Syngenta collaboration with university weed scientists has once again proved invaluable in the fight against weed resistance. In an effort to help growers overcome a rapidly spreading population of herbicide-resistant weeds, Syngenta and university weed scientists Paul Neve, Ph.D., from the University of Warwick in England, and Ken Smith, Ph.D., and Jason Norsworthy, Ph.D., both from the University of Arkansas, developed a computer model to explore the impact of various management practices on the evolution of glyphosate-resistant Palmer amaranth.

The model predicted and field work confirmed that, in a worst case scenario, uninterrupted use of glyphosate alone (i.e., five applications per season per year) would result in glyphosate resistance within four years. It also showed that diversifying herbicide modes of action and herbicide-tolerant traits play a critical 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.

“We invest in developing Resistance Fighter brand herbicides and supporting research like this because in the long term, we want to protect the tools we have and help growers succeed,” said Les Glasgow, Ph.D., head of Weed Management Strategies at Syngenta.

Glasgow 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 Gramoxone brand herbicides to burndown weeds.
  • Apply a preplant or pre-emergence residual herbicide like Reflex in cotton, or Boundary or Prefix in soybean to prevent weed emergence.
  • Overlap an early post-emergence residual herbicide like Dual Magnum or Sequence in cotton, or Flexstar GT 3.5 in soybean.
  • Remove weed escapes from fields before they seed set.