Buffelgrass, once dismissed as a demure roadside weed, now grows throughout Tucson, in homeless camps and wealthy ridgetop neighborhoods. In a survey published last year, Van Devender and his colleagues found buffelgrass growing on nearly every unpaved city roadside, median and vacant lot, and radiating deep into the deserts of southern Arizona.

"Buffelgrass is like taking a kiddie pool, filling it with gas, and putting it in your front yard," says Kevin Kincaid, a fire inspector for Rural/Metro, a private emergency services provider. "These fires can go from four-foot flames to 30-foot flames in 20 seconds." Kincaid used to assure Tucson homeowners that the desert was fire resistant. He now says buffelgrass has fueled between 15 and 20 fires in the city within the past six weeks, and he's telling residents to protect their homes by pulling and spraying as much grass as they can. "Otherwise," he says, "it's grab the cat and run for your life."

Colder winters have kept buffelgrass at bay in southern New Mexico, and low summer rainfall contains it in the California deserts. But buffelgrass shows no such restraint in Arizona. In Phoenix, 120 miles northwest of Tucson, the weed poses much the same sort of fire threats as in the Tucson Basin. It grows at elevations up to 5,300 feet in the Santa Catalina Mountains north of Tucson, raising fears that the increasing number of desert fires could jump into mountain forests. And on Tumamoc Hill, the research preserve on the western limits of Tucson, Julio Betancourt is watching a century-long tradition of botanical observation prepare to go up in flames.

Betancourt joined a growing number of converts to the anti-buffelgrass cause. By the early 2000s, corps of volunteers and paid staff, inspired by Sue Rutman at Organ Pipe Cactus National Monument, had long been straining their backs pulling and spraying buffelgrass in Organ Pipe, Saguaro National Park, and Tucson Mountain Park. Land managers throughout southern Arizona were already on the alert, and a handful of scientists had been studying the species for years. Even so, buffelgrass was spreading further and further each year.

"I realized that there was no point in doing this piecemeal," says Betancourt. "I thought, 'This isn't going to work until we have a framework in place - until we act collaboratively in a way that I haven't seen Tucson, or Arizona, do with anything else.' "

His work began with an accident. When a gas pipeline ruptured within city limits in 2003, Kinder Morgan set about repairing its network of 1950s-era lines, one of which crossed Tumamoc Hill. With environmental mitigation money from that project and the help of an environmental fund established by a nearby resort, Betancourt hired a young plant ecologist named Travis Bean to help coordinate a countywide buffelgrass campaign - an effort Rutman would dub "Julio's buffelgrass jihad."

Betancourt's was an unusual undertaking for a scientist, especially a government scientist. Researchers are expected to collect data, present it, and leave the political tussle to others, just as most of those on Tumamoc Hill had for a century. To do otherwise often risks the censure of supervisors and colleagues. But Betancourt felt he had enough seniority - and cause - to challenge this tradition.

"I can understand the premise of being objective and non-advocacy, but if we follow that model in cases like buffelgrass, we can actually experience the unhinging of an ecosystem," he says. "We're the only people really standing in its way, and it's up to scientists to make sure that people understand what's at stake."

Betancourt's buffelgrass horror stories - delivered in a Texas-tinged baritone - did the job. Both he and Bean gave dozens of talks, describing the spread and impacts of buffelgrass to county officials, state representatives, homeowner's associations and resort developers. They put aside scientific talk of interspecies competition in the desert and took up the cry they believed everyone could understand: Fire!

Variations on their story - weeds, fire, big trouble - now echo throughout Tucson. "People come to Tucson for the desert and the scenery, and it's going to be changing," says state Rep. Olivia Cajero Bedford, D, whose homeowner's association hosted a buffelgrass talk. "Julio has opened a lot of our collective eyes," says Pima County economic development and tourism director Tom Moulton, who adds a booster's flourish: "We're a lot prettier than some of the other cities that have had trouble with it, so we have a lot more to lose." Under its Sonoran Desert Conservation Plan, the county is buying open space to protect wildlife habitat - a project that buffelgrass could well render meaningless.

Betancourt and Bean succeeded in convincing the state to add buffelgrass to its list of noxious weeds, a move that prohibits the import of seeds and plants and opens funding opportunities for local governments. Their forceful proposal met with only minor opposition.

Even buffelgrass itself helped the cause. Heavy rains in 2006 fed the invasion, and the yellow hillside carpets became obvious even to untrained eyes. Last fall, about 400 people volunteered to spend a day pulling buffelgrass in Sabino Canyon, a popular hiking spot in the foothills of the Santa Catalina Mountains. This past spring, Betancourt and Bean helped draw more than 100 people, including many federal, state and local officials, to a buffelgrass summit co-sponsored by Pima County. They're now pushing fire departments to publicize buffelgrass-fueled fires - currently categorized as "brush fires" - and continuing their efforts to pull and spray hundreds of acres of buffelgrass on and around Tumamoc Hill itself.

"We've raised things to a frenetic level, and I'm not apologizing for that," says Betancourt. "I think it's necessary."