By: Julianne Mason, Restoration Program Coordinator, Forest Preserve District of Will County
Five years ago, my coworker and I put in some test plots to compare the effectiveness of spraying reed canary grass with glyphosate, a non-selective herbicide, compared to treating it with clethodim, a grass-specific herbicide. Plots were treated in the late fall, early spring, or late spring in 2016-2018. The area is a remnant sedge meadow/ wet prairie in Joliet, Illinois. In the portion of the wetland that was sprayed in the late fall and early spring, reed canary grass had been scattered to moderately heavy, but native species were still present throughout.
Here’s my first article about those test plots: https://grasslandrestorationnetwork.org/2020/04/30/herbicide-treatments-to-reed-canary-grass-clethodim-vs-glyphosate/
When we put in the test plots, we marked treated individuals with pin flags. Since that time, we have not done any invasive species treatments there. The area was burned this past spring. After the burn, we were able to find many of the pin flags and evaluate the status of the treated reed canary grass plants five years later.
To my surprise, there is still a visible difference between the plots that had been treated with clethodim during the fall, compared to the glyphosate plots. Reed canary grass in the plots had been initially sprayed on October 21, 2016. In all plots, there is less reed canary grass now than there had been in 2016. However, there is noticeably less reed canary grass in the clethodim plots than in the ones treated with glyphosate.

In addition to having less reed canary grass in general in the clethodim plots, none of the marked locations from the 2016 treatment have alive reed canary grass now. However, in the glyphosate plots, more than half of the marked locations from the 2016 treatment have alive reed canary grass now.

This is interesting because roughly half of the clethodim-treated individuals had been recorded as alive but stunted in 2017 and 2019, while the other half had been recorded as dead. In contrast, nearly all of the glyphosate-treated individuals had been recorded as dead in 2017 and 2019. This suggests that the initial glyphosate treatment killed the reed canary grass. Since it is a non-selective herbicide, it also killed the sedges and other native species in the immediate vicinity, leaving visible “holes” in the vegetation. These holes probably provided space for reed canary grass to germinate and re-establish in the sprayed locations. In contrast, since clethodim is a grass-specific herbicide, it did not affect sedges and native forbs, and those plants were able to expand into the former reed canary grass locations.
The plots that were treated in the spring of 2017 were a different story. Roughly half of the marked locations where reed canary grass had been sprayed on April 21, 2017, have live reed canary grass now. There was not a noticeable difference between the two types of herbicide used.
Based on this case study, it seems that late fall treatment of reed canary grass with clethodim herbicide is quite effective! For the fall treatments, we used 0.75% Volunteer herbicide (clethodim product), with 1.5% Powerhouse which has ammonium sulfate (AMS) incorporated in the surfactant. Of course, reed canary grass has been re-invading into the plots, but I was completely surprised that the specific locations treated with clethodim herbicide have resisted re-invasion by reed canary grass over the span of the past five years!
This makes me double-down on my conclusion in the initial article: “In many of our natural areas, and especially immediately under invasive plants, the seed bank may not be our friend. It may have seeds of more invasive plants instead of native species. Creating ‘holes’ in the vegetation with non-selective chemical use can just make space for more invasive plant recruitment: spray and repeat, spray and repeat. To break out of that cycle, an end game is to facilitate renewed dominance of the native matrix, which seems to happen better and more quickly when a grass-specific herbicide is used to treat the reed canary grass.”
To my past self – yes, I totally agree! And now I add: late fall is a great time to spray reed canary grass with clethodim herbicide.








































