Giant Hogweed (Heracleum mantegazzianum) is a large plant, but although grand and showy in its appearance, it is an invasive plant that you don’t want to touch. Also in the same family, Apiaceae – the carrot family, is wild parsnip (Pastinaca sativa), another invasive species to avoid. Both plants contain chemicals that can cause a toxic skin reaction when humans encounter the plant’s sap.
Furanocoumarins, when combined with sunlight, can cause phytophotodermatitis, a serious skin inflammation. The chemical prevents the skin from protecting itself against sunlight, which can lead to a severe sunburn. The reaction can be as mild as skin discoloration or as severe as large, painful blisters. The effects of giant hogweed can be much worse than that of wild parsnip, with some blisters similar to third-degree burns, permanent scarring, discoloration of the skin, increased sensitivity to sunlight that may last for years, and contact with the eyes could lead to blindness.
Giant hogweed was introduced to the United States in the early 1900s. as an ornamental. One of the first plantings was in gardens near Highland Park in Rochester. It escaped cultivation and has now become established in the Northeast and parts of Canada.
• White flowers clustered into an umbrella-shaped flower cluster, up to 2.5 feet across, blooms between June and July (note: plant generally produces a flowering stalk in 3 to 5 years but can take up to 8 years or more)
• Between 7 to 14 feet tall with huge leaves, incised and deeply lobed, up to 5 feet across
• Stems are green with purple splotches and coarse white hairs, 2-4 inches in diameter
• Seeds are dry, flattened, oval and approximately 3/8-inch-long and tan with brown lines
Except for its towering size, giant hogweed can easily be mistaken for other umbrel plants.
If you see Giant Hogweed, keep your distance, and take high-resolution photos of the entire plant, stem, leaves, flowers and/or seeds. Photos and detailed directions to the infestation can be emailed to DEC at email@example.com or contact your local Cornell Cooperative Extension office for assistance with identification.
DEC crews visit each confirmed infestation site of giant hogweed and use an appropriate control method for the size of infestation and location. This service is free of charge to the landowner. Sites are visited each year until the plants are eradicated. For sites to be monitored and controlled, the landowner must give annual permission.
Wild Parsnip is native to southern and central Europe and was possibly brought to North America as a root crop by colonists as early as the 1600s. It has become established throughout the northern United States and southern Canada.
• Yellow flowers clustered into an umbrella-shaped flower cluster, 4-6 inches wide, blooms between May to mid-July (note: flowering usually occurs during the second year of growth)
• Between 2 to 5 feet tall with yellowish-green leaves with 5 to 15 toothed and variably lobed leaflets
• Stems are yellowish-green with vertical grooves
• Seeds are flat, brown, and slightly winged
Both plants can be found growing on roadsides, fields, pastures, along trails, any place where the soil has been disturbed, and along streams and rivers.
If you see Wild Parsnip, manual removal of plants can be effective for new infestations and small areas. When removing plants, wear gloves, long-sleeved shirts, pants, boots, and eye protection to prevent contact with the sap. Synthetic, water-resistant materials are recommended. Before the plant going to seed, cut the root 1-2 inches below the soil or pull by hand. If removing the plants after they have gone to seed, cut off the seed head and place it in a plastic bag. Leave the bags in the sunlight for one week to kill the seeds before disposal. Mowing only after it has flowered, but before it goes to seed, can kill the plant. When mowing, take precautions to prevent sap from contacting skin and eyes. Clean all protective clothing, gear, tools, and equipment thoroughly. Herbicides such as glyphosate or triclopyr can be applied as spot treatments; follow product labels carefully. Monitor the area long-term for seedlings emerging from the seed bank.
What to do if you come in contact with these plants? Immediately wash the area with soap and COLD water and keep the area away from sunlight for 48 hours. If a reaction occurs, see a physician.