Researchers have concluded that common ragweed in a single field in central Missouri is resistant to glyphosate, the active ingredient in Roundup herbicides.
Preliminary results demonstrate resistant plants in a 20-acre section of the field can survive applications up to 10-fold that of a susceptible population.
Dr. Reid Smeda, a University of Missouri weed scientist, says there have been no other complaints locally and glyphosate is able to control common ragweed in other parts of the state.
Common ragweed is only the third weed biotype in the United States to develop resistance to glyphosate in nearly 30 years of commercial use. In addition to common ragweed, some biotypes of marestail and ryegrass also have shown isolated resistance. These cases have been effectively managed with tank mixes.
Monsanto and Smeda have worked together to develop a practical recommendation for this grower. Research has shown FlexStar or Phoenix herbicides can be tank mixed with Roundup agricultural herbicides for post-emergence applications in soybean. Valor or Scepter can be added to a soil-applied program. In corn, popular herbicides such as triazines and growth regulators can be added to an integrated herbicide program.
"Itâ€™s important that growers use the right rate of glyphosate for the right size weed at the right time, as well as additional weed control tools that may be necessary for the weed spectrum on their farm," reminds Doug Rushing, Monsanto's director of technology development. The vast majority of weed performance inquiries are due to improper application or environmental conditions."