A computer model backed up with field work proved that the uninterrupted use of glyphosate alone (i.e., five applications per season per year) would result in glyphosate resistance within four years. The computer model is part of a project to study weed resistance. Syngenta collaborated on the project with university weed scientists Paul Nev., University of Warwick, England; and Ken Smith and Jason Norsworthy, both from the University of Arkansas.

While the project showed weed resistance developed, it also showed that diversifying herbicide modes of action and herbicide-tolerant traits play a role in breaking the resistance development cycle.

“With the computer model, we were able to run thousands of scenarios, and the results were surprising,” said Norsworthy. “We knew utilizing residuals and reducing the soil-seed bank were key pieces of the puzzle. What we didn’t know was that early-emerging weeds produce exponentially more seeds than those that emerge with crop competition. With more seeds, there is a much higher probability that one of those seeds could be a resistant mutant.”

The key takeaway is growers who practice “zero tolerance” or not allowing Palmer amaranth to emerge and set seed have been able to transform disaster fields into highly productive acres again.

Les Glasgow, head of Weed Management Strategies at Syngenta, noted, though highly competitive, Palmer amaranth can be controlled with proactive weed-resistance management and recommended a few key tips for success, including:

  • Plant into clean fields following tillage or use herbicides like Gramoxone to burndown weeds.
  • Apply a preplant or preemergence residual herbicide like Boundary or Prefix in soybean to prevent weed emergence.
  • Overlap an early postemergence residual herbicide like Flexstar GT 3.5 in soybean.
  • Remove weed escapes from fields before they seed set.

For more information about weed management, visit Syngenta’s www.resistancefighter.com.