Just when you thought buffelgrass was bad, here comes another non-native plant to threaten Tucson's desert ecosystem. Stinknet, also known as globe chamomile (Oncosiphon pilulifer) is an annual plant native to Africa. It has been spreading in California, Nevada and Arizona over the past several years, and recently forced the closure of Casa Grande Ruins National Monument which is still in effect.
Officials closed the park because stinknet spreads very easily on shoes and requires very aggressive control measures. Even a single plant can produce many thousands of seeds, and these seeds can survive in soil for years. This is why it’s critical to identify stinknet in your yard and neighborhood so that it can be removed. The best time to remove it is of course before it flowers and seeds.
So what’s the fuss? Not only does stinknet threaten our native ecosystem through aggressive spreading, it creates a fire hazard similar to buffelgrass. When dry, it is considered a flash fuel, which means that it will catch fire with a single small spark or a cigarette. It causes allergies and hypersensitivity reactions in people, as well, including asthma and nausea. And to top it off, it’s inedible to livestock, so it’s a real threat to our rangelands as it replaces native, edible plants. For all of these reasons, stinknet was listed in 2020 as a noxious weed by the Arizona Department of Agriculture.
Identifying stinknet
The best measure is prevention, and for that you need to be able to find and correctly identify stinknet. It is a cool-season annual and can grow up to 2 feet in height and about the same in width. It germinates in November or December, and begins to flower around February, and is particularly likely to grow during a wet winter.
The flowers are about the size of a pencil eraser, bright yellow, and globe-shaped. Each globe contains many flowers, and each of these flowers can turn into a seed. Thus each plant forms thousands of seeds when mature. When it’s flowering, stinknet can’t be confused with any native plant, as nothing else looks like it in the natural landscape.
The best strategy is to remove the plant before it flowers, so identification of the leaves is critical. They look like the foliage on carrots and are dark green. The key is the smell, which is a pungent, turpentine-like odor released when you rub or crush the leaves (with gloves on!), which gives the plant its name. The odor is described by some as pleasant and by others as nauseating. It can cause headaches and even trigger asthma, so don’t inhale a big whiff — just waft the odor towards your nose to identify. Again, be on the lookout for it in early winter, when it’s most likely to germinate.
In April and May, with the onset of dry weather, stinknet begins to die, and this is when the seedheads dry out and spread thousands of seeds. The plant turns a golden brown. The seedheads are very fragile, so it’s difficult to remove the plant at this point without spreading seeds everywhere.
Here are some helpful resources for identifying stinknet.
Controlling stinknet
If you find stinknet on your property, you can use the following measures for controlling it, as recommended by the University of Arizona and Tucson Audubon Society:
- Ideally, do not let it flower. Eliminate it as soon as possible after it emerges so that the seeds don’t develop. Learn how to identify the leaves with the help of the informative websites listed below.
- Pull by hand or use a stirrup hoe or a weed wacker. Always wear protective clothing, including a face mask, when doing this due to the aforementioned allergic reactions. Clean the clothing thoroughly afterwards to prevent health issues and to destroy seeds. Tucson Audubon recommends having a special set of gloves just for removing stinknet.
- Remove stinknet carefully if it has flowered, particularly when the flowers are dried and the plant is dead – it will shed thousands of seeds, which can live in soil up to five years. You will need to bag it up in a sealed bag and throw it in the trash.
- You can use herbicides, including glyphosate and preemergent herbicides, to kill it. Always follow label instructions and wear protective equipment. Don’t try to wing it; only use a product manufactured and labeled for use as an herbicide. Note, however, that Tucson Audubon recommends hiring a professional for this, and can help you come up with a treatment plan through their invasive plant treatment program.
To help control stinknet in public areas:
- When hiking, always brush off clothing and shoes at the trailhead before and after your hike.
- Be sure to clean tarps, tents and other gear after camping. If you see stinknet on public lands, report it to stinknet.org or via email at InvasivePlant@TucsonAudubon.org.
- Do not allow pets to run through patches of dry stinknet as they will spread it everywhere. They may also suffer allergic reactions from the plant and it may be toxic to dogs. You will want to brush and likely bathe your pet if he or she is exposed.
- Be sure to look each year, particularly during wet winters, in your yard and neighborhood for young plants and remove them before they can go to seed. November through January is a great time to look as it should be before the flowers emerge.
The University of Arizona mentions that stinknet has been seen at farmer’s markets being sold as “wild chamomile.” If you see this plant being sold for human consumption, report it to stinknet.org.
Where to report stinknet in the Tucson area
If you find stinknet on public or private lands, the best place to report it is stinknet.org. This site, established by Tucson Audubon Society, allows you to report any infestation you see on their form. You will need an address or other location information. Try to estimate the size, number of plants, and include photos if you can. If you know the landowner information, you can put that in, as well.
You can also report stinknet on the citizen-science app iNaturalist at inaturalist.org.
For more information on identifying and treating stinknet:
- “Stinknet: a Weed Advancing In Southern Arizona” has a great overview of the plant and its threats, as well as lots of photos for ID purposes.
- Tucson Audubon Society’s site stinknet.org has a section on identifying the plant, as well as lots of other helpful resources. It’s also where you go to report sightings of the plant.
- Arizona-Sonora Desert Museum has a very helpful website on stinknet with pictures and other resources.
- Pima County Extension’s site on “Stinknet Invasion” is helpful, as well, with lots of information on the plant and how to control spread.
Where to volunteer for stinknet removal in the Tucson area
The noxious plant is running wild on a dirt lot near Stone Avenue and Prince Road.
