Year-Three Results – August 2025
By: Karen Glennemeier – Habitat Research LLC
and Jeff Weiss – Living Lands Conservation Company
Tall goldenrod (Solidago altissima) has become one of our most aggressive invasive species, especially in newly-opened woodlands and young prairie restorations in northeastern Illinois. While dense monocultures of this native species may have been present in patches across the historic landscape, most of us agree that we don’t currently have the luxury of allowing it to run its course within our small, fragmented natural areas.
We’re all trying various control methods and sharing our anecdotal successes and failures. This study set out to test a few of the more common methods systematically, to see what more we could learn.
We focused on seven different management methods commonly used (or newly of interest) in mesic to wet-mesic prairies. We would have liked to include more treatments and combinations of treatments, but we needed to keep the study manageable in scope!
We’re only three years into the study, so these results are very preliminary, but we thought we’d share what we’ve got so far.
The treatments consist of eight circular, 9 m2 plots. Within each plot, we have conducted each of the following treatments annually since 2023:
- Control
- Wood Betony – scattered approximately 500 stratified seeds of Pedicularis canadensis.
- Dodder – scattered approximately 25 seeds of Cuscuta glomerata.
- Both Wood Betony and Dodder, as described in #2 and #3 above.
- Mow without seeding – mowed all plants within the plot (brush cutter, scythe, or clipper).
- Mow with seeding – mowed as in #5 above and scattered 1.5 cups of cleaned seeds. Seeds were Citizens for Conservation’s prairie “power mix” (see species list below).
- Herbicide without seeding – spot treated tall goldrenrod with foliar application of selective herbicide (1% clopyralid).
- Herbicide with seeding – spot treated as described in #7 above and spread seeds as described in #6 above.
In our mowing treatements, we cut everything in the plot in order to mimic the typical mowing control of large goldenrod monocultures. In our herbicide plots, we only selectively herbicided tall goldenrod, again to mimic the way this treatment is typically employed (mostly in smaller sites). This difference means it may be harder to draw apples-to-apples conclusions about what’s behind the results, but ultimately what matters most is studying the methods that people are actually using in the field, so we’re ok with the trade off.
We are monitoring two responses to the treatments:
1. Tall goldenrod abundance
2. Overall floristic quality
To monitor the response to our treatments, we estimate percent cover of all species within four 1/42m quadrats within each test plot. We first took data in early August, 2023, and then we cut and herbicided the treatment plots the following week. In December of 2023, we spread seeds in the seeded plots.
We repeated this monitoring and treatment in 2024 and 2025. We have four replicates, doing all eight treatments at four different sites in Cook County, IL.
It’s very early, and we plan to continue the study for at least another five years, but here’s what we’re seeing so far:
(Error bars are standard errors of the mean. If they overlap, this roughly means the differences are not statistically significant between treatments.)
The main takeaway thus far seems to be that selective control plus supplemental seeding is the most effective strategy. If one wanted to avoid the drop in FQI with the herbicide-only treatment, which presumably is due to underground collatoral damage, one could try selectively cutting rather than selectively herbiciding, as some stewards do (typically using scythes).
Other thoughts:
1. We haven’t yet seen any betony germination, so it’s too early to know its impact, although the slow pace certainly suggests betony is not a quick solution to an emergency infestation. Anecdotal reports from other stewards suggest it may be a very effective long-term solution, though.
2. Dodder has not yet been recorded in all of its treatment plots, so, as with betony, we are still waiting to see its full impact. Anecdotal reports from other stewards suggest it is a very promising management tool, although germination of the seeds can be hit-or-miss, so this could limit its effectiveness until we figure this part out.
3. Oddly, cutting alone isn’t affecting FQI after two years. We’d have expected it to suppress FQI, since we’re cutting everything in the plot. We’re not sure what to make of this and are going to see how it plays out over time.
Thanks to Openlands for supporting this study and to the Forest Preserves of Cook County, ComEd, Citizens for Conservation, and the Village of Buffalo Grove for site access and research permission. Thanks for field assistance to: Luke Dahlberg, Adhya Garapati, Deepthi Garapati, Sue Gorr, Elizabeth Plonka, Karl Rosenberg, Ken Schaefer, Dana Sievertson, Anne Stake, and Agnes Wojnarski.
Seeded Species List
| Allium cernuum | Nodding Wild Onion |
| Anemone cylindrica | Thimbleweed |
| Asclepias syriaca | Common Milkweed |
| Asclepias verticillata | Whorled Milkweed |
| Bouteloua curtipendula | Side-Oats Gramma |
| Bromus kalmii | Prairie Brome |
| Cirsium discolor | Pasture thistle |
| Coreoposis palmata | Prairie Coreopsis |
| Elymus canadensis | Canada Wild Rye |
| Eryngium yuccifolium | Rattlesnake Master |
| Euthamia graminifolia | Grass-Leaved Goldenrod |
| Gaura biennis | Biennial Gaura |
| Helianthus pauciflorus | Prairie Sunflower |
| Heliopsis helianthoides | False Sunflower |
| Monarda fistulosa | Wild Bergamont |
| Oligoneuron rigidum | Stiff Goldenrod |
| Parthenium integrifolium | Wild Quinine |
| Ratibida pinnata | Yellow Coneflower |
| Roegneria trachycaula | Slender Wheat Grass |
| Rudbeckia hirta | Black-Eyed Susan |
| Schizachyrium scoparium | Little Bluestem |
| Silphium integrifolium | Rosin Weed |
| Silphium laciniatum | Compass Plant |
| Solidago juncea | Early Goldenrod |
| Sporobolus heterolepis | Prairie Dropseed |
| Symphyotrichum novae-angliae | New England Aster |
| Tradescantia ohiensis | Common Spiderwort |
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