Plant Problem Diagnostic
Deadly Look-Alike Weeds: Poison Hemlock, Giant Hogweed, Wild Parsnip
The short answer
Three common carrot-family weeds deserve a hard do-not-touch rule. Giant hogweed and wild parsnip have sap that, combined with sunlight and moisture, causes severe chemical burns and blistering (phytophotodermatitis); giant hogweed sap in the eyes can cause blindness. Poison hemlock is different: it does not burn skin, but every part of the plant is highly poisonous if ingested, dangerous to people, pets, and livestock.
Quick ID: giant hogweed is enormous, 8 to 15 feet tall, with hairy, hollow, purple-blotched stems and white umbrella flower heads up to 2 feet wide. Poison hemlock is 5 to 12 feet with a smooth (not hairy) purple-blotched stem, ferny finely-dissected leaves, and many small creamy-white umbels. Wild parsnip is 3 to 5 feet with a grooved green stem and flat-topped yellow flower clusters. If you suspect giant hogweed, do not touch it; photograph it from a distance and report it to your state environmental or natural resources agency (in New York, the DEC giant hogweed hotline).
Tell the three apart
- Giant hogweed: 8-15 ft tall; stems hairy, hollow, with purple blotches; huge jagged, deeply lobed leaves; white umbel flower heads up to 2 ft across. Sap causes severe burns; eye contact can cause blindness.
- Poison hemlock: 5-12 ft tall; stem smooth and waxy with purple blotches, no hairs; leaves finely dissected and fern-like; many small creamy-white umbels 1-3 in across. Deadly if ingested; not a contact-burn plant, but wear gloves anyway.
- Wild parsnip: 3-5 ft tall; grooved green stem without hairs; compound leaves with jagged-toothed leaflets; pale yellow, dill-like umbels. Sap plus sunlight causes bad chemical burns.
- Harmless look-alike: Queen Anne's lace (wild carrot) is much smaller, usually 1-4 ft, with a hairy green stem and often a single dark floret at the flower's center. When in doubt, treat any tall white-umbel plant as suspect.
If skin touches the sap
For giant hogweed or wild parsnip sap: wash the area promptly with soap and water and keep it out of sunlight, because the burn reaction is triggered by UV exposure; New York DEC notes severe burns can develop within 24 to 48 hours of exposure to sap plus sunlight. Cover the area when outdoors and see a doctor if blistering develops or if sap contacted the eyes. For any suspected ingestion of poison hemlock by a person or pet, call Poison Control or a veterinarian immediately; even small amounts can be fatal.
⚠ Never weed-whack or mow these plants; that aerosolizes sap and plant fragments. And never burn poison hemlock: Illinois Extension warns the inhaled smoke can be toxic.
Removing them safely
For small infestations of wild parsnip or poison hemlock on your own property, Illinois Extension advises wearing gloves, long pants, long sleeves, and eye protection, and suggests considering herbicide treatment over mechanical control to minimize sap contact. Wash any contaminated clothing separately from the family laundry. Bag plants rather than composting them, and follow your local guidance for disposal.
Giant hogweed is in a different category: it is a regulated invasive plant, and several states run active eradication programs. Do not attempt removal yourself. Report it.
How and where to report giant hogweed
Photograph the plant from a safe distance, note the location, and contact your state's environmental, agriculture, or natural resources agency, or your county Extension office, which can confirm the ID from photos. In New York, the DEC runs a dedicated giant hogweed hotline (845-256-3111, or ghogweed@dec.ny.gov) and will handle confirmed sites; Illinois Extension directs reports to the Illinois Department of Natural Resources or the local Extension office. Confirmed hogweed populations are typically removed by trained crews at no cost to the landowner.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- University of Illinois Extension - Carrots Gone Bad: Wild Parsnip, Giant Hogweed and Poison Hemlock — Wild parsnip (3-5 ft, yellow umbels) sap causes phytophotodermatitis; giant hogweed (8-15 ft, hairy hollow purple-blotched stems, white umbels to 2 ft) sap causes chemical burns and possible blindness; poison hemlock (5-12 ft, smooth blotchy purple stem, fern-like leaves) is poisonous if ingested and should never be burned; wear gloves, long sleeves, and eye protection, and report suspected hogweed to the state DNR or Extension.
- New York State DEC - Giant Hogweed — Giant hogweed sap combined with sunlight and moisture can cause severe burns within 24 to 48 hours and eye contact can cause blindness; NY residents should report sightings to the DEC giant hogweed hotline (845-256-3111 / ghogweed@dec.ny.gov) with photos taken from a safe distance.
- US Fish & Wildlife Service - Don't Touch These Plants — Giant hogweed and wild parsnip sap cause painful burns and scarring in combination with sunlight; poison hemlock is highly toxic to people and animals if ingested.