Weed management has changed dramatically in the last 10 years. Since the introduction of glyphosate-resistant (Roundup Ready) soybean in 1996, varieties with the Roundup Ready trait have been grown on an increasing number of acres, totaling more than 65 million acres in the US in 2004 (Anonymous, 2005). Corn hybrids with the Roundup Ready trait have also increased in popularity since their introduction in 1998, and were planted on more than 8 million acres in the U.S. in 2004 (Anonymous, 2005). With this dramatic increase in Roundup Ready trait acreage, glyphosate use for in-crop weed management has also increased, and will likely increase further with expected increases in Roundup Ready corn and alfalfa acreage. Although glyphosate offers the perceived benefits of safe, simple, and effective weed management to growers, it is subject to many of the same pitfalls as other herbicides, including resistant weeds.