Update on herbicide resistance in waterhemp
“Keep in mind that these fields -- and plants within fields -- were not randomly selected but were sampled based on suspected resistance to glyphosate,” said Hager. He also noted that the field-level results are based on small samples (five or fewer plants per field). “It is likely that, had a larger number of samples been taken, we would have found more fields with resistance to ALS and PPO inhibitors,” he said.
Even with this sample-size limitation, over 10 percent of the fields were found to contain three different types of herbicide resistance, which greatly increases the difficulty of managing these populations using only postemergence herbicides labeled for use in conventional or glyphosate-resistant soybean varieties. Results from this and previous surveys suggest that glyphosate-resistant waterhemp occurs in many fields across the southern two-thirds of Illinois.
This survey was only one project in the ongoing research portfolio on herbicide-resistant weeds in Illinois. Weed scientists at several Illinois universities are studying this phenomenon and working to develop viable solutions for Illinois farmers. Much of this research is made possible by multiple public and private funding sources, including the Illinois Soybean Association.