Wild poinsettia, or Euphorbia heterophylla, has been confirmed resistant to glyphosate in Brazil, making it the eleventh weed in the world to develop resistance to the herbicide. “We have about 50-70 acres of glyphosate-resistant wild poinsettia at this time,” says Ribas Vidal, weed scientist at the Federal University of Rio Grande do Sul (UFRGS) who confirmed the resistant population.
The population was found in a field in the main soybean growing region of Rio Grande do Sul, Brazil. “Farmers have been complaining about the need for higher rates of glyphosate to control wild poinsettia on a widespread scale for quite some time,” Vidal says. Biotypes from three additional sites are being tested and more areas of resistance are suspected.
When growers complained about lack of control and the need for higher rates of glyphosate, Vidal began investigating the possibility of resistance. “It isn’t surprising that wild poinsettia has developed glyphosate resistance because it’s historically prone to developing resistance. It’s the first Brazilian weed to develop multiple resistance to herbicides,” Vidal says.
Vidal recommends integrated weed management for control including rotating herbicide modes of action, reducing the seed bank population and rotating crops. “Wild poinsettia being identified resistant to glyphosate herbicides just demonstrates that no herbicide is a silver bullet. No technology is. Herbicides must be used wisely.”
“This is a very significant development for Brazilian farmers,” says Nestor Silva, regional development manager for Syngenta in Brazil. “Diversity in crop rotation and herbicide use are measures that we must implement to give sustainability to glyphosate herbicides and glyphosate technology.” Millions of acres are treated to control wild poinsettia. Heavy infestations can reduce yields by up to 40%.
“Farmers will have to include other herbicides to control this weed,” Silva notes, “starting with a pre-plant burndown – combining glyphosate in programs with other non-selective chemistries such as paraquat or 2,4-D. For over-the-top applications, the best alternative is PPO herbicides in combination with glyphosate. Preventing the weed from setting seed with the use of a pre-harvest aid is also advised.”
Globally, Syngenta advocates the responsible use of glyphosate in order to preserve the herbicide and help delay the onset of resistance. In U.S. glyphosate-tolerant corn and soybean programs, Syngenta recommends using no more than two applications of glyphosate in one field over two years – or 2-1-2. “Wild poinsettia resistance is another alert that glyphosate weed resistance is a real and growing threat not only in this country but in South America as well,” says Chuck Foresman, head of herbicide resistance management for Syngenta in the U.S. For more information visit resistancefighter.com.