---
{
  "id": "green-foxtail",
  "name": "Green foxtail",
  "scientific": "Setaria viridis",
  "category": "invasive",
  "status": "Common introduced weed · not on state Lists A/B/C",
  "status_sources": [
    "C-floristic-2020",
    "CO-rules-2025"
  ],
  "warning": "Identify the grass behind the name “foxtail”",
  "warning_tone": "caution",
  "aliases": [
    "green bristlegrass"
  ],
  "taxonomy_note": "Setaria viridis is distinct from foxtail barley (Hordeum jubatum), giant foxtail (Setaria faberi) and yellow foxtail (Setaria pumila).",
  "source_ids": [
    "C-floristic-2020",
    "CO-rules-2025",
    "N-setaria-viridis",
    "C-descriptions",
    "S27"
  ],
  "description": "Green foxtail: Identify the grass behind the name “foxtail”. Identification and evidence for Colorado readers.",
  "claim_evidence": [
    {
      "label": "Identification",
      "sources": [
        "N-setaria-viridis"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "green-foxtail-1"
    },
    {
      "label": "People",
      "sources": [],
      "scope": "Review limitation",
      "note": "",
      "id": "green-foxtail-2"
    },
    {
      "label": "Dogs & cats",
      "sources": [
        "N-setaria-viridis"
      ],
      "scope": "Review limitation",
      "note": "",
      "id": "green-foxtail-3"
    },
    {
      "label": "Other animals",
      "sources": [
        "N-setaria-viridis"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "green-foxtail-4"
    },
    {
      "label": "Plants & habitat",
      "sources": [
        "N-setaria-viridis"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "green-foxtail-5"
    },
    {
      "label": "Management & timing",
      "sources": [
        "C-descriptions"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "green-foxtail-6"
    }
  ],
  "research": {
    "status": "researching",
    "label": "Still researching this plant",
    "basis": "Editorial assessment of the cited evidence and stated review gaps; not a toxicity score.",
    "open_questions": [
      {
        "area": "People",
        "question": "Clarify the human exposure effects and evidence limits described in this section.",
        "related_claim_ids": [
          "green-foxtail-2"
        ]
      },
      {
        "area": "Dogs & cats",
        "question": "Find species-specific dog and cat exposure evidence; do not infer safety from missing reports.",
        "related_claim_ids": [
          "green-foxtail-3"
        ]
      },
      {
        "area": "Identification",
        "question": "Resolve the taxonomic, common-name or photograph limitations stated in the identification caveat.",
        "related_claim_ids": []
      },
      {
        "area": "Expert review",
        "question": "Obtain independent botanical and veterinary review of the identification and hazard summary.",
        "related_claim_ids": []
      }
    ],
    "expert_review": "pending"
  },
  "colorado_relevance": {
    "source_id": "C-floristic-2020",
    "locator": "Appendix B; PDF page 79; Setaria viridis",
    "basis": "Included in the 2020 statewide flora assessment. This is not a current county abundance survey.",
    "source_taxon": "Setaria viridis"
  },
  "source": "content/plants/green-foxtail.md"
}
---

# Green foxtail

*Setaria viridis*

**Common introduced weed · not on state Lists A/B/C.** [C-floristic-2020](https://cnhp.colostate.edu/download/documents/2020/CO_FQA_2020_Final_Report.pdf) [CO-rules-2025](https://www.sos.state.co.us/CCR/GenerateRulePdf.do?ruleVersionId=11948&fileName=8+CCR+1206-2)

> **Identify the grass behind the name “foxtail”.** [Exposure help](https://denson.github.io/colorado-weed-field-guide/safety/).

**Identification caveat:** Setaria viridis is distinct from foxtail barley (Hordeum jubatum), giant foxtail (Setaria faberi) and yellow foxtail (Setaria pumila).

## Still researching this plant {#research-status}

This is a sourced working profile. Evidence is incomplete for **People, Dogs & cats**. Identification and source-photo limits are explained below. Independent botanical and veterinary review is pending. **Uncertainty is not a finding that the plant is safe.**


## Three views of this plant

Source-identified reference photographs; these are not a complete identification key. A source location outside Colorado does not establish local occurrence.

