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The Green Guide

Monsanto's Frankencrops Give Rise to Herbicide
Resistant Superweeds

Does Roundup-resistant marestail illustrate problems
with reliance on GM crops and pesticides?

(February 22, 2001 --Crophchoice news) -- Scientists discovered
glyphosate-resistant marestail (horseweed) in three fields of Roundup
Ready soybeans in Delaware. The resistant weeds may be present in
other fields there, and in New Jersey and Maryland, as well.
Glyphosate is the active ingredient in the herbicide Roundup, which
Monsanto has engineered its Roundup Ready soybeans to resist.

"It certainly looked like resistance," University of Delaware weed
scientist Mark VanGessel told Farm Chemicals magazine. "Marestail
control was random throughout the field, which ruled out sprayer
problems or applicator error. With almost ideal weather conditions
early in 2000, we also ruled out environmental or stress factors."

Members of the agricultural community disagree about the implications
of this finding.

VanGessel dismissed the idea that Roundup Ready soybeans transferred
their herbicide resistant genes to the marestail.

"Weeds go through frequent genetic changes," he said. "It's random
chance that the marestail developed resistance to Roundup."

To deal with the problem, he suggested that growers spray 2,4-D (in
combination with other herbicides) at least seven days before planting
their soybeans. Then, after the Roundup Ready soybean plants have
emerged, growers can spray Roundup to control the other weeds.

Others in the agricultural community contend that doing this points
out the irony of escalating herbicide use at a time when the
biotechnology industry is telling farmers that its genetically
engineered plants require fewer herbicide applications.

Agricultural economist and consultant Charles Benbrook admitted that
he couldn't address when the marestail resistance to Roundup emerged,
but he does think that Roundup Ready crops "pushed it over the edge."

Since 1996, when industry first bioengineered crops for widespread
commercialization, herbicide use has increased, Benbrook said.

"Of course Roundup resistant weeds can be sprayed with other
herbicides," he said. "If that is the solution, what about those
cost-savings to farmers and reductions in soybean herbicide use?"

"2,4-D goes on soybeans at about 0.4 pounds (active ingredient) per
acre. Add in two applications of Roundup at the average 0.7 pound
rate, and a grower is applying just under 2 pounds of herbicide per
acre." No-till growers and some others apply Roundup three times, he
said. This practice will grow more common as generic competition
drives down the price of the herbicide.

Add to that the .2 to .5 pound of herbicide (again, active ingredient)
that most growers are applying per acre just before or when they sow
their seeds, he said.

In 1999, biotechnology and chemical conglomerates aggressively
marketed 13 combinations of low-dose herbicides for use on
conventional soybean plants, he said. (The average application rates
for these herbicides are less than 0.1 pounds active ingredient per
acre, based on 1999 USDA chemical use survey data for soybeans). One
of the very low dose herbicides - thifensulfuron -- is applied at
0.002 pounds active ingredient per acre; growers sprayed it on 5
percent of the nation's soybean acreage in 1999.

In 1998, he said, growers applied an average of 1.4 pounds of
herbicides (.92 pounds of glyphosate and .5 pounds of other
herbicides) to genetically modified soybeans. Plus, Roundup Ready
soybeans required about 40 percent more active ingredient per acre,
measured by weight, than non-bioengineered soybeans.

In contrast, the average acre of conventional soybeans in 1998
required about 1 pound of herbicides.

Benbrook's conclusion is that Roundup Ready soybeans, on average,
require much more herbicide per acre than non-bioengineered varieties.

"Roundup Ready technology has its virtues but sustainability and
reducing herbicide use are not among them," he said.

Marestail is not the first weed to develop resistance to Roundup,
which is interesting given that the biotechnology industry has long
said it's impossible for weed species to develop such a trait, said E.
Ann Clark, a pasture and grazing specialist at the University of
Guelph in Ontario, Canada.

Three years ago, rigid rye grass in Australia developed resistance to
Roundup after a farmer had applied too much of it. And on a Malaysian
plantation, goose grass (one of the 20 worst weeds in the world)
showed resistance, she said, noting that the tolerance was specific to
that location.

Although the evidence is only anecdotal, Clark has heard reports from
western Canadian farmers of weeds developing resistance to the
herbicide 2,4-D, an endocrine disruptor.

"Overreliance on any single method of weed control will select for
individuals tolerant to that method of weed control and Roundup is no
exception," she said.

Purchasing expensive genetically engineered seeds and herbicides has
increased the cost of production for farmers. The problem is not the
crops themselves, but the way that we're growing them, she said.
Planting corn, soybeans, and corn, year after year, and then spraying
them with the same herbicides at the same time leaves a niche for
weeds to grow and develop resistance.

Clark suggests that grain and livestock producers should instead plant
winter cereals as part of a more complex crop rotation. This, combined
with lessening or eliminating the use of herbicides, will reduce their
production costs, widen their margins, and yield a higher net profit.