SnowBall archive


GE - GM herbicide resistant crops fail to deliver economic benefits in US

(For those who wish to provide internet links to it this commentary is
as a web page at

Set out below are important extracts from a paper presented at the 1997
British Crop Protection Conference in Brighton, England, on "North American
Developments in Herbicide Tolerant Crops" by M D K OWEN, of
Iowa State University.

The paper concludes that the use of herbicide resistant crops, including
genetically engineered varieties, are unlikely to provide farmers with
economic advantages over existing weed management strategies.  The full
paper can be viewed at

Although this paper dates from 1997 it has since become clear from other
reports that agronomists in the US are now advising growers of Roundup Ready
soya beans, for example, to use multiple applications of glyphosphate on
these crops (or to use residual herbicides in addition to glyphosphate) in
order to achieve intended levels of weed control (see footnote).  This
technology was originally marketed as requiring just a single application of
Roundup but in
many cases this has not given the intended (i.e weed-free) results.

Please note the following before reading the extracts:

1) The paper refers to herbicide resistant crops in general, not just those
which have been genetically engineered for such purposes.

2) Weed resistance to herbicides already commonly develops because of the
over-use of a particular herbicide, through natural selection/mutation of
weed species in response.

This phenomenon already exists whether or not there is an additional risk of
herbicide resistance development in weeds through gene transfer between
crops and related weed

3)  Results from both the 1997 and now the 1998 harvests demonstrate that in
most cases yields from genetically engineered Roundup Ready soya varieties
are lower than non-modified varieties (see footnote).

4)  Total weed kill (a concept promoted by biotechnology companies in
marketing GM herbicide resistant varieties) can often only be achieved by:

        - using a single application of Roundup at a late stage of crop
development resulting in yield losses

        - using multiple applications of Roundup (and/or residual
throughout the life-cycle of the crop

These scenarios have the double disadvantage of producing lower profits for
farmers (through low output or high input costs) as well as destroying farm
biodiversity (see Iowa State University report on potential effects on
Monarch butterfly at
.edu/weednews/monarchs.htm )

5) Because of the lack of objective impartial advice on these matters US
farmers are often unaware of these trade-offs, with the result that both
farm economics and farm environment are frequently worse of than if more
conventional approaches to farm weed management were utilised.

6) Herbicide resistant crops have been marketed to farmers on the basis of
simplifying management.  In practice they often complicate it for those not
prepared to accept yield penalties arising when leaving weed control until
late in the growing season (the latter is the strategy usually necessary for
total weed
kill where only one application of a broadspectrum herbicide like
glyphosphate is to be

7) US farmers have become unnecessarily obsessed with "total weed kill" in
their crops thanks to pressure from their agro-chemical suppliers. UK
research shows that
reduced weed-kill below certain thresholds can be tolerated (depending on
without substantial effect on yield, provided control of weed populations
above such levels is achieved early in the growing season.

In these circumstances it is tempting to describe the prevalence of
herbicide resistant crops in the US as "a victory of marketing over science
and genuine utility". What farmers
usually get to hear about GM crops from their suppliers ("the benefits")  is
not in
practice usually what is delivered (the losses).

Herbicide resistant crops are generally only for those farmers who don't
know how to farm properly or who can't be bothered to.

In the end this role of protecting agricultural incompetence is the sole
"justification" (see footnote)  for taking huge risks with global food
safety and the environment when introducing genetically engineered crops
incorporating such attributes. This role applies both to herbicide resistant
crops as well as those with in-built insecticides (the latter is another
similar but slightly different story - see our web site for more

Messrs Blair and Clinton (and UK farmers) please take note.




Objectively, when considering the use of herbicide-tolerant corn or
soybeans, and the appropriate herbicide, weed management is not conceptually
different than where traditional crop varieties and herbicide programs are
used. However, farmer expectations are considerably greater with the new
technology compared to existing crops and herbicide treatments. Farmers
generally have failed to recognize the changes in management skills required
to effectively use the herbicide tolerant crops. While the herbicide
tolerant crops may have some advantages compared to current practices, their
use also results in acceptance of risks associated with the technology.

