Features Agronomy Weeds
Weed Science Society warns herbicide-resistance increasing

June
5, 2008

Glyphosate, a herbicide which is marketed
under various names, is widely used around the world to control a broad array
of weeds in agriculture, forestry, orchards, rights-of-way and around the home.

Glyphosate is an especially effective and
simple weed management tool for some agricultural crops that can tolerate the
herbicide. However, its widespread, repeated, and often sole use for weed
management has selected weeds that have become glyphosate-resistant and are
thus not controlled by this herbicide.

The Weed Science Society of America promotes
the responsible use of a variety of weed control measures and cautions against
following a single approach to weed management, which can result in resistant
weeds.

In the past, farmers applied herbicides that
controlled weeds without harming their crops. Typically, a herbicide is
effective only on a specific, limited set of weed species. Therefore, farmers
often needed to use two or three different herbicides or apply them more than once
to control the assortment of aggressive weeds that sprang up in their crops.

Glyphosate became a prominent herbicide in
agriculture about 12 years ago when it was discovered that
glyphosate-resistance genes could be inserted into crops using biotechnology.

Now, glyphosate-resistant corn, cotton,
soybeans, canola and sugarbeets are common. This means farmers can spray these
crops with glyphosate to kill most or all unwanted weeds while their crops
remain unharmed.

Glyphosate thus became the dominant weed
control method on many farms, and quickly replaced other weed-fighting tools
and tactics.

“Glyphosate is easy to use,” says Chris
Boerboom, University of Wisconsin Extension
Weed Scientist and Weed Science Society of America member. “Glyphosate’s
effectiveness as a broad-spectrum herbicide left many growers relying on it
frequently and even exclusively in their battle to control weeds.
Unfortunately, once a naturally resistant weed appears in a field, it can
escape and multiply into a serious problem in the next few years.

“Over the past several years, we have seen the
list of glyphosate-resistant weeds grow to nine species, which are scattered
across at least 20 states. Farmers are being challenged to control
glyphosate-resistant weeds like Palmer amaranth (Amaranthus palmeri) and giant
ragweed (Ambrosia trifida) in certain crops. We urgently need to slow the
development of resistance before glyphosate’s value to farmers is diminished.”

“The Weed Science Society of America
encourages farmers to continue using a diverse set of tools to manage weeds.
These tools include using different herbicides that can control these weeds,
along with nonchemical weed control measures, in rotation or combination with
glyphosate,” says Boerboom.

The Weed Science Society of America advises
policy-makers, agricultural and natural resource managers, and educates the
public on issues related to the control and management of weeds and invasive
plants. The overall effects of weeds and invasive plants on the nation’s
agriculture, water quality, wildlife and recreation have been estimated to cost
the U.S. $34.7 billion annually, according to a recent Cornell University report.

For more information about glyphosate
resistance, contact Lee VanWychen, Director of Science Policy for the Weed
Science Society of America, at 202-746-4686 or visit www.wssa.net.