Dr. Aaron Hager’s Perspective on Battling Herbicide-Resistant Weeds

September 14, 2022

“It’s the bottom of the ninth. The weeds have the bases loaded and there are no outs, and they are already up 15 to nothing. The weeds are clearly in the driver’s seat right now,” said Dr. Aaron Hager on the August 22, 2022, episode of the UPL podcast “The Root of the Matter.”

Dr. Hager, weed scientist at University of Illinois Extension for nearly 30 years, has studied herbicide resistance for most of his career. His research has uncovered many solutions to the issue, including using concentrated ingredients such as metribuzin. Although scientists have not solved herbicide resistance, Dr. Hager is still on the front lines working to discover new, much-needed strategies.

“We are learning more and more about the new resistance mechanism in these weeds,” Hager says. “In 1993, we had three species that had confirmed resistance in the state of Illinois, and now it’s about four times that number, with around 12 to 13.”

Amaranth is an especially invasive and resistant weed that plagues crops across the country. Dr. Hager explains that the way to beat these weeds is to inhibit their ability to make seeds during the growing season. PREVIEW 2.1 herbicide from UPL controls target weeds through pre-emergent and fall burndown applications, which eliminates the next generation of resistance by reducing resistant weed seed production.

“If we try to combine two, or perhaps even more than two effective herbicides together, then the probability of the weeds being able to overcome that very quickly is greatly reduced compared with, again, just a single herbicide active strategy,” Dr. Hager said. “What the data clearly showed is that exposing the population to more than one effective herbicide was a much better strategy.”

The unique 2:1 ratio of metribuzin and sulfentrazone in PREVIEW 2.1 is extremely beneficial for broadleaf weed control. The ingredient metribuzin has been demonstrated to be effective against resistant weeds. However, studies show that combining metribuzin with one or more additional effective ingredients can increase control, which is why PREVIEW 2.1 has been formulated with two effective concentrated active ingredients.

Dr. Hager also discussed other practices for combatting weeds that work effectively along with herbicide control.

• Cover crops serve many useful purposes in soil quality and structure, nutrient diversity and weed control.
• Crop rotation is a benefit in weed control. Switching from annual to perennial crops can disrupt the life cycle of the annual weed species, decreasing its ability to successfully reproduce.
• Manual weed removal is a labor-intensive effort but effective in preventing weed seed production.

Finally, the use of multiple control tactics has been proven to be the most effective in the control of any weed species. Combining effective herbicides, crop rotation, cover crops and different application methods can control weeds and combat resistance.

“It is based on biology,” Dr. Hager said. “It is very unlikely to be controlled by any one single tactic. So the more points in the growing season that we can introduce a major controller, the more likely we're going to have success by the end of the year.”

For more information, contact your local UPL representative. You can also listen to the entire podcast, below.