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INVASIVE SPECIES ALERT: Stinknet

An Eradication Priority species of the Sonoran Desert Cooperative Weed Management Area (SD-CWMA)

By Kim Franklin, Conservation Science Manager, Arizona-Sonora Desert Museum

By the time you read this, dense stands of bright green stinknet, with its striking yellow flowers, will have turned a drab brown. Stinknet (Oncosiphon piluliferum), also called globe chamomile and manzanilla apestosa, is a winter-spring annual native to South Africa, but highly invasive in the Southwest. It was first noticed in Phoenix in 1997, and in Tucson in 2015.

Stinknet has a pungent odor that most people find offensive. Inhalation of the volatile chemicals released upon burning has been implicated in cases of respiratory distress. There are other reports of contact dermatitis from skin exposure to stinknet.

In addition to its potential negative impacts on human health, stinknet presents a grave ecological threat. Nothing eats stinknet, not cattle, and or even goats! Although it appears to have some trouble competing with native vegetation, stinknet rapidly fills in open areas, in urban, agricultural, and wildland landscapes. These are areas in which native annual wildflowers might otherwise bloom. Late in the spring, tinder dry stands of stinknet connect distantly spaced patches of native vegetation, providing fuel continuity, spreading fire faster and farther in a desert that was not meant to burn.

Stinknet proliferates along roadsides, and when drivers pull off the road into patches of seed-laden stinknet, their vehicles break apart seed heads, freeing the tiny seeds to blow in the wind of passing traffic or hitch a ride on trucks or boots to new residential and industrial locations.

One of the most impactful ways that you can help is by simply NOT contributing to the spread. Clean trucks, equipment and clothing when you know, or suspect, that you’ve driven through or worked in an infested area. Dewalt makes a portable power washer that uses the same battery as many common landscaping tools, and just a few gallons of water is all that is required to spray down trucks, including the undercarriage. If you’ve been working in an infested area, it’s also important to clean boots and wipe down pants. Anything you can do to prevent spreading the seed from one site to another is a huge help!

Lastly, to report stinknet, please submit your observation at https://www.stinknet.org/ or email Tony Figueroa of Tucson Audubon Society, which is actively working to control stinknet in the Tucson Basin. tfigueroa@tucsonaudubon.org

*Photo courtesy of John Scheuring*