Herbicide resistance continues to be a pressing issue for no-tillers.

As of early June 2021, the International Herbicide-Resistant Weed Database reported that there were 522 unique cases of weed resistance globally. A unique case means a specific weed species resistant to a specific site of action.

While that number is concerning, Iowa State University Extension weed specialist Bob Hartzler is more worried about the fact that there are a few weed species that are very efficient at accumulating multiple resistances. 

At the 2021 National No-Tillage Conference, Hartzler spoke on the biggest challenges of herbicide resistance, and why focusing on the weed seedbank will likely be key to keeping troublesome weeds under control.

Waterhemp, Marestail a Growing Concern

Hartzler shared data that shows just how many weeds are becoming resistant to more than one herbicide group, also known as the site of action. Nearly 60 weed species are resistant to at least two herbicide groups, 20 species are resistant to three groups, and just over a dozen are resistant to four. But there is already one weed — waterhemp — that is resistant to seven different herbicide groups.

“When we start accumulating this many resistances, that basically means we’re running out of herbicide options to control those weeds,” Hartzler says.

It’s not surprising then that in a…