http://live.psu.edu/story/48259
Growing Roundup-Resistant Weed Problem Must be Deal with, expert says
EDITED

When Penn State weed scientist David Mortensen told members of the
U.S. House Oversight Committee this summer that the government should
restrict the use of herbicide-tolerant crops and impose a tax on
biotech seeds to fund research and educational programs for farmers,
it caused quite a stir.

Mortensen, he professor of weed ecology in the College of
Agricultural Sciences, has spent his career researching weeds that
affect agricultural production, sustainable ways to control them, and
the relationships between crops, native and invasive weeds, and
pollinators. He has published several peer-reviewed papers on the
subject in recent years.

The resistant weeds cannot be killed by the sole use of glyphosate,
the active ingredient in Roundup herbicide. The weeds now infest
about 11 million acres -- a fivefold increase in three years,
Mortensen reported.

This list includes many of the most problematic weed species, such as
common ragweed, horseweed, johnsongrass and several of the most
common pigweeds -- many of which are geographically widespread.

Mortensen expressed concern about herbicide- and
germplasm-development companies responding to the
glyphosate-resistance problem by developing a new generation of
genetically engineered crops in which glyphosate-resistant cultivars
are being engineered to have additional resistance traits introduced
into the crop's genome. "These additional gene inserts will confer
resistance to other herbicide active ingredients, including 2,4-D and
dicamba," he said. "For a variety of reasons, it is quite likely that
such crops will be widely adopted. Disturbingly, that would result in
a significant increase of older, higher use-rate herbicides in
soybean and cotton production.
"If they are adopted in the way I expect they will be, herbicide use
in soybean production would increase by an average of 70 percent in a
relatively short time after the release of these new genetically
engineered, herbicide-resistant cultivars."

Vapor drift of more toxic herbicides has been implicated in many
incidents of crop injury and may have additional impacts on natural
vegetation interspersed in agricultural landscapes, Mortensen told
lawmakers. Scientists have documented that nontarget terrestrial
plant injury was 75 to 400 times higher for dicamba and 2,4-D,
respectively, than for glyphosate.

Together the herbicide and seed-breeding industries are moving to
address the problem of resistance with crops that have been
engineered to be resistant to multiple herbicide active ingredients,
according to Mortensen. If these new crop introductions occur as
reported, we should expect to see herbicide use continue to increase
and a significant proportion of those added herbicides will be older,
less environmentally benign compounds, he predicted.

"Biotech companies are trying to deal with the problem by engineering
new crop varieties that will be immune to more than one herbicide,
but even those products will eventually run into resistance problems
if farmers aren't careful," he said.

"Transgene seed and associated herbicides should be taxed and
proceeds used to fund and implement research and education aimed at
advancing ecologically based integrated weed management," he
concluded.

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