Hess (1996) indicates that the risks associated with an integrated weed
management system based on herbicide-tolerant crops are due to a lack of
knowledge about the ecology and biology of the crop and associated weeds.
Farmer expectations for weed control are greater than what the use of these
strategies, in conjunction with herbicide-tolerant crops, will provide.

The author suggests that herbicide-tolerant crops and the resultant use of
specific herbicides will increase the potential for the development of
resistant weed populations, but the technology could also be used
effectively to deter weed resistance. Even if, as suggested by the industry,
there is little potential for resistance to glyphosate to develop in weed
populations (Anon., 1997), selection will still occur resulting in weed
populations that are not effectively managed by the herbicide (Radosevich &
Holt, 1984).

Ideally, herbicide-tolerant crops will improve the use of alternative weed
management strategies. Wyse (1992) and Burnside (1996) suggest that
herbicide-tolerant crop technology will increase the utilization of
alternative strategies for weed management. However, a recent survey
conducted by the Weed Issue Team at Iowa State University, and supported by
the Leopold Center for Sustainable Agriculture, demonstrates clearly that it
is unlikely that herbicide-tolerant crop technology will increase the use of
alternative weed management strategies.

Farmers have expectations for weed control that are unreasonable from an
environmental, ecological, and economic perspective. The herbicide industry
has done an effective job of educating farmers about the level of weed
control herbicides will provide and the consistency that this level of
efficacy will be delivered. As a result, farmers have learned that weed
control is synonymous with weed-free and a zero-tolerance for weed escapes
now exists in much of the Midwest.

The expectation by farmers that herbicide-tolerant crops will improve
potential yields, and thus economics, by eliminating risks of weed
interference is not likely to be realized. Economic models suggest that
herbicide-tolerant crops will not likely impact the economics of crop
production (Tauer & Love, 1989). Typically, the level of weed control
provided by herbicide-tolerant crop management systems is equal, but no
better than conventional systems. Farmers also expect weed control costs to
be reduced when herbicide-tolerant crop management systems are used.
Experience in Iowa suggests that the cost of weed control with the new
technology is similar to existing systems.

In Iowa, herbicide drift complaints were higher in 1997 than in past years
(Charles Eckerman, Iowa Department of Agriculture and Land Stewardship,
personal communication). The increased use of herbicide-tolerant crops and
the resultant herbicide applications possibly contributed to this increase.

Glufosinate-tolerant corn, in conjunction with glufosinate, were positioned
as a strategy to manage problem weeds and for use in no tillage production
systems. Often, the glufosinate was applied in combination with a residual
herbicide. Farmer success was varied, depending on the management skills and
expectations. Performance of glufosinate-based systems in Iowa State
University research was variable depending on the level of weed infestation
and environmental conditions.

Glyphosate-tolerant soybean varieties are viewed by farmers as the answer to
all weed management problems. Monsanto has positioned this technology in no
tillage and narrow row spacing systems and farmers presume that it will
eliminate all risks associated with weed control. In 1996, in Iowa planting
was very late and, as a result most of the postemergence herbicide
applications were applied in late June and July. At this time, most of the
weed germination events had occurred and a single application of a
postemergence herbicide was generally effective.

In 1997, planting occurred early and weed germination required an earlier
application of the postemergence treatments. In many instances, unless
alternative weed management was included, second and third applications were
considered necessary by farmers. Glyphosate-tolerant soybeans allowed these
later applications. Experiences in 1997 suggest that better management
skills are required and often second applications may be needed for
glyphosate-based weed control systems.

