Giant Hogweed

Plants offered for sale or seed traded as an ornamental curiosity - it still circulates occasionally under names like cartwheel flower; and any find on your own or adjacent land, which is what triggers the reporting duty.

Photograph the plant from a safe distance - whole plant, stem, leaf and flower head - note the location, and contact your state department of agriculture or invasive species program. In much of its range a trained crew will treat the site and return for follow-up years, often at no cost.

Never buy, accept, plant or move this species or its seed, and never move soil from an infested site. Check your state noxious weed and quarantine lists, since state obligations often go beyond the federal ones.

Not a horticultural problem but a legal one. Giant hogweed is on the US Federal Noxious Weed List, which makes it illegal to import, sell, or move across state lines, and many states carry their own prohibited or quarantine listing on top of that. Several states also run reporting hotlines and funded eradication programs, and in some a landowner is expected to report or control a find.

Any contact at all - there is nothing to see or feel during the window when action still helps. Then redness and burning appearing about half a day later in streaks where stems brushed skin, followed by fluid-filled blisters, most often on forearms, shins, neck and face.

Get out of the sun at once, wash with soap and cold water, and keep the skin covered from sunlight for at least 48 hours - that shielding is what limits the burn. Do not break blisters. See a doctor for blistering, facial involvement or large areas; severe cases are treated as burns. Sap in the eye needs immediate medical care with the eye shielded from light. Protect healed skin from sun for months to years.

Do not touch, cut, mow, strim, chip or burn it. Keep children and pets away, since hollow stems get used as toys and put sap around the mouth and eyes. If work is unavoidable, full waterproof coveralls, goggles, face shield and gloves taped to the sleeves, on a still overcast day - or hand the site to a state or county crew, which in much of its range is free.

The defining hazard, and the most severe phytophotodermatitis of any plant in North America. Sap from any part on skin later exposed to sunlight causes a delayed chemical burn: no sensation at contact, redness at roughly 15 hours, deep blistering by 48, then slow-healing wounds, dark scarring, and skin that can stay hypersensitive to sunlight for years. Sap in the eye has caused temporary and in some cases permanent blindness. Dry, dead stalks remain phototoxic, so spring cleanup carries the same risk as summer work.

New rosettes appearing downstream or on flood-deposited soil below a known stand; expanding colonies along ditches, rail margins and woodland edges; bare, eroding bank under last year's dead canes.

Root cutting or program-applied herbicide before seed set, with the seed heads bagged and removed, followed by monitoring for around a decade while the seed bank runs down. Replant treated banks with competitive vegetation so bare soil does not persist.

Report and treat upstream stands first - treating downstream while a seed source remains upstream achieves nothing. Never move soil or fill from an infested site, and do not let cut seed heads reach water.

One flowering plant sets tens of thousands of seeds, and they float - so a single stand seeds an entire river corridor downstream. Dense stands shade out everything beneath them, and because the plants die back completely in winter they leave bare riverbank soil through the erosive season, worsening bank collapse and sediment loss.