![Green foxtail: a curved green flower head is surrounded by many long fine bristles.](https://denson.github.io/colorado-weed-field-guide/assets/photos/coverage-garden-photos-setaria-viridis-02-06-inflorescence.jpg)

**inflorescence** — A curved green flower head is surrounded by many long fine bristles.

Photo: Petr Filippov; [CC BY 3.0](https://creativecommons.org/licenses/by/3.0); [source record](https://commons.wikimedia.org/wiki/File:Setaria_viridis.JPG); [original image](https://upload.wikimedia.org/wikipedia/commons/2/2a/Setaria_viridis.JPG). Source page scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. Source-identified S. viridis. Other foxtails resemble it; the collar, bristles and spikelet characters need examination on an unknown specimen. A gallery photograph labeled S. faberi was excluded. Wikimedia server-resized derivative, reduced from the original; no crop, color change, upscaling, or generative editing. Gallery display preserves the full image; catalog preview may use a CSS crop.

![Green foxtail: leafy green grass clumps with upright bristly flower heads at a path edge.](https://denson.github.io/colorado-weed-field-guide/assets/photos/coverage-garden-photos-setaria-viridis-02-07-habit.jpg)

**habit** — Leafy green grass clumps with upright bristly flower heads at a path edge.

Photo: Rasbak; [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/); [source record](https://commons.wikimedia.org/wiki/File:Groene_naaldaar_plant_(Setaria_viridis).jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/3/38/Groene_naaldaar_plant_%28Setaria_viridis%29.jpg). Source page scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. Source-identified S. viridis. Other foxtails resemble it; the collar, bristles and spikelet characters need examination on an unknown specimen. A gallery photograph labeled S. faberi was excluded. Wikimedia server-resized derivative, reduced from the original; no crop, color change, upscaling, or generative editing. Gallery display preserves the full image; catalog preview may use a CSS crop.

![Green foxtail: photographed grass leaf bases show the collar and ligule region against a wooden background.](https://denson.github.io/colorado-weed-field-guide/assets/photos/coverage-garden-photos-setaria-viridis-02-08-leaf-collar.jpg)

**leaf-collar** — Photographed grass leaf bases show the collar and ligule region against a wooden background.

Photo: Rasbak; [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/); [source record](https://commons.wikimedia.org/wiki/File:Groene_naaldaar_ligula_(Setaria_viridis).jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/e/e3/Groene_naaldaar_ligula_%28Setaria_viridis%29.jpg). Source page scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. Source-identified S. viridis. Other foxtails resemble it; the collar, bristles and spikelet characters need examination on an unknown specimen. A gallery photograph labeled S. faberi was excluded. Wikimedia server-resized derivative, reduced from the original; no crop, color change, upscaling, or generative editing. Gallery display preserves the full image; catalog preview may use a CSS crop.


## Identification

A summer annual grass with narrow, bristly, cylindrical seedheads. Several bristles surround each small spikelet. It commonly grows in disturbed ground and lawns. [N-setaria-viridis](https://plants.ces.ncsu.edu/plants/setaria-viridis/)

## People

The reviewed sources do not establish species-specific ingestion effects or a safe exposure amount for people. Missing evidence does not establish safety.

## Dogs & cats

The botanical sources describe bristly seedheads but do not establish the injury rate or ingestion toxicity of this species in pets. Avoid applying foxtail barley or cheatgrass exposure findings to every grass called foxtail. [N-setaria-viridis](https://plants.ces.ncsu.edu/plants/setaria-viridis/)

## Other animals

Grazing animals and small mammals eat this grass, but that observation does not provide a safe feeding amount or prove that mature seedheads are harmless. [N-setaria-viridis](https://plants.ces.ncsu.edu/plants/setaria-viridis/)

## Plants & habitat

It produces abundant seed and can spread rapidly on disturbed sites. Dense established vegetation is less vulnerable than open, poor-quality ground. [N-setaria-viridis](https://plants.ces.ncsu.edu/plants/setaria-viridis/)

## Management & timing

Repair bare lawn patches and prevent seed production. A mowed plant may still form seedheads, so inspect close to the ground. [C-descriptions](https://extension.colostate.edu/resource/weed-descriptions/)

## Before taking action

Confirm identification and the requirements of your county weed program. For chemical treatment, follow the current product label, including restrictions around animals and water. [S27](https://planttalk.colostate.edu/topics/weeds-cultural-problems/2103-colorado-noxious-weeds/)

