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.