--- { "id": "giant-ragweed", "name": "Giant ragweed", "scientific": "Ambrosia trifida", "category": "native", "status": "Native Colorado plant · not on state Lists A/B/C", "status_sources": [ "C-floristic-2020", "CO-rules-2025" ], "warning": "Allergenic pollen and strong competition in disturbed ground", "warning_tone": "caution", "aliases": [ "great ragweed" ], "taxonomy_note": "Giant ragweed is Ambrosia trifida. A mismatched Latin name in the compared manufacturer guide is not adopted. Common ragweed and western ragweed have their own profiles.", "source_ids": [ "C-floristic-2020", "CO-rules-2025", "I-giant-ragweed", "C-ragweed-native", "S27" ], "description": "Giant ragweed: Allergenic pollen and strong competition in disturbed ground. Identification and evidence for Colorado readers.", "claim_evidence": [ { "label": "Identification", "sources": [ "I-giant-ragweed" ], "scope": "Species-specific", "note": "", "id": "giant-ragweed-1" }, { "label": "People", "sources": [ "I-giant-ragweed", "C-ragweed-native" ], "scope": "Species-specific", "note": "", "id": "giant-ragweed-2" }, { "label": "Dogs & cats", "sources": [], "scope": "Review limitation", "note": "", "id": "giant-ragweed-3" }, { "label": "Other animals", "sources": [ "I-giant-ragweed" ], "scope": "Forage observation; safety limitation", "note": "", "id": "giant-ragweed-4" }, { "label": "Plants & habitat", "sources": [ "I-giant-ragweed" ], "scope": "Species-specific", "note": "", "id": "giant-ragweed-5" }, { "label": "Management & timing", "sources": [ "C-ragweed-native" ], "scope": "Species-specific", "note": "", "id": "giant-ragweed-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": "Dogs & cats", "question": "Find species-specific dog and cat exposure evidence; do not infer safety from missing reports.", "related_claim_ids": [ "giant-ragweed-3" ] }, { "area": "Other animals", "question": "Clarify feeding and exposure risks for each animal group; do not transfer findings between species.", "related_claim_ids": [ "giant-ragweed-4" ] }, { "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 32; Ambrosia trifida", "basis": "Included in the 2020 statewide flora assessment. This is not a current county abundance survey.", "source_taxon": "Ambrosia trifida" }, "source": "content/plants/giant-ragweed.md" } --- # Giant ragweed *Ambrosia trifida* **Native Colorado plant · 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) > **Allergenic pollen and strong competition in disturbed ground.** [Exposure help](https://denson.github.io/colorado-weed-field-guide/safety/). **Identification caveat:** Giant ragweed is Ambrosia trifida. A mismatched Latin name in the compared manufacturer guide is not adopted. Common ragweed and western ragweed have their own profiles. ## Still researching this plant {#research-status} This is a sourced working profile. Evidence is incomplete for **Dogs & cats, Other animals**. 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. ![Ambrosia trifida: An upright giant ragweed plant beside a fence, with large three- to five-lobed leaves.](https://denson.github.io/colorado-weed-field-guide/assets/photos/coverage-hazard-photos-ambrosia-trifida-1.jpg) **habit** — An upright giant ragweed plant beside a fence, with large three- to five-lobed leaves. Photo: GTBacchus; [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0); [source record](https://commons.wikimedia.org/wiki/File:Ambrosia_trifida_full_shot.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/9/97/Ambrosia_trifida_full_shot.jpg). Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference, not an independent specimen-based taxonomic determination. Giant ragweed leaves may be simple, three-lobed or five-lobed. The photographs retain the exact source species identification. Wikimedia server-resized derivative; no local crop, colour change or generative editing. Gallery display preserves the full image; catalog preview may use a CSS crop. ![Ambrosia trifida: Large lobed, toothed leaves arranged along a sturdy green stem.](https://denson.github.io/colorado-weed-field-guide/assets/photos/coverage-hazard-photos-ambrosia-trifida-2.jpg) **leaves and stem** — Large lobed, toothed leaves arranged along a sturdy green stem. Photo: Ayotte, Gilles, 1948-; [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0); [source record](https://commons.wikimedia.org/wiki/File:Ambrosia_trifida_15-p.bot-ambro.trifi-08.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/e/e4/Ambrosia_trifida_15-p.bot-ambro.trifi-08.jpg). Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference, not an independent specimen-based taxonomic determination. Giant ragweed leaves may be simple, three-lobed or five-lobed. The photographs retain the exact source species identification. Wikimedia server-resized derivative; no local crop, colour change or generative editing. Gallery display preserves the full image; catalog preview may use a CSS crop. ![Ambrosia trifida: Several tall leafy shoots carrying slender terminal spikes of green flower heads.](https://denson.github.io/colorado-weed-field-guide/assets/photos/coverage-hazard-photos-ambrosia-trifida-3.jpg) **flowering habit** — Several tall leafy shoots carrying slender terminal spikes of green flower heads. Photo: Ayotte, Gilles, 1948-; [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0); [source record](https://commons.wikimedia.org/wiki/File:Ambrosia_trifida_15-p.bot-ambro.trifi-06.