Glyphosate resistance was first reported in 1996 from rigid ryegrasss in an orchard in Australia. Subsequently, several additional glyphosate-resistant weed populations have been identified: rigid ryegrass in a wheat production system in Australia and in California; Italian ryegrass in Chile; goosegrass in Malaysia; and horseweed (marestail) in the eastern, midwestern, and southeastern United States. The resistance mechanism in goosegrass is due to an altered target site, whereas the mechanism in the other weeds is under investigation.