Herbidcide resistance in weeds isn’t going away, but researchers are still looking for ways to slow down the phenomenon. With new research, Vipan Kumar, associate professor of weed science at Cornell, documented a synergistic effect for greater control of kochia resistant to multiple herbicide classes.
“There aren’t many new herbicide modes of action coming into the market,” he says. “We need to rethink weed control strategies and plans, especially for herbicide-resistant biotypes, differently.”
Kochia populations resistant to up to five different herbicide sites of action (groups 2, 4, 5, 9 and 14) have expanded to cause a weed management challenge for growers in the Great Plains and Midwest states.
With assistance from Belchim USA, Kumar oversaw studies when he was previously at Kansas State University that paired pyridate (group 6) with atrazine (5), glyphosate (9), dicamba (4) or fluroxypyr (4).
Adding pyridate (Tough 5EC) to the tank mix had a synergistic interaction for greater control of kochia with mulitple resistance to glyphosate, atrazine and dicamba.
Compared with separate applications of glyphosate or atrazine, resistant kochia control was increased from 26% to 90% with the application of glyphosate plus pyridate (Tough) and 28% to 95% with atrazine plus pyridate.
“We are getting limited on post-applied herbicide options for kochia control. This idea of synergy brings something new. It could be a solution for some of the resistant biotypes by adding a different site of action,” Kumar says. “This can play an important component of integrated weed management.”
Kumar’s research shows Tough truly synergizes other classes of herbicides (groups 5, 6, 9 and 4) along with the HPPDs (Group 27).
Dennis Long, national technical service and development manager at Belchim USA, says, “Years ago, we discovered the low use rate, synergistic impact of Tough on the HPPD herbicides. This is well-documented and is why we invested millions toward re-registration.”
Long says adding Tough to the tank costs $10 to $12 per acre. Tough is labeled for field corn, seed corn, popcorn, chickpeas, lentils and mint.
He describes how Tough acts like a Trojan horse. He says it is chemically engineered as a proherbicide to penetrate the leaf. Once inside the plant, it is broken down into the herbicidally active molecule and “carries in” other chemistries faster.
“There’s economic value in resistance management in achieving a higher level of weed control as well as reducing the number of seeds going into the seed bank. Especially with weed escapes, you’ve selected for the ones that are resistant, so we have to head that off,” Long says.
Kumar sees future research to include different synergistic use rates of pyridate for Palmer amaranth, horseweed and waterhemp.
“These are unexplored mechanisms for weed control. We need to understand the biochemical interactions of the molecules at the plant level and cellular level,” he says.
Read the full published research as it appears in the latest issue of Weed Technology Journal.
