We’ve all heard about bacteria that are becoming resistant to multiple types of antibiotics. These are the so-called superbugs perplexing and panicking medical science. The plant
In a new study from the University of Illinois, scientists document
There are many herbicides on the market, but they all fall into one of 16 classes describing their mode of action (MOA), or specific target in the plant that the chemical attacks. Because of various regulations and biological realities,
“In some areas, we’re one or two MOAs away from completely losing chemical control of
Illinois weed scientist and co-author Aaron Hager adds, “We don’t want to panic people, but farmers need to be aware this is real. It continues on with the challenges we’ve warned people about for years.”
The research team tested the effectiveness of soil-applied Group 15 herbicides in a Champaign County population already resistant to five MOAs. They applied eight Group 15 formulations in the field at their label
The eight Group 15 products varied in their effectiveness, with encapsulated acetochlor (Warrant), S-metolachlor, metolachlor (Stalwart), and dimethenamid-P (Outlook) performing the worst. These products provided less than 25% control 28 days after application and less than 6% control 14 days later.
Of the rate-titration experiment, Hager says, “We found we could apply significantly higher than the labeled dose and still see resistance.” For example, S-metolachlor provided only 10% control at the standard label rate, 20% at 2x the label rate, and 45% at 4x the label rate.
Hager says farmers might not notice the poor performance of these soil-applied pre-emergence herbicides because
“If you think about how you use these products, rarely do they last the entire year. They’re very dependent on environmental conditions to work effectively. It could be too wet or too dry. Generally speaking, you have some weed escape. But many farmers would chalk it up to these weather issues. If you’re not thinking about it, you could very easily overlook resistance,” Hager says.
To confirm results from the field, the team performed a
Hager suspects the plants are breaking the chemicals down before they cause damage, a trick known as metabolic resistance. All organisms can turn on cellular defenses against toxins, but it is rather worrisome when weeds and other undesirable pests use their biology against human interventions.
“As we get into the era of metabolic resistance, our predictability is virtually zero. We have no idea what these populations are resistant to until we get them under controlled conditions,” Hager says. “It’s just another example of how we need a more integrated system, rather than relying on chemistry only. We can still use the chemistry, but have to do something in addition.
“We want farmers to understand that we have to rethink how we manage waterhemp long term.”
The article, “Characterization of multiple herbicide-resistant
