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Chemical Companies get creative in engineering new herbicide solutions
−− By Josh Flint
Jul. 15, 2014
Super weeds have changed the farming landscape.
Previously, sites of action and modes of action were of utmost importance to understanding weed resistance to herbicides. Then, with funding provided by Syngenta, University of Illinois researchers identified something they had never seen before. In many instances, super weeds such as Palmer amaranth and waterhemp are overcoming the chemistry via increased herbicide metabolism.
"What we're seeing is resistant populations of these weeds are able to break down a herbicide into a non-toxic form much faster than sensitive plants," explains U of I weed scientist Aaron Hager.
When spraying HPPD inhibitors on resistant waterhemp plants, researchers identified the mechanism of resistance was something termed the P450 system. Put simply, waterhemp's P450 system breaks apart the HPPD inhibitor before it can kill the plant.
Now researchers are discovering even more ways weeds are thwarting ag's best chemistries. Take glyphosate sprayed on resistant populations of waterhemp and Palmer amaranth. Hager explains that somehow these resistant plants have been able to multiply the number of target sites within the plant.
"There are too many target sites that remain uninhibited in these plants to effectively shut them down," Hager notes.
Hager is quick to add that the numerous-target-site phenomenon is a plausible theory to explain some instances of resistance. In other instances, waterhemp plants without excessive target sites have also developed resistance to glyphosate.
New HPPD inhibitor
It's in this climate that Syngenta is releasing a new HPPD inhibitor, which should be available for the 2015 growing season.
The active ingredient is called bicyclopyrone. On the shelf, growers will identify it as Acuron, which will be sold as a premix with atrazine, S-metolachlor and mesotrione. Gordon Vail, technical product lead for Syngenta Corn Herbicides, says the resistance risk is too high to sell bicyclopyrone on its own.
"This chemical has been in development for several years now," Vail notes. "It's really designed for tough to control weeds like giant ragweed, morning glory, waterhemp and Palmer amaranth."
While Acuron will be sold as a pre-emergence herbicide, Vail says the label will allow for applications in corn up to 12-inches tall.
Potential long-term solutions
Vail agrees that U of I's research indicates a new mode of action or target site may not be the best course of action moving forward.
"Palmer amaranth formed resistance to three or four chemistries in quick succession," Vail notes. "Many of these are metabolic in nature. So, a new mode of action wouldn't necessarily help for long."
Instead, Syngenta is experimenting with different chemical structures. To date, most herbicides are weak acids, Vail says. Palmer amaranth and waterhemp have proven to be very good at breaking down these weak acids.
Not wanting to reveal too much, Vail says that Syngenta is working on something completely different. In house, they're calling them resistance buster molecules.
Other companies are also experimenting with new technology. Monsanto is pushing forward with RNAi technology, which silences certain genes in plants. If directed at those that metabolize herbicides or additional sites of action, Hager notes this technology could restore the usefulness of certain herbicides.
Hager also notes that he wagers some companies are working to add safeners to herbicides that were previously injurious to crops.
In the meantime, this discussion only highlights the need for growers to utilize effective resistance management techniques.
"This is not happening in some far away land," Hager adds. "Resistance is right here in the Midwest."
Source: Farm Progress
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