People dig up and pull buffelgrass in Saguaro National Park in 2019.

 Courtesy of Frank Staub

Airborne and ground-based herbicide spraying and hand-pulling have shrunk what was once a 5-acre parcel of invasive buffelgrass in Saguaro National Park-West by 50 times over nine years.

On Saturday, a group of volunteers will spend up to four hours tackling the last tenth of an acre of the nonnative weed on a steep slope near Panther Peak at the park’s north end. Even for the extremely hardy buffelgrass, it’s an unusually stubborn patch, whose longevity is attributable to unique weather conditions there, among other factors.

It’s only one of seven buffelgrass removal efforts slated for a wide swath of Sonoran Desert landscapes over the next two weeks — a schedule that shows just how ubiquitous the weed has become.

The fast-growing perennial from Africa and Asia was first introduced to Arizona in the 1930s as hardy ground cover and forage for livestock. It has since exploded into a major threat to the desert ecosystem, by spreading even in dry years to crowd out native plants and fuel once-rare wildfires that are deadly to saguaros, paloverdes and other native plants. It now exists in every major public land preserve in the Tucson area.

Experts now consider it an existential threat to the desert ecosystem, on par with extended drought and climate change.

A deep yellow field of buffelgrass today adorns the remnant patch at Panther Peak, surrounding native saguaros and paloverdes, having filled in bare ground and pushed out other native plants, said Perry Grissom, a Saguaro National Park restoration ecologist.

“As a general rule in the park’s Tucson Mountain District, it takes three years to get (buffelgrass) under control. In that one it’s been different. We kept missing the seed” in past removal actions, Grissom said.

One reason that area’s buffelgrass is so hardy is that the soils are different from elsewhere in the park, he said. The slope there is also very steep, and “in the winter the sun is at a perfect angle to warm it up.”

“That’s why we get more germination than anywhere else. It seems like the weather is different there. It will rain there when it doesn’t rain anywhere else. It will skip there when it doesn’t skip anywhere else,” Grissom said.

At the same time, the buffelgrass’ roots are fairly shallow there, requiring volunteers to pull only two to three inches deep of the weeds, Grissom said.

The National Park Service paid an agricultural contractor to spray the area aerially with the herbicide glyphosate in 2014, 2015 and 2017. Manual removal started in 2018. Park Service staff has applied the herbicide on the ground and and volunteers have used tools to pull buffelgrass every year since then, he said.

“The seeds live for like five years in the soil. We’re killing the adults but the seedlings just erupt in the next monsoon,” Grissom said. “It’s so warm they’ve been germinating a lot in the spring. We keep missing them. In the past, I think, maybe once or twice, we sprayed in the winter. It would rain. We would go back, and then it’s too dry to spray.”

Digging up and pulling buffelgrass in Saguaro National Park in 2018.

Now, with such a small amount of buffelgrass left, “we’re getting kind of close to a knockout punch on this slope,” Grissom said, adding that he thinks it will take a couple years more to remove it all.

But even then, “it will take maintenance of the grass forever. There is buffelgrass seed still around. We hope to get it to the point where you only need a couple of people pulling them in the winter.”

Overall, “it’s here to stay,” he said.

The 45-minute hike to Saturday’s buffelgrass removal site is off-trail.

But if you volunteer, “not only will you spend time in one of the prettiest desert landscapes on earth, you may win a saguaro cactus for your yard,” organizers of the event say.

The Pima County Department of Natural Resources, Parks and Recreation donated a little saguaro in a one-gallon container that will be raffled off that day.

For more information, including driving directions to the area, contact trip leader Frank Staub at 520-260-1400, or fjstaub@hotmail.com.

Buffelgrass isn't the only weed causing trouble in Tucson. Video by Henry Brean/Arizona Daily Star

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Contact Tony Davis at 520-349-0350 or tdavis@tucson.com. Follow Davis on Twitter@tonydavis987.