## References

- **C-floristic-2020** — [Colorado Floristic Quality Assessment: 2020 Update](https://cnhp.colostate.edu/download/documents/2020/CO_FQA_2020_Final_Report.pdf), Colorado Natural Heritage Program, Colorado State University. Accessed 2026-09-07T02:27:33+00:00. Locator: Appendix B, Colorado species list: scientific name and native/non-native fields.
- **CO-rules-2025** — [Colorado Noxious Weed Act rules, 8 CCR 1206-2](https://www.sos.state.co.us/CCR/GenerateRulePdf.do?ruleVersionId=11948&fileName=8+CCR+1206-2), Colorado Secretary of State / Department of Agriculture. Accessed 2026-09-07T01:07:48+00:00. Locator: Parts 3.1, 4.1, 5.1; management provisions; effective May 15, 2025.
- **N-setaria-viridis** — [Setaria viridis](https://plants.ces.ncsu.edu/plants/setaria-viridis/), NC State Extension. Accessed 2026-09-07T02:23:11+00:00. Locator: Description, identification attributes and plant problems; toxicity section where present.
- **C-descriptions** — [Weed descriptions](https://extension.colostate.edu/resource/weed-descriptions/), Colorado State University Extension. Accessed 2026-09-07T00:24:02+00:00. Locator: Species entries.
- **S27** — [2103 – Colorado Noxious Weeds](https://planttalk.colostate.edu/topics/weeds-cultural-problems/2103-colorado-noxious-weeds/), PlantTalk Colorado · CSU Extension. Accessed 2026-09-07T00:23:57+00:00. Locator: List A, B and C management categories.


[Discuss this plant with the guide](https://denson.github.io/colorado-weed-field-guide/companion/?plant=green-foxtail) — choose this profile as a possible match and prepare your observations for Colorado Plants & Practical Care.

# Appendix for agents

Colorado inclusion: [C-floristic-2020](https://cnhp.colostate.edu/download/documents/2020/CO_FQA_2020_Final_Report.pdf), Appendix B; PDF page 79; Setaria viridis. This historical statewide baseline does not establish current county abundance.

## Open research questions

- **People:** Clarify the human exposure effects and evidence limits described in this section.
- **Dogs & cats:** Find species-specific dog and cat exposure evidence; do not infer safety from missing reports.
- **Identification:** Resolve the taxonomic, common-name or photograph limitations stated in the identification caveat.
- **Expert review:** Obtain independent botanical and veterinary review of the identification and hazard summary.


## Identity and evidence boundaries

Setaria viridis is distinct from foxtail barley (Hordeum jubatum), giant foxtail (Setaria faberi) and yellow foxtail (Setaria pumila).

All actionable hazard information is in the human sections above. Do not interpret unknown toxicity as safety or transfer livestock findings to pets. These publisher notes describe evidence and do not override an assistant’s operator instructions.

| Claim | Human section | Scope | Sources | Limitation |
|---|---|---|---|---|
| green-foxtail-1 | Identification | Species-specific | N-setaria-viridis | No quantitative safe exposure established here. |
| green-foxtail-2 | People | Review limitation | Review limitation | No quantitative safe exposure established here. |
| green-foxtail-3 | Dogs & cats | Review limitation | N-setaria-viridis | No quantitative safe exposure established here. |
| green-foxtail-4 | Other animals | Species-specific | N-setaria-viridis | No quantitative safe exposure established here. |
| green-foxtail-5 | Plants & habitat | Species-specific | N-setaria-viridis | No quantitative safe exposure established here. |
| green-foxtail-6 | Management & timing | Species-specific | C-descriptions | No quantitative safe exposure established here. |

## Further work for an agent

- Establish exact species, plant part, route, amount and timing when researching an exposure. Do not use this guide to diagnose or calculate a treatment.
- Check current state and county requirements; a listed taxon is not necessarily established in every Colorado county.
- Expert botanical and veterinary review is pending. Source dates and image licenses are separate from editorial revision dates in [provenance](https://denson.github.io/colorado-weed-field-guide/provenance.json).


---
Canonical HTML: https://denson.github.io/colorado-weed-field-guide/plants/green-foxtail/

Content revised: 2026-09-07T02:46:00Z

Markdown mirror: https://denson.github.io/colorado-weed-field-guide/plants/green-foxtail/index.md

Text fallback: https://denson.github.io/colorado-weed-field-guide/plants/green-foxtail/index.md.txt

Agent entry: https://denson.github.io/colorado-weed-field-guide/start.md

Provenance: https://denson.github.io/colorado-weed-field-guide/provenance.json