The issue of yield potential with glyphosate-tolerant soybean varieties was
also a point of discussion. It is suggested that there is no loss of genetic
yield potential with the glyphosate-tolerant soybean varieties (Harper,
1997) yet farmer complaints from 1996 experiences were in evidence. Further
investigation suggests that many of the reported "low" yields were
attributable to delayed glyphosate applications resulting in weed
interference. As with all postemergence herbicide systems, management skills
are important. The understanding of crop/weed interaction, the impact of the
environment on plant development, and the implications of weed populations
on potential crop loss are critically important for maximizing yield
potential; these are not simple strategies!
One of criticisms about weed management programs based on a single herbicide

is the potential for select resistant weed populations (Duke et al., 1991).
Monsanto has suggested that due to the mechanism of action, weed resistance
will not occur (Anon., 1997). Weed scientist have cautioned that regardless
of whether or not resistance in weeds does develop, population shifts to
weeds that are more tolerant to a particular herbicide or "avoid" the
strategy are likely (Holt, 1994).

Experiences in Iowa during 1997 suggest that these population shifts can
occur rapidly. Common waterhemp (Amaranthus rudis) populations demonstrate
delayed germination and have "avoided" planned glyphosate applications.
Velvetleaf (Abutilon theophrasti) demonstrates greater tolerance to
glyphosate and farmers are reporting problems controlling this weed with the
rates of glyphosate for which they are willing to pay.

Farmers have extremely high expectations for weed control resulting from the
herbicide tolerant crop systems. Importantly, the use of herbicide tolerant
crops and appropriate herbicides is perceived to require lower management
than conventional weed management strategies. Evidence suggests this is not
the case.

Proponents suggest that there will be increased use of alternative
management strategies as a result of the herbicide tolerant crop systems.
However, given farmer expectations and marketing strategies, it is unlikely
that alternative strategies will be used, and in fact, a greater reliance
placed upon herbicides for weed control. When considered objectively, the
use of herbicide tolerant crops as a weed management strategy does not
differ greatly from current strategies.


Here is an additional comment (17 March 1999) on the Roundup Ready situation
in the US from independent agronomist Dr Charles Benbrook who is author of
the book "Pest
Management at the Crossroads," 1996 and and who is the former Executive
Director of the Board on Agriculture for the US
National Academy of Sciences:

"......Every independent set of data, recent analysis of RR beans I have
seen reaches the same conclusion; the technology increases costs somewhat,
but imposes a "price" farmers are willing to pay for the
simplicity/robustness of the weed management system.  Oplinger et al. end
their paper saying: "It is anticipated that soybean growers will continue
to increase acres planted to RR varieties and will sacrifice yield for ease
weed control."  They will also sacrifice some net income per acre.

This is a perfectly rational reason for farmers to adopt the technology;
weed management is probably the number one management challenge all soybean
farmers face.

Monsanto should not be ashamed to cite these reasons in
explaining why the technology is being adopted.  But Monsanto needs to drop
the "feeding the world", "lowering costs", "lowering pesticide use" claims
because they do not hold water and will undermine, further, the reputation
of the corporation, and in so doing feed the already considerable cynicism
abroad about the trustworthiness of this company.....

.....As weed shifts continue in areas planted heavily to RR beans, and as
resistance spreads to additional weed species (the first signs of tolerant
weeds are
appearing in several states), farmers will have to increase rates of Roundup
applications and
intensify use of other active ingredients, to fill gaps in control.  Costs
will rise, the income squeeze will get even worse.

Contrary to a Monsanto scientist's claim on the NPR piece, Roundup
does not kill everything green except for transgenic crop varieties.  If
that were the case, most farmers using RR systems would not be applying at
least 2, and on many farms, three additional active ingredients."

Charles Benbrook                         208-263-5236 (voice)
Benbrook Consulting Services             208-263-7342  (fax)
5085 Upper Pack River Road        [e-mail]
Sandpoint, Idaho  83864                 

Benbrook Consulting Services (BCS) provides a public service to those
working to
advance the sciences and art of  biointensive Integrated Pest Management.

Dr. Charles M. Benbrook is a consultant working on environmental, food
safety and pest management issues.