Notes: Glyphosate is the most popular herbicide ever discovered. Its broad spectrum of activity combined with its safe environmental package make it a favorite herbicide choice in many situations on the farm and around the home. Because this herbicide is used on such a wide scale, there has been increased concern about the potential development of weed resistance. Unfortunately at this time, at least 8 weed species around the world have developed resistance to glyphosate. In the United States, populations of horseweed or marestail (Conyza canadensis) rigid ryegrass (Lolium rigidum), Italian ryegrass (Lolium multiflorum) and Palmer amaranth (Amaranthus palmeri) have been found to be resistant to glyphosate (highlighted in blue). It is interesting to note that glyphosate was first commercially available in 1974 but the first case of weed resistance to this herbicide was not reported until 1996 (22 years).