The county has quietly resumed its plan to spray a controversial herbicide on 200+ acres of Boulder County open space — let’s mobilize to ensure this chemical doesn’t enter our soil and water.
Last winter, enough of us spoke up that the county paused its plan to continue spraying Rejuvra (indaziflam) across our open space. That pause is over. The county now intends to spray this November. We need to make it clear we’re still paying attention — and this is still not OK.
This isn’t about fighting one chemical in this one instance. This is a call for the County to listen to their constituents' values and offer more transparency into their decision-making process. They need to offer clear articulation on the rationale for using these chemicals over other alternatives. These herbicides will impact BoCo public lands for years to come and contain compounds classified as forever chemicals.
For those who want more context on this, we provide information below on the following:
Background Context on Indaziflam & It’s Use Locally
Particular Concerns about Indaziflam
What We’re Asking For Now
We need the commissions to know we are still paying attention — and spraying this highly concerning chemical on our land is still NOT OK.
The pause proved something important: when enough residents raised their voices, commissioners listened and changed course. That’s not nothing. It’s also not finished. Moving forward with a “modified plan” that now gives small buffers to the most delicate areas means the core decision — spray now, keep studying later — hasn’t actually changed.
We have a real, near-term opportunity to protect our land. Here’s what we’re asking you to do:
1. Stay informed & sign up for updates via this substack.
We’ll be sharing periodic updates as new developments unfold. Stay informed by signing up here →
2. Contact your County Commissioners.
A short, specific email or call goes a long way — especially right now, while the fall spraying plan is still active and not yet underway. You can use this email template as a starting point & email the Boulder County Board of County Commissioners directly at commissioners@bouldercounty.gov or call their office at 303-441-3500.
3. Join us on Sunday, October 4th at Yellow Barn Farm.
Learn more and RSVP here.
We’re not asking the county to ban all pesticides or ignore wildfire risk. We’re asking them to prove — with thorough publically shared data — that this strategy is necessary and the best option out of many they have considered.
We convinced them of the importance of this twice already and it worked. Let’s do it again: louder and clearer.
— Grounds for Action
Important Context on Indaziflam and It’s Use Locally
Background Context on Indaziflam in Boulder County
The first, experimental research on Indaziflam was done in Boulder County from 2014-2019. The research was preliminary research to understand the impacts this new type of herbicide would have on the wider ecology. Because indaziflam is a pre-emergent herbicide it kills seeds, not existing plants and is designed to bind to soil stronger than most other herbicides. So far research on indaziflam has failed to document the impact on the seed bank in the soil where it is sprayed and the impacts on the surrounding watershed.
Indaziflam was developed by Bayer CropScience, first registered for turf and ornamental use around 2010–2011. Researchers at Colorado State University began testing it on rangeland starting in 2014 to control invasive cheatgrass, and Boulder County Parks and Open Space (BCPOS) became a field-trial site in 2015 — years before the EPA granted full rangeland registration in 2020, at which point the product began being marketed under the name Rejuvra. A 2019 study evaluating winter annual grass control and native species establishment was co-authored by BCPOS's own weed resource specialist, directly tying county staff to the research. Boulder County commissioners approved and then paused an expanded spraying plan in late 2024 following public concern, before authorizing a modified version in 2026 that gives more buffer to sensitive wildlife habitat and water basins. It is being promoted as a wildfire-risk management and native-plant protection tool. We aren’t convinced it is either.
Why We’re Against Spraying Indaziflam in Boulder County
Indaziflam, sold under the brand name Rejuvra, is a pre-emergent herbicide the county plans to spray by drone across our open space this fall. It works by preventing cheatgrass (and other) seeds from germinating.
Some of our main concerns are:
Indaziflam is designed to persist in soil for years. Once it’s sprayed, it stays for at least 3 years. Other impacts, such as how it moves through bodies of water and affects native seeds, are not understood.
It’s already changing our soil, not just killing cheatgrass. Multi-year studies on our own open space land found that while cheatgrass dropped, soil microbial communities shifted, nitrate levels rose, and organic matter declined. We are still learning what those changes mean for the long-term health of this land.
There is some evidence showing that Indaziflam or Rejuvra contains PFAS or “forever chemicals”.
It is an established fact that Indaziflam contains a fluorinated carbon bond similar to those found in “forever chemicals.” U.S. regulators currently use a narrow definition that excludes it from PFAS classification; European and international regulators use a broader one that would likely include indaziflam, which is why it is banned across Europe. In early 2026, independent testing from the watchdog group PEER reported PFAS detections in Rejuvra formulations themselves. This question is not resolved, but should be well before it’s use is continued.
Boulder County’s ecology is already fragile, and we don’t know enough to trust this approach.
Cheatgrass is one of the main targets for this spray, but given the drought we are in cheatgrass growth is down. We want explicit data from the county on why they have chosen these sites to spray and their specific justification for using this approach versus others — something they have not shared with the public despite requests.
Sources and further reading:
PEER independent Indaziflam PFAS testing report (2026) ·
FACT SHEET: Problems with Indaziflam
“A Potential New Herbicide for Invasive Annual Grass Control on Rangeland” (2016) https://www.sciencedirect.com/science/article/abs/pii/S1550742415001517
“Effect of Indaziflam on Native Species in Natural Areas and Rangeland” (2019) https://www.cambridge.org/core/journals/invasive-plant-science-and-management/article/abs/effect-of-indaziflam-on-native-species-in-natural-areas-and-rangeland/3FD2EA4502D93E7EDF9C179B5EBADF2B