The buckets of moisture heaped on the West this winter have solved some problems while watering others. Billions of canary-yellow orbs now drape southern Arizona’s desert like a fungal carpet. Vast fields of stinknet, an invasive shin-high herb also known as globe chamomile, emerged in early spring, out-competing native plants with startling efficiency. And when these swaths of yellow dry out and turn brown this summer, they will become fuel for wildfires that, as botanists have discovered, only end up expanding their range. It’s a weed that helps create the void it fills.
Stinknet, which is native to South Africa, derives its name from the odor emitted by its resinous blooms. The invasive plant was first identified in Southern California in 1981, but those early populations grew slowly compared to those that sprang up near Phoenix a decade later. “Maricopa County is heavily infested now. Stinknet’s coming up through cracks in the sidewalk and now working its way down the I-10 corridor,” said Michael Chamberland, a botanist at the University of Arizona who studied the plant to better understand what the state is up against. He said researchers are now finding the noxious weed in Northern Mexico and Las Vegas. Stinknet is also becoming well established in Tucson, Arizona, though early detection there means conservation efforts still have a fighting chance, at least compared to Phoenix.
Even for an invasive species, stinknet is formidable. Chamberland outlined the myriad ways it threatens the fragile Sonoran biome and complicates management efforts. The seeds are numerous — and tiny — while the plants themselves create vast “drifts that can cover entire landscapes and choke native plants.” Once desiccated, these drifts connect otherwise fragmented archipelagos of native cactus, shrubs and trees into a continuous pyro-corridor that other plants are not adapted to survive. People also struggle with the plant: Stinknet can cause rashes if handled without gloves, and, when it burns, produces an acrid smoke that irritates the lungs.
“Drifts that can cover entire landscapes and choke native plants.”
“Nobody knows” how it got to Arizona from the distant colonies in California, Chamberland said, nor how it arrived in the U.S. in the first place. During a phone interview in early May, Chamberland recounted Stinknet’s spread in forensic detail, like an epidemiologist hunting for patient zero. Scouring the Arizona State University herbarium, Chamberland turned up a clue: the first documented specimen in Arizona, dated to 1997, laminated on archival paper. The same botanist wrote a follow-up article in 2005, too. The article included a warning: “The author predicted back then that we need to be careful with this plant.” But that warning went unheeded in Arizona for almost 15 years.
A few years ago, a wave of winter storms pummeled southern Arizona, not unlike this year, and Maricopa County became infested with stinknet. Prompted by complaints from residents, the Maricopa County Parks and Recreation Department partnered with the Arizona Conservation Alliance to hold the line. “We started the Desert Defenders program in 2018,” said Juanita Armstrong, a natural resources specialist for the local parks service. They began hosting events to educate the public, deputized volunteers to pull out invasive plants, and developed a crowd-sourced surveillance system, where citizens can use their cellphones to report sightings on a real-time map. “We removed 1.5 million plants at 21 events in seven state parks this year,” Armstrong said; 92% of those invasives were stinknet. The Desert Defenders collect native seeds at the same time. The idea is to create “seed bombs” — chunks of soil filled with those seeds — and toss them into areas denuded by the cleanup operations.
“We removed 1.5 million plants at 21 events in seven state parks this year.”
Chamberland and Armstrong see these efforts as a step in the right direction. Still, for the time being, it’s a Sisyphean one: “The best way to deal with invasive species is EDRR: Early detection, rapid response,” said Chamberland. “Unfortunately, Arizona doesn’t have a statewide EDRR program. We’re behind some of our neighbors like Utah and California in that respect.” Tucson, with help from the Audubon Society, found success deploying “strike teams” that prevent the yellow drifts from becoming runaway tsunamis. Armstrong, however, said that Maricopa County will need to resort to herbicides, which may pose their own risks. “I don’t believe that we’ll be able to remove stinknet just by pulling it. We’re going to need some chemical methods as well.”
Zach Duncan is a creative from Cave Creek, Arizona.
Samuel Shaw is an editorial intern for High Country News based in the Colorado Front Range. Email him at samuel.shaw@hcn.org or submit a letter to the editor. See our letters to the editor policy. Follow Samuel on Instagram @youngandforgettable.
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