2-Plants: Linkages between resistance problems, resistance management and GE crops?
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----------------------------- GENET-news -----------------------------
TITLE: Linkages between resistance problems, resistance management
and genetically modified crops?
SOURCE: PAN Germany, by Crescentia Freudling
summary of lecture at PAN Europe meeting 1999
DATE: March 2000
-------------------- archive: http://www.gene.ch/ --------------------
Linkage among resistance problems, resistance management and
genetically modified crops?
(presented at the PAN Europe Meeting 1999 - Pesticide Reduction, Time
for Action, 30.9. - 2.10.1999 in Hamburg)
The issue of pesticide resistance is linked to pesticide reduction
through the fact that insecticide and herbicide resistance in insects
or weeds commonly correlate with higher pesticide usage and higher
The many discussions of Bt resistance management plans (i.e. high
toxin production in the Bt plants and the percentage of non-Bt plants
grown in refuge fields) by public researchers and NGO persons
generally neglect the vast knowledge and practical experience of
resistance management strategies gained from sprayed insecticides,
fungicides and herbicides. It is a fact that until now, with
pesticides, there have been many more resistance management failures
The risk factors highly influencing the selection of herbicide
resistant weeds are known and published: no crop rotation, no
ploughing, only chemical weed control, the herbicides used with only
one biochemical mode of action. Therefore a combination of "three Rs"
is recommended to prevent weeds becoming herbicide resistant or to
solve herbicide resistance problems. The rotation of crops, rotation
of cultural practices (ploughing included) and a rotation of the
modes of action of the used herbicides are advised.
Information on resistant weeds: new glyphosate resistant weeds
There is a very informative and freely accessible documentation of
herbicide resistant weeds worldwide (www.weedscience.com). It seems
this databank is neither widely known nor used by NGOs. Namely, two
more cases of glyphosate resistant weed species, proven and published
in 1999, have gone undetected: a glyphosate resistant rigid ryegrass
(Lolium rigidum) in California/USA and a glyphosate resistant
goosegrass (Eleusine indica) in Malaysia (at the homepage of
weedscience.com please select "mode of action", then choose
"glycines" and you will find the examples). In all likelyhood these
two resistant weeds have been selected in no-tillage field systems.
Genetically modified crops are grown for resistance management
The databank presents a summary table of herbicide resistant weeds
worldwide. In this summary 58 weed species and biotypes resistant to
ALS inhibitor herbicides (such as imidazolinones, sulfonylureas,
triazolopyrimidines) in 16 countries have climbed to position two,
next to 61 triazine-resistant weeds in 22 countries; in November 1999
they took the lead. ALS inhibitor resistant weeds are most
problematic in cereal, corn/soybean (!!), and rice production. It is
likely that they will present farmers with greater problems in the
next five years than triazine-resistant weeds have caused in the past
By analysing and compiling databank information on the first proven
occurence of weeds in soybean fields being resistant to ALS inhibitor
herbicides in US states (Arkansas, Iowa, Minnesota, Ohio and others),
I am able to conclude that these resistant biotypes should cause
substantial problems for weed control. Consequently it follows that,
in the USA, Roundup Ready soybeans are introduced and planted for
weed resistance management purposes. Farmers switch from the overused
herbicidal mode of action B (ALS inhibitor herbicides which resulted
in resistant weeds within a few years) to the herbicidal mode of
action G which is glyphosate, a chemical whose resistance risk is
But by doing only one rotational step, i.e. replacing imazethapyr,
imazaquin, imazapyr, chlorimuron-ethyl and other ALS inhibitor
herbicides in soybean with glyphosate sprayed on to genetically
modified Roundup Ready soybean varieties, US farmers will hardly
solve the problem. They will indeed spray their acres quickly into
the next weed resistance catastrophy. Glyphosate resistant weeds will
be selected easily from the increased glyphosate usage as many fields
with a no-tillage history already have often a long field history of
glyphosate usage. In the least, to my opinion, glyphosate resistant
weeds will develop because of out-crossing transgenes.
It can be shown that in the USA and in China genetically engineered
Bt-cotton is also introduced and "needed" for resistance management
- The link between resistance problems and the newly grown
genetically modified crops should be adressed seriously and properly.
- The US agriculture is no model! To quote experts of the herbicide
industry: "From experience, we can conclude that rotation of
herbicides alone is not enough to prevent the development of
resistance." The USA should introduce integrated weed resistance
management practices immediately!
- All interest groups, NGOs included, should become involved in
acquiring knowledge on resistance management and resistance
prevention because resistance problems, IPM measures, the quantity of
pesticide usage and pesticide dependency are closely interlinked!
A more detailed version of these arguments (with six tabels and
reference literature) is available on request from the author or the
PAN Germany bureau!
| GENET |
| European NGO Network on Genetic Engineering |
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