Stinknet Has Reached Dewey-Humboldt, Arizona

Yesterday (June 14, 2019), I discovered a new invasive weed growing in Humboldt. The plant’s small yellow flowers caught my attention as I walked along Old Black Canyon Highway. Roads are common dispersal routes for invading weeds. First the roadsides, next the yards and hillsides.

Stinknet (Oncosiphon piluliferum), an invasive desert weed.

The first thought produced by Stinknet is that its bright yellow flowers are beautiful. The next thought, however, is that something stinks. Stinknet produces resinous sap that smells like a rotten pineapple. The odor plus the tendency for the plants to grow in tight formation create real impediments to outdoor activity. Even worse, Stinknet is a strong competitor that replaces native plants. But worse still, the plants are highly flammable and encourage destructive wildfires. If Stinknet invades, the quality of natural habitats will decline and many soil organisms, native plants, and native animals will disappear.

Stinknet is spreading across the hot deserts of California and Arizona. I’ve known about the weed since 2008 when Andrew Salywon of the Phoenix Botanical Garden ranked it as one of four weeds posing the greatest threats to Agua Fria National Monument 20mi south of Humboldt. The plant has not been reported above 2300ft in Arizona, and I assumed that at 4500ft, Lonesome Valley winters would be too cold for Stinknet. I did not even include it in the list of possible future weeds in Weeds of Dewey-Humboldt, Arizona. Let’s hope that other dangerous weeds that I did not list will not reach Lonesome Valley.

Stinknet is a member of the Sunflower family. It’s small round yellow flower heads are composed of 100 to 250 flowers packed into a ball no more than 1cm (1/2in) in diameter (Copyright 2019, Garry Rogers).

Treatment: How to Control Stinknet

Though people have carried Stinknet thousands of miles from its South African home, and though the plant has dispersed rapidly along Arizona highways, Stinknet may not survive and spread in Dewey-Humboldt. However, that’s not a safe bet. Like medical doctors, weed professionals practice EDRR (Early Detection Rapid Response). Now’s the time to begin watching for the plant along the highway and town streets. At this early point in Stinknet’s invasion of Dewey-Humboldt, the best control tactic is pulling and bagging the complete plant including the roots. If the plant spreads, control will become much more difficult and expensive. Like any disease, weed invasions are easier to cure when discovered early.

Stinknet (Copyright Max Licher).

Identification

Stinknet (Oncosiphon piluliferum) Daisy Family—ASTERACEAE.
Annual with persistent roots. Small, less than 2ft tall. One to five or more thin stems arising from base, sparse alternate leaves, striking yellow flowers in small tight balls less than 10mm diameter. Stinky.

Illustrations of the Weeds of Coldwater Farm

All invasive plants are weeds but not all weeds are invasive.

In fact, a great majority of weeds aren’t invasive. Most are native plants that respond to natural and human-made disasters by covering and protecting exposed soil. They do not invade native vegetation by spreading among the longer-lived, shade-casting plants that make up what we call climax vegetation. Here are illustrations of the 153 weed species observed or expected to appear at Coldwater Farm. Click images to see weed names and image creators. If there is no name or creator given, or if you want information on a weed’s characteristics including its value as medicine and food, refer to the book Weeds of Dewey-Humboldt, Arizona available from Amazon.

Drawings, Paintings, and Photographs

Plant identification is easier with drawings made by an experienced botanical illustrator than with photographs. In photographs, important features aren’t always distinct on a particular leaf or flower. An illustrator can emphasize the appropriate features. Photographs are useful for showing plant colors and typical settings with other plants.

For each weed, I tried to present the best illustrations available. Many of the drawings are by Lucretia Breazeale Hamilton from the book An Illustrated Guide to Arizona Weeds by Kittie Parker published in 1972. In the gallery, they are usually identified as “Parker”. They are included with the generous permission of the University of Arizona Press. Most of the photographs have Creative-Commons licenses that allow reproduction only requiring attribution to the photographer (CC BY 2-4 and BY-SA 2-4). I did not alter the photographs except as needed to fit them on the page and make them suitable for printing. Some of the drawings and photographs are from U. S. government web sites and are in the public domain. Paintings were available for some of the weeds. The ones I used are over 100 years old and are in the public domain. For all images, Weeds of Dewey-Humboldt, Arizona has the names of creators in the captions and in an Index of Illustrators, Painters, and Photographers just before the General Index.

You can find more works by the photographers by entering their names or the names of the plants they depicted in the search box at Wikimedia Commons, Wikipedia, or Flickr Creative Commons. “GR” in a caption identifies photos by me. You can use my photos as long as you attribute them as “© Garry Rogers.” Look up Creative Commons BY-SA 4.0 to read the license requirements.