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Johnnie St. Vrain: What Was the Helicopter Spraying at Rabbit Mountain Open Space?

March 24, 2019
Kevin Dean, of Longmont, begins a ride at Rabbit Mountain Open Space on Friday.

Dear Johnnie: We drove out to Rabbit Mountain Wednesday morning for a hike at one of our favorite open space areas. The gate was closed and locked and a helicopter was flying back and forth close to the ground spraying a chemical. I have never seen this at any of the open space locations. I am wondering what chemical was being sprayed and what it is being used for? Will this be happening again at other open space land?

A Curious Hiker

Dear Curious: Sorry you missed out on continuing your journey in the hills northwest of Longmont. What stopped you was a closure by the Boulder County Parks and Open Space Department to apply an herbicide to get rid of cheatgrass.

That is an invasive winter annual grass, a weed that has covered millions of acres across the American west in recent years and “has become a very big problem,” according to Boulder County Weed Coordinator Steve Sauer.

The helicopter was spraying Esplanade, a herbicide that takes care of cheatgrass and one of 13 that the county uses for various types of weed management on open space.

“In working with product for the last four years we have found that it controls cheatgrass over an extended period of time as compared to other herbicides which have to be applied annually,” Sauer said.

It was the first time a helicopter had been used to apply the cheatgrass-killing herbicide at Rabbit Mountain, Sauer said. Only rarely do county workers use a helicopter to apply herbicide to open space. They usually do so by tractor, utility terrain vehicle or backpack sprayers, which are for spot-spraying.

The county announces closures for herbicide spraying at Ron Stewart Preserve at Rabbit Mountain at the property’s web page at bouldercounty.org/open-space/parks-and-trails/ron-stewart-preserve-rabbit-mountain .

“By controlling this weed we allow other native grass to thrive and forbs to grow without competition from non-native grass species,” Sauer said.

Forbs are herbaceous, flowering plants other than grasses, and wildlife that graze in the area prefer forbs to cheatgrass, he told me. There are no grazing restrictions for animals in place since the herbicide application.

“By increasing the forbs we have found that we have increased pollinator habitat on other properties that we have made this treatment,” Sauer said. “We have also found that it increases shrub growth, which the wildlife in the areas feed on in the winter. Another benefit is that this herbicide breaks down the heavy thatch layer left by cheatgrass which adds to the wildfire danger we have seen in many areas of the west.”

You might see other herbicide applications done for nine of the 10 “List A” weed species that the state requires Boulder County to eradicate, the county’s weed management web page says. It also treats county property for 13 “List B” species — and you can read the county’s Noxious Weed Management plan to find out more about what species those are.

You can also call 303-441-3940 for daily updates on herbicide applications to county roads east of U.S. 36.

“We also use other methods for weed control which include mechanical, cultural and bio-control,” Sauer said.

I hope you can find the time to make it back to Ron Stewart Preserve at Rabbit Mountain — the Little Thompson Overlook trail is the shortest hike there at 1.5 miles but a little bit more difficult with greater elevation gain than the 2.2 mile Indian Mesa Trail.

Sam Lounsberry: 303-473-1322, slounsberry@prairiemountainmedia.com and twitter.com/samlounz .