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Watch out for noxious weeds

August 6, 2013
By Hilary Smith ( , Adirondack Daily Enterprise

You may be familiar with poison ivy, the famous glossy, three-leaved plant known for igniting itchy, swollen skin irritations. A native of the Adirondacks, poison ivy is relatively limited in its distribution but is expected to be on the move as temperatures warm. Two other noxious plants that may be less familiar are giant hogweed and wild parsnip. They are not native to the Adirondacks and are becoming more widespread. They pack a punch. To avoid injury, watch out for these invasive plants that are harmful to human health.

Giant hogweed (Heracleum mantegazzianum) is a federally listed noxious plant. Its sap, in combination with moisture and sunlight, can cause severe skin and eye irritation, painful blistering, permanent scarring and blindness. Contact between the skin and the sap occurs either through brushing against the bristles on the stem or breaking the stem or leaves.

As the name suggests, there is nothing small about this plant. Giant hogweed grows to 14 feet. Its deeply lobed, compound leaves span up to 5 feet, and its hollow, ridged stems grow 2 to 4 inches in diameter. The markings on its stem - dark reddish-purple blotches and coarse white hairs - are one of the best ways to distinguish hogweed from native look-alikes, such as cow parsnip and purple angelica. Broad, umbrella-shaped white flowers bloom in July, reaching 2-and-a-half feet in diameter.

Article Photos

Giant hogweed is a noxious invasive plant that grows to 15 ft. At least 10 infestations are known in the Adirondacks.

Giant hogweed arrived in the U.S. in the early 1900s from the Black and Caspian Seas, where it is native. Unfortunately, since then, it has been widely traded among gardeners for its striking stature. Seeds are transported through infected soils and waterways. Infestations are found along streams and rivers and in fields, forests, yards and roadsides throughout New England, the Mid-Atlantic region and the Northwest. Hogweed prefers open sites with abundant light and moist soil, but it can grow in partially shaded habitats, too.

Another noxious plant to look out for is wild parsnip (Pastinaca sativa), which has exploded in distribution in recent years. Infestations are predominantly along roadsides and in waste areas, abandoned fields and pastures, though some infestations are near public use areas, such as campgrounds, playgrounds and trailheads.

Similar to giant hogweed, wild parsnip causes painful blistering. It blooms in July with flat-topped clusters of yellowish-green flowers. It reaches 5 feet tall and has a hairless green stem with vertical grooves and compound leaves.

If you think you have either of these plants on your property, there are several steps to take. First, do not touch it. If you come into contact with them, immediately wash the affected area thoroughly with soap and water and keep the area away from sunlight for 48 hours. See your physician if you think you have been burned by giant hogweed in particular.

If you need help with plant identification, take high-resolution photos of the entire plant, stem, leaves, flowers and seeds, making sure to keep a safe distance. Email the Adirondack Park Invasive Plant Program's (APIPP) terrestrial coordinator Brendan Quirion at or call 518-576-2082.

Once identification is confirmed, infestations can be controlled with the proper methods and gear, including long sleeves and pants, rubber gloves, and for giant hogweed, face protection. Digging or cutting the root of wild parsnip below ground level can be effective. In some soils it can be pulled. Giant hogweed is more difficult and dangerous to remove due to its size, but it can be eliminated after repeated control efforts. It is best to start control projects early in the growing season before seeds set. All plant material should be tightly bagged and sealed and disposed of at a landfill.

If giant hogweed is on your property, APIPP may visit to assess the site and discuss management options. If wild parsnip is located in areas of public use, notify local officials to alert them to this human health hazard. Finally, always avoid picking wildflowers growing along a roadside, which may contain wild parsnip, giant hogweed or other invasive plants. Additional information can be found online at


Eye on Invasives is a biweekly column that spotlights a top invader when it is easiest to identify. Hilary Smith directs the Adirondack Park Invasive Plant Program, a partnership program housed at the Adirondack Chapter of The Nature Conservancy in Keene Valley. Find out more about this award-winning program online at



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