I kind of like this approach. Weed scientists in the North Central Region developed an extension bulletin on herbicide resistance back when ALS resistance was first emerging as a problem. In order to keep everyone happy, they ended up with a list of ten strategies to avoid resistance – the list was so big that I think the important points were lost among the clutter. 2-1-2 may not be perfect, but I think it addresses the key point in resistance management – you need to limit your reliance on glyphosate.

Mark: The simple approach does not work in this case. Limiting reliance on glyphosate is certainly one strategy in resistance management, but the horseweed example shows the additional importance of using herbicides other than glyphosate in Roundup Ready systems. The key to avoiding glyphosate resistance in marestail in Ohio appeared to be the use of 2,4-D with glyphosate in preplant treatments to soybeans, along with crop and herbicide rotation. Avoiding the use of glyphosate every other year slowed but did not prevent the development of resistance in the absence of other strategies.

Bob: Hindsight is always 20:20 (how many clichés can I work into this argument?). I see your point, but question where to go with it. Are you suggesting that we always add something to glyphosate to manage resistance selection? If so, what product, and what about the cost? Since we don’t know the next weed likely to evolve resistance, I don’t know what alternative product to tell farmers to use in combination with glyphosate. They can’t afford to go with a full rate of a broad-spectrum product since they’ve already invested in the technology fee and the cost of the postemergence glyphosate application(s). Thus, they’re shooting in the dark by using an inexpensive treatment that might or might not reduce selection pressure on that ‘next’ glyphosate resistant weed. That’s why I think its important to avoid continuous planting of Roundup Ready crops, and the 2-1-2 strategy pretty much accomplishes that.

Mark: I agree that continuous use of Roundup Ready crops places producers at greater risk of resistance. But, how does the 2-1-2 strategy prevent this? Unless I missed something (in which case Syngenta’s ad has failed as well as their approach), producers could still plant Roundup Ready continuously, and use an application of glyphosate every year. In a recent article on your website you highlighted an Australian study that showed there is indeed merit to taking steps to reduce the risk of glyphosate resistance, or at least slow its development. Your article lacked any of that biting commentary you do so well, so it appears that you agree with the authors. So, let’s get producers thinking about what the best approach is. I don’t think it has to be complex, but the bottom line is that we need to combine several strategies to do it effectively. Because we don’t know which weed is likely to become resistant next, we can’t determine which one strategy would work for a given weed species. Promoting an overly simple approach isn’t going to help. Another Australian weed scientist, Steve Powles, has come to the same conclusion based on his experience with glyphosate resistance – producers need to use as many strategies as possible in the hope that they all add up to slow the development of resistance (if all else fails, mention the name of another notable weed scientist – my integrated approach to debate).

Bob: Damn, I hate it when someone leaves me speechless. I’ll agree with you that it is too complex a problem for such a simple solution. However, I do think the 2-1-2 strategy would prevent the majority of Iowa farmers from growing continuous RR crops since most use two applications of glyphosate in their soybeans. Thus, the 2-1-2 is a good start, but we need to go beyond that.

Mark: Maybe we just need to get Syngenta to change the ad to “2-2-2”. Over a 2-year period: two different crops - Roundup Ready vs other; no more than two applications of glyphosate; and two different sites of action on each weed species each year. I’ll be waiting for my royalties on this (a long time probably).

 

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.