The University of Illinois has released news of a new type of herbicide resistance. Weed scientists have confirmed one population of waterhemp in the state is resistant to HPPD inhibiting herbicides. The HPPD products include Laudis, Impact and Callisto and some others as premixes. HPPD herbicides are often foliar applied and until now have successfully managed waterhemp weed populations common in Illinois and across much of the Midwest.
Extension Weed Scientist Aaron Hager says University of Illinois researchers began looking into the possibility of an HPPD resistant population of waterhemp during the 2009 growing season.
"This particular population is one that we've worked with both in greenhouse and actually in the field during the 2010 growing season," Hager said. "We were alerted to its existence late last year too late to do anything in the field, but we were able to get some seed collected and begin our investigation of it in the greenhouse last winter."
Hager says the population of waterhemp under scrutiny is not adequately controlled with labeled use rates of HPPD inhibiting herbicides.
HPPD inhibiting herbicides were first released in the very late 1990s. Balance is a name farmers will recognize as a soil applied HPPD inhibitor. The foliar herbicides, like Callisto, came later. So HPPD inhibiting herbicides have been around a bit more than a decade. It's a fairly short timeframe and according to Hager is important to note in relation to the Illinois field were the HPPD resistance has developed.
"The field that the population was identified from was actually in seed corn production for many years," Hager said. "For most of the years, at least recently, the field was treated multiple times with this particular line of chemistry, so the selection intensity to find resistance to HPPD inhibitors was very, very high in this instance."
The first announcement of herbicide resistance in Illinois waterhemp occurred in 1997 with ALS-inhibiting herbicides. Since then, triazines, PPO-inhibitors and glyphosate have been added to the list. Researchers at Illinois are exploring how the HPPD resistance develops and working on management recommendations for farmers.