Stinknet (Oncosiphon piluliferum), also called globe chamomile, is an invasive winter annual spreading across parts of the southwestern United States and northern Mexico. Dense patches can crowd out native plants, and dry standing growth can carry fire through otherwise sparse desert vegetation. Some people also report skin or respiratory reactions, although regional sources say the health effects need further study.
If you find it, identify it carefully, control it before it disperses seed where practical, clean anything that may carry seeds away, and check the area again: new plants can emerge in later cohorts.
How do you identify stinknet?
Look for a combination of features rather than relying on one clue. Stinknet has dark green, finely divided, carrot-like leaves, a pungent odor, and small, bright yellow, spherical flower heads. It is a cool-season winter annual; Arizona classifies it as a Class B noxious weed. Arizona Invasive Plants provides basic identification and classification details.
Seedlings can be difficult to distinguish from other plants. Once stinknet bolts and develops flower heads, it is more distinctive in Arizona, but pineappleweed and Australian waterbuttons can be look-alikes. The University of Arizona Cooperative Extension advises careful identification; do not remove a plant based only on a distant photograph if you are unsure.
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Stinknet can grow larger in favorable conditions than it does in dry conditions. Its appearance and patch size therefore vary with the site and season.
What damage can stinknet cause?
It can crowd out native vegetation
Dense stands can overtop native wildflowers and reduce native plant diversity. Where stinknet replaces more palatable plants, it may also reduce available livestock forage. These effects are especially relevant when infestations expand into open desert or other natural areas.
Its seeds can hitchhike
Tiny seeds can travel on shoes, clothing, animal fur, vehicles, and maintenance equipment. Seed heads may remain attached after plants dry. Clean footwear, tools, tires, and other gear before moving from an infested area to an uninfested one. The UC Statewide IPM Program’s stinknet guidance describes seed movement and management considerations.
Is stinknet poisonous or dangerous to touch?
It is not established that every contact is harmful, and regional sources do not support describing stinknet as universally poisonous. The University of Arizona Cooperative Extension reports that people differ in their reactions to its pungent odor and cites reports of respiratory distress and allergic contact dermatitis; it also says potential public-health hazards require further study. A Southwest Vegetation Management Association guide likewise reports possible contact dermatitis and respiratory allergy.
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People with sensitive skin or lungs may choose to wear gloves, long sleeves, or a mask when working near or removing the plant. A local outreach page says stinknet is not toxic to most people, but that is local outreach wording, not a definitive toxicology finding. Avoid burning removed plants: dry material can fuel fire, and smoke may be acrid or irritating.
Does stinknet increase wildfire risk?
Dry standing stinknet can add flash fuel and low-level ladder fuel in desert vegetation. In Arizona, the plant dries as the hot, dry early-summer period begins. The University of Arizona Cooperative Extension describes dense dry stands as capable of carrying fire across sparse ground cover and helping flames reach shrubs or trees.
The distinction between green and dry growth matters: the Extension publication says green stinknet before drying was not noted as a fire hazard. Stinknet does not, by itself, cause a wildfire; it can provide fuel after drying, alongside other invasive cool-season annuals. The broader concern is that native Sonoran Desert plants are generally fire-intolerant, while some invasive weeds can regrow aggressively after burns, as the Southwest Vegetation Management Association guide explains.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How do you get rid of stinknet?
Choose a method based on patch size, plant stage, access, and the risk of harming desirable vegetation. The main practical goal is to stop plants from setting and dispersing seed, then return to check for new growth. The University of Arizona Cooperative Extension identifies preventing seed production as the central management goal.
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| Situation | Approach | Important limitation |
|---|---|---|
| Small patch; plants can be reached safely | Pull the whole plant when soil is moist or loose; shallow hoeing or cultivation can help with early seedlings. | Flowering plants need careful handling and locally appropriate bagging to reduce seed spread. |
| Large or difficult-to-access patch | Consider a repeated mechanical or integrated control plan, or consult a qualified local applicator about site-appropriate options. | Mechanical work may be impractical at scale; herbicide selection and timing depend on the site, label, and plant stage. |
| Patch treated or removed | Inspect again after rain or irrigation and in later growing periods; clean gear before leaving. | Multiple cohorts, seed persistence, and reinvasion mean one treatment may not resolve the infestation. |
Small patches: pull or cultivate early
Where the patch is manageable, pull the whole plant when soil is moist or loose. University of Arizona Cooperative Extension says stinknet does not resprout from root fragments. Wear gloves and long sleeves if you are prone to skin irritation. A garden hoe or shallow cultivator can help with early shallow cultivation or seedling control, but no particular tool is a tested universal solution.
If plants are flowering, check local disposal guidance and bag them when advised. The Stinknet Stay Away / Tucson Audubon collaborative project advises bagging flowering plants to reduce seed spread. Avoid dragging seed-bearing plants through clean areas.
Larger patches: plan for repeated control
As a patch grows, hand removal can become impractical. UC IPM describes repeated mechanical treatment and notes that herbicide options may be needed for large populations. Postemergence herbicide treatments generally work best during the rosette or bolting stages, before flowering; results can be inconsistent later. Preemergence approaches depend on rain or irrigation and can affect non-target plants.
Herbicide use is label- and site-specific. Read and follow the current product label, use the required protective equipment, and make sure the product is appropriate for the land use and surrounding plants. The University of Arizona recommends considering a licensed applicator, particularly where the site is sensitive or the infestation is extensive. No single product or rate is appropriate for every location.
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How do you prevent stinknet from spreading back?
- Remove or control plants before they set seed where practical.
- Bag flowering plants when local guidance recommends it, and avoid moving seed heads through clean areas.
- Clean seeds and soil from boots, clothing, tools, tires, pets, and maintenance equipment before leaving an infested site.
- Revisit the area after rainfall or irrigation and during later growth periods; new cohorts may appear after an initial treatment.
- Continue monitoring over multiple years where an infestation has been established, since reinvasion and persistent seed can make a one-time effort insufficient.
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