Urbana, Illinois
July 10, 2007
Genetically modified seeds that
are resistant to a low-toxicity herbicide, glyphosate, have a
positive environmental impact when compared to other
technologies to combat weeds, according to a recent
University of Illinois
(UofI)study.
"With the emergence of glyphosate-resistant (GR) weeds, the
environmental consequences of alternatives to the use of
genetically modified seed are of increasing importance,"
explained Gerald Nelson, a professor in the U of I Department of
Agricultural and Consumer Sciences.
Nelson and his doctoral student Justin G. Gardner conducted a
study that simulated the environmental effect of abandoning the
glyphosate-resistant seed if weeds develop immunity to it. They
utilized a well-known mammalian toxicity measure, the LD 50 dose
for rats (the volume of pesticide needed to kill 50 percent of a
test population of rats), to assess one potential environmental
impact. They simulated the consequences for corn, soybeans, and
cotton.
"With conventional tillage, we found that the use of GR seeds
reduces the number of LD 50 doses applied per hectare by 17
percent to 98 percent, depending on the crop," said Nelson.
"With no-till, the use of GR seeds reduces LD 50 doses only in
corn.
"If farmers switch to conventional seeds because of GR-resistant
weeds but maintain the same tillage practices, our simulation
suggests that LD 50 doses could increase by as much as 100 LD 50
doses per hectare in soybeans, and 500 LD 50 doses per hectare
in cotton, or 11.4 and 19.8 percent, respectively."
Reducing LD 50 doses per hectare generally depends on the crop
and whether the tillage system changes.
"Because no-till replaces mechanical weed control with chemical
weed control, we expect it to increase the LD 50 doses as in
fact it does for all three crops, even with the use of GR
seeds," Nelson noted.
The simulation assumed the extreme case of all farmers switching
to non-GR seed technology. Nelson added that due to the small
number of farms that use GR seed in the sample, the corn results
are suspect.
Recently summarized in Science magazine, available at
www.sciencemag.org/cgi/content/full/316/5828/1116, the
detailed results are available in a paper forthcoming in the
Journal
of Pest Management Science.
Author: Bob Sampson |
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