A phalanx of government agencies say a new test program could bring a breakthrough in fighting off the invasive buffelgrass in rugged terrain.
But the plan to send a herbicide-spraying helicopter into Tucson Mountain Park has some county supervisors concerned about environmental risks to other plants and animals, including people living nearby.
Pima County Natural Resources Parks and Recreation Department, the U.S. Forest Service, the University of Arizona and the city of Tucson are working on the project to evaluate the helicopter application of various amounts of grass killer.
The Forest Service has used the helicopter method before on other invasive plants in other states. This project will help determine whether it will work on buffelgrass, whether it works in rugged Sonoran Desert terrain and what concentration of a grass-formulated type of Roundup can do the trick.
County Supervisors Sharon Bronson and Richard Elías raised concerns about the project's side effects as soon as they found out about it this week.
They're happy to rid the west-side county park of the invasive grass that crowds out native grasses and fuels wildfires, but they're nervous about the controls in place to protect plants, animals and people near the site.
Bronson said she wants to know how the herbicide will only target buffelgrass when it's being sprayed from a helicopter onto a large area with diverse plants, and how the county can be sure the chemicals won't drift outside the study area.
"Unless we have those assurances, I'm not comfortable proceeding," she said.
Though several agencies are working on the project, Bronson said she thinks the county could stop it since the county owns Tucson Mountain Park.
Roger Carpenter, an area resident, said he wonders how the spray could possibly affect only buffelgrass and not also kill native grasses.
He also asked how limited the spray distribution would be and how the helicopter's own rotors wouldn't spread the spray more widely than intended.
"Yes we want to get rid of buffelgrass, but can you control the spraying?" Bronson asked.
County Administrator Chuck Huckelberry said he was always comfortable with the project, but he asked Kerry Baldwin, county natural-resources-division manager, to further explain the processes to Bronson and Elías.
It's a well-researched scientific trial, not a random experiment, Huckelberry said.
The supervisors should have their answers next week, Baldwin said, and the spraying is scheduled to be done shortly after that.
The plan is to spray the herbicide, a grass-formulated type of Roundup, on 12 one-acre sites in Tucson Mountain Park near Kennedy Park. The sites will receive different amounts of the solution to study its effectiveness.
The helicopter will fly 30 to 40 feet high to drop the solution, which will be applied in large drops so it falls straight down, Baldwin said. It will not resemble the mist of chemicals associated with a crop-duster application, he said.
The department predicts no more than 1 foot of overspray or draft outside the study perimeter.
The helicopter won't deposit the herbicide if there's wind, which could disperse the spray beyond the target area, or if more than a 50 percent chance of rain is predicted for up to six hours, Baldwin said.
The department plans to send letters about the project to neighbors within 600 feet of the site, which may only be about five or 10 property owners, Baldwin said.
"What happened, more than anything else, is not all of the information had been passed along to the supervisors. We're in the process of providing more information," he said.
To protect against curious onlookers or impacts to the helicopter staging area or test plots, the department was not planning to issue a general announcement about the project, Baldwin said.
The specific type of Roundup targets grass, so it shouldn't have an effect on cacti, trees or shrubs, Baldwin said.
That's one of the reasons for the study, said Allen White, a regional pesticide specialist for the U.S. Forest Service.
"Working in this dry environment there's some information that we really need to know, including how we're going to be able to affect the buffelgrass without harming anything else. Particularly, with non-target species, it's a matter of seeing how they withstand the spray," he said.
Other plants weathering the anti-grass spray would be one measure of success.
Concerns about the chemical's effects on animals and people are minimal, the agencies say. The chemical used in the Roundup breaks down quickly, usually in about 10 hours. After that it's not a threat to any plants or animals, Baldwin said.
"As far as animal toxicity, it is practically nonexistent. It's a safe herbicide to work with," White said.
And though a grass killer can't distinguish between a native grass and an invasive species, in most heavily-infested areas the buffelgrass has already choked back native grasses, Baldwin said.
Tucson Mountain Park was selected because it has a large infestation of buffelgrass, Baldwin said.
"It's the most threatened as far as our Natural Resource parks today," Huckelberry said.
It also has varied terrain that is hard for crews to get to to dig up or spray individual plants. The sites are away from roads and trails, minimizing the potential of people entering the area during the study, and the 12 one-acre sites are near each other for easy comparison, Baldwin said.
The steep terrain is important in the study because if the aerial spray is successful, it could be used on buffelgrass in the Santa Catalina Mountains, Baldwin said. Previously, the Catalina peaks were separated from the populated Foothills by rocky expanses without plants.
"Now if we get a fire that started down along foothills, it can take it all the way to the flammable part" of the mountain, Baldwin said. "We have large stands of buffelgrass in remote mountain areas, the Catalinas, Tucson Mountain Park, Saguaro National Park. The cost of treating buffelgrass is expensive because of time spent hiking in and out and getting water in. This aerial technology is one that we think will give us a cost-effective tool."
DID YOU KNOW
Buffelgrass was introduced to the desert as a fast-growing cattle-food source. It spreads easily and often prevents the natural growth of native grasses. When it dries it becomes easily flammable, increasing safety concerns along roads and other natural fire barriers.