Greensboro, North Carolina
November 9, 2005
Source:
Syngenta Crop
Protection
Over the past couple of months, news and
perspectives on glyphosate weed resistance management have made
headlines. While the development of herbicide resistance may be
inevitable, the question remains - what is the best approach to
prolong the viability of one of the most valuable herbicides
known to agriculture?
From growers, retailers and university personnel,
the discussion takes various perspectives. An interesting debate
between researchers at Iowa
State University and the Ohio
State University on the merits of Syngenta’s 2-1-2
glyphosate weed resistance management strategy was recently
posted on the website of Iowa State University at
http://www.weeds.iastate.edu/mgmt/2005/2-1-2.shtml.
Source:
Iowa State
University
2-1-2: Is it a valid approach to resistance management?
by
Bob Hartzler
and Mark Loux
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
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