After the 2020 Calwood fire burned 22 homes and the 2021 Marshall fire destroyed 1,084, any government initiative towards reducing wildfire risk is welcomed. Unfortunately, herbicide spraying to control cheatgrass in our natural areas has not been documented to accomplish this. Nonetheless, the spraying campaigns now include fire mitigation as one justification.

Cheatgrass, also known as downy brome, is not a new species in Colorado’s open spaces. It has been widespread in the region since the early 1900s. It occupies newly bare ground and can provide the first vegetation after disturbance — from cattle grazing, fire, or the herbicide applications themselves.

Neither the Calwood nor Marshall fire was fueled by cheatgrass. The tall dry grass the Marshall fire traveled through was not mainly cheatgrass. Ditto for the Calwood: in the lower foothills, the fire burned through areas of cheatgrass and “restored” sprayed areas alike.

According to presentations by Boulder County Parks and Open Space staff, some of the Calwood burnt areas had been treated in 2018 by Bayer Esplanade (19% indaziflam). The treated areas still burned. Ironically, the focus of open space fire control has long included controlled burns to remove excess fuel, including tall perennial grass. Yet these same tall grasses are what indaziflam spraying of cheatgrass is designed to nurture.

There are other measures that can decrease fire hazard. Reducing fuel loads in the forests and shrublands is one approach; fire breaks are another, resistant building materials are another. Providing our public agencies, in the name of fire protection, with blank checks for helicopters to spray herbicides from the air to “treat the cheat” is not responsive to the need.

Doing the same thing over and over and expecting different results is not sensible. For decades, the chemical companies have  been selling the herbicide glyphosate and other synthetic herbicides to control cheatgrass in Colorado open space parcels. Thus, a recent Boulder County-sponsored study documents glyphosate, indaziflam, indazipic, quinclorac, aminopyralid, and mesulfuron methyl spraying histories in areas that were burnt in 2020.

Now the Bayer company is heavily marketing the pre-emergent herbicide Rejuvra: It contains the same 19% indaziflam active ingredient as Esplanade and was approved by the Trump EPA for aerial spraying. Unfortunately, while there are studies supported by the company in “partnership” with public employees that appear to demonstrate the utility of this approach, noticeably lacking are the independent analyses of efficacy for hazard reduction and also the needed evaluations of the ecological costs.

Two examples:

  • In April, 2022, a Boulder County Parks and Open Space staff member was a speaker at a Rejuvra herbicide webinar along with three Bayer employees. The Colorado Open Space Alliance, an organization of publicly funded open space programs, advertised the webinar, and described the product this way: “The Solution: Rejuvra Herbicide”. 
  •  At a 2021 Virtual Conference held by the Colorado Chapter of the Wildlife Society, county staff presented “successes” using Rejuvra, together with a Bayer employee as co-author. 

In this way, public employees are collaborating with company personnel to jointly advertise and endorse, by brand name, the extensive use of a patented herbicide. Then, their own land management agencies purchase the same product, which only this company sells. The Colorado public will not obtain impartial findings about weed control, public safety risks, or fire-protection efficacy in this way.

Meanwhile, there is secure knowledge that aerial spraying of our “priority conservation” and other open space land not only poisons next-year’s emergent cheatgrass, but most other annual plants. Recent studies elsewhere demonstrate profound negative effects. From the research literature:

Montana: “Indaziflam was highly effective at controlling the emergence of annual mustard… Unfortunately, the richness and diversity of the nontarget plant community was significantly impacted.”

Wyoming: “Shallow and deep native seed bank density and shallow native seed bank richness were significantly reduced in treatment plots.”


In Boulder County, the potential negative effects include rare annual species, which are especially vulnerable to aerial spraying campaigns such as recently conducted. Plants present in sprayed areas include “slimleaf milkweed, grassy-slope sedge, redstem springbeauty, stiff sunflower, wild lettuce, blue toadflax, venus’s looking-glass, bell’s twinpod (found only in Boulder and Larimer counties), deer pea vetch,” and others. This study notes: “Until proven otherwise, we expect that Esplanade will also control or suppress native annuals, biannuals, and perennials.”

Can we poison our way into ecological wildland restoration, and a fire-resilient future? It appears that unless thoughtful citizens and independent organizations scrutinize these plans, as well as the influence on public decision-making being exerted by major chemical companies; unless we insist that the usefulness of aerial spraying be validated by independent studies before it is used, our public lands will continue to be locked into a cycle that benefits only the sellers of the products. This is: spraying expensive chemicals to kill the cheatgrass and most other annual species, resulting in bare ground and a diminished  flora, then new cheatgrass growth, and then more spraying for “wildfire mitigation.” 

This cycle will continue unless the public and our elected representatives demand accountability and objective science.

Robert Brakenridge, of Lyons, is a senior research scientist at Institute of Arctic and Alpine Research at the University of Colorado.

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