News | February '10 | Weeds have tricks up theirt sleeves
Weeds
able to survive the herbicides
modern farmers pour over them have been increasing steadily since the
1980s. Over the last three decades (less than a millisecond in
evolutionary terms), some 300 herbicide-tolerant weeds have emerged
world-wide. Resistance to glyphosate (the active ingredient in
'Roundup' weed-killer) has now soared to 16 weed varieties. The
exponential increase in use of Roundup with the advent of GM 'Roundup
Ready' crops has helped them along nicely. Many of these weeds are a
severe practical and financial burden for farmers.
Biotech
companies are scrambling to
find new technicological tricks to solve the problem of the undying
weeds they created in the first place. With nothing much new in the
pipeline of chemical herbicides, the industry is resurrecting older
ones. Weedkillers which had fallen from favour due their toxicity,
are now reappearing in novel cocktail form. Lest farmers abandon
their GM herbicide-tolerant crops because there's no point in growing
them if the herbicide they resist doesn't work, the biotech companies
are ironically joining forces to develop GM crops stacked with a
number of different herbicide-tolerance genes so that farmers can use
a variety of weedkillers.
What are the
chances that all this
genetic and chemical inventiveness will solve the problem, or will we
just end up with super-weeds resistant to all chemicals?
Weeds don't
have
the benefit of being able to borrowing tailor-made engineered genes
from other organisms, nor the services of a chemistry laboratory.
However, they do have an apparently infinite capacity to adjust
their genome at a rate significantly faster than biotech R&D
can
achieve. Weeds can, for example, multiply their chromosome numbers,
which gives them whole extra sets of genes to call into action while
maintaining balance in the function of the other genes. In the case
of Roundup-resistant weeds, some have solved their Roundup problem by
developing their own Roundup-resistant gene, just like the GM
strategy but without the disturbances from added viral and bacterial
DNA and without the disruption of the wider genome. Some
Roundup-resistant weeds have developed the knack of limiting the
damage to manageable levels by blocking glyphosate's movement and
toxic spread around their tissues. The best tactic yet is seen in
Palmer Amaranth.
Palmer
Amarynth, or
'giant pigweed', is the most dreaded weed. As its nick-name
suggests, it can grow up to 8 feet tall, withstand heat and drought,
and can stop a combine harvester and break hand-tools. One farmer is
said to have spent a futile half-a-million dollars in three months
trying to clear the monster weeds. A single plant produces thousands
of seeds and can take over a field in a year.
As
if things
weren't bad enough, Palmer Amaranth has developed the ability to
overcome Roundup by producing so much of the enzyme which glyphosate
blocks that the weed-killer is overwhelmed. Roundup-resistant Palmer
Amaranth has been found to have created anything between 5 and 160
times the number of natural genes. Unlike engineered constructs, the
extra genes are spread around all the plants' chromosomes and respond
directly to need. In this way, there is no energy wasted, the
interference with other interconnected metabolic pathways is
minimised, and there'e less chance of the genes being lost during
reproduction.
The farmers whose bottom line is suffering from all these tricks of nature are broadly unaware of the depth of the resistance problem. Recent research reported:
“A
survey of farmers from six U.S.
States (Indiana, Illinois, Iowa, Nebraska, Mississippi, and North
Carolina) was conducted to assess the farmers' views on
glyphosate-resistant (GR) weeds and tactics used to prevent or manage
GM weed populations in genetically engineered (GE) crops. Only 30%
of farmers thought GR weeds were a serious issue. Few farmers
thought field tillage and/or using a non-GR crop in rotation with GR
crops would be an effective strategy. Most farmers did not recognize
the role that the recurrent use of an herbicide plays in evolution of
resistance. A substantial number of farmers underestimated the
potential for GR weed population to evolve in an agro-ecosystem
dominated by glyphosate as the weed control tactic.”
The attitude in the farming community seems to be that it's a biotech industry problem and the biotech industry will provide a solution: so they sit back and wait. Surveys have confirmed that farmers do not start weed management until the the problem has actually emerged, and explain:
“Part
of the reason growers do not manage proactively is because most know
other options are still available and expect companies to continue to
provide new technology. Unfortunately, companies are not being as
successful in discovering selective herbicides with new modes of
action as they have been in the past.”
OUR COMMENT
We
have a wide range of non-chemical weed-reducing strategies at our
disposal, including vigilance, crop rotations, crop varieties, crop
breaks with fields left fallow or used for grazing, mechanical
weeding, cultivation, mulching with cover crops or weed residues, and
regular variation of the strategies used. All of these methods are
easy to implement in small-scale farming. However, modern
college-courses for farmers, the biotech industry, and the
massive scale of our food supply system, are not well placed to
include non-chemical weed-reducing strategies in which resistance
would never become a problem.
Weeds
have more tricks up their sleeves
than our cumbersome chemicals can ever match. As the big landowners
and the biotech industry try to fight a futile agrichemical arms race
with Nature, it might be sensible to take control of your own diet:
when it comes to buying food, think small, think local and think
organic.
SOURCES:
-
Resistance is Growing, GM Freeze Briefing, January 2010
-
Gaines et al., 2009, Gene amplification confers glyphosate resistance in Amaranthus palmeri, PNAS
-
GM Crops Facing Meltdown in the USA, Institute of Science in Society Report, 1.02.10