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/5/59/Ambrosia_trifida_15-p.bot-ambro.trifi-06.jpg). Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference, not an independent specimen-based taxonomic determination. Giant ragweed leaves may be simple, three-lobed or five-lobed. The photographs retain the exact source species identification. Wikimedia server-resized derivative; no local crop, colour change or generative editing. Gallery display preserves the full image; catalog preview may use a CSS crop. ## Identification An annual with rough stems and opposite leaves, usually with three to five deep lobes. Early leaves may be unlobed. Male flower clusters stand at the stem tips. [I-giant-ragweed](https://crops.extension.iastate.edu/encyclopedia/giant-ragweed) ## People Windborne pollen is a significant hay-fever trigger for susceptible people. Colorado extension describes late-season ragweed exposure; local timing varies with weather. [I-giant-ragweed](https://crops.extension.iastate.edu/encyclopedia/giant-ragweed) [C-ragweed-native](https://sam.extension.colostate.edu/wp-content/uploads/sites/44/2019/08/August-31-2019-Ragweed.pdf) ## Dogs & cats The reviewed sources do not establish species-specific ingestion effects or a safe exposure amount for dogs or cats. Missing evidence does not establish safety. ## Other animals Some animals browse the foliage; that does not establish a safe feed amount or a pet-safety rating. [I-giant-ragweed](https://crops.extension.iastate.edu/encyclopedia/giant-ragweed) *Evidence scope: Forage observation; safety limitation.* ## Plants & habitat Early emergence and tall growth can help it dominate disturbed sites. Resistance to some herbicide groups is documented in particular populations. [I-giant-ragweed](https://crops.extension.iastate.edu/encyclopedia/giant-ragweed) ## Management & timing Remove young plants before flowering and seed formation. For a large or persistent infestation, consult a local weed specialist about identification and resistance. [C-ragweed-native](https://sam.extension.colostate.edu/wp-content/uploads/sites/44/2019/08/August-31-2019-Ragweed.pdf) ## 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. - **I-giant-ragweed** — [Giant ragweed](https://crops.extension.iastate.edu/encyclopedia/giant-ragweed), Iowa State University Extension. Accessed 2026-09-07T02:26:09+00:00. Locator: Named species or genus; identification, distribution and hazard sections where available. - **C-ragweed-native** — [Ragweed](https://sam.extension.colostate.edu/wp-content/uploads/sites/44/2019/08/August-31-2019-Ragweed.pdf), Colorado State University Extension. Accessed 2026-09-07T02:26:09+00:00. Locator: Named species or genus; identification, distribution and hazard sections where available. - **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=giant-ragweed) — 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 32; Ambrosia trifida. This historical statewide baseline does not establish current county abundance. ## Open research questions - **Dogs & cats:** Find species-specific dog and cat exposure evidence; do not infer safety from missing reports. - **Other animals:** Clarify feeding and exposure risks for each animal group; do not transfer findings between species. - **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 Giant ragweed is Ambrosia trifida. A mismatched Latin name in the compared manufacturer guide is not adopted. Common ragweed and western ragweed have their own profiles. 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 | |---|---|---|---|---| | giant-ragweed-1 | Identification | Species-specific | I-giant-ragweed | No quantitative safe exposure established here. | | giant-ragweed-2 | People | Species-specific | I-giant-ragweed, C-ragweed-native | No quantitative safe exposure established here. | | giant-ragweed-3 | Dogs & cats | Review limitation | Review limitation | No quantitative safe exposure established here. | | giant-ragweed-4 | Other animals | Forage observation; safety limitation | I-giant-ragweed | No quantitative safe exposure established here. | | giant-ragweed-5 | Plants & habitat | Species-specific | I-giant-ragweed | No quantitative safe exposure established here. | | giant-ragweed-6 | Management & timing | Species-specific | C-ragweed-native | 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/giant-ragweed/ Content revised: 2026-09-07T02:46:00Z Markdown mirror: https://denson.github.io/colorado-weed-field-guide/plants/giant-ragweed/index.md Text fallback: https://denson.github.io/colorado-weed-field-guide/plants/giant-ragweed/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