Giant Hogweed Heracleum mantegazzianum (printable version pdf.)

Giant hogweed is a large flowering perennial (live for more than two years) that may cause severe skin irritations. Contacting the sap of this plant may increase the sensitivity of some people's skin to sunlight. The resulting dermatitis is more like a burn than a rash and is sometimes referred to as false or artificial sunburn causing painful, burning blisters. Blisters or blotches are likely to develop when sap comes into contact with moist skin in the presence of sunlight. People that have come in contact with this plant have reported symptoms that continue for months!

CONTROL Cutting off the flower heads before they go to seed will prevent the plant from self sowing. If cutting back the plant after seeds have formed, it is important to avoid scattering the seeds. Cut plants after sunset and launder clothing that comes into contact with plant juices. But the roots of the plant may persist and grow. The chemical glyphosate(Roundup) is effective in controlling hogweed. Glyphosate is a non-selective herbicide and will kill any adjacent plants that it comes in contact with.

SIMILAR PLANTS Giant hogweed is a member of the carrot family (Apiaceae). Plants that flower at the same time and may be confused with giant hogweed include Angelica, Cow Parsnip, Wild Parsnip, and Common Elderberry. Giant hogweed is distinguishable by its large size, over 6 foot tall, and purple spots on the stem. Only the sap of Wild Parsnip may also cause skin sensitivity in the sun. Click on the pictures below to see larger image.

Download a printable fact sheet, Identification and Control of Giant Hogweed developed by Cornell Cooperative Extension, Broome County.

Plants commonly confused with Giant Hogweed
CLICK ON PICTURES FOR FULL SIZE IMAGE.

		Angelica Angelica atropurpurea		Cow Parsnip Heracleum maximum		Giant Hogweed Heracleum mantegazzianum		Wild Parsnip Pastinaca sativa var. sativa		Common Elderberry Sambucus canadensis
Height
		Height 4-6'		Height 4-9'		Height 6-12'		Height 2-5'		Height 2-10'
Flower Cluster
		White, round, 8-12" wide, July		White, flat 4-8" wide, July-August		White, flat, up to 20" , July		Yellow, flat, 4-6" wide, July-August		White, flat 4-6"wide, July
Stem
		hairless purple stem		Grooved, hairy, mostly green		Hairy, thick, purple spots		Grooved & yellow-green		Woody, grey-brown
Leaf
		Double compound leaf		lobed and toothed, in three segments, 6-18" wide		Lobed leaf, 2-5' wide		Yellow-green, 5-11 leaflets		5-7 leaflets, 2-6" long
		Angelica		Cow Parsnip		Giant Hogweed		Wild Parsnip (more photos)		Common Elderberry

	Wild Chervil Anthriscus sylvestris		Water Hemlock Cicuta maculata		Queen Anne's Lace Daucus carota
Height
	Height 1-4'		Height 4-7'		Height 1-3'
Flower Cluster
	White, flat topped, 2-4", early June		White, half round, 2-8", late July		White, flat 3-6" wide , July
Stem
	furrowed hairy, green		Smooth & purple		Thin hairy stems
Leaf
	Fernlike, double compound		Double compound leaf		Finely dissected, up to 6"
	Wild Chervil (distinguish from poison hemlock)		Water Hemlock		Queen Anne's Lace

Wild Parsnip, Pastinaca sativa var. sativa

Wild Parsnip, is of special concern due to its ability to cause phyto-photo-dermititis (severe sun burn on exposed skin) and its extensive spread along roadways in the southern tier of New York. Wild parsnip is a biennial. During the first summer it appears as a rosette of leaves close to the ground. The following year, it sends up a single flower stalk that holds clusters of yellow flowers in flat-topped, umbel. The flower stalks can grow to be more than 4-feet tall. New York State Department of Agriculture and Markets CAPS program (Cooperative Agricultural Pest Survey) is currently identifying locations of Giant Hogweed, however, wild parsnip is not currently being surveyed.

A very effective control method is to cut the entire root just below ground level with a sharp shovel or spade. Cutting below ground level prevents re sprouting. In some soil types in wet conditions, the plants can be pulled out of the ground by hand. All seeds must be removed from the site and disposed of in a landfill or by burning. If the population is too large to hand-cut or pull, a power brush-cutter can be used just after peak flowering and before the seeds set. Plants may re sprout when cut above the ground, and should be cut again a few weeks later to prevent flowering. Cutting after seed set will greatly reduce the likelihood that the plants will be able to re sprout and flower. Plants cut at this time must all be gathered and removed from the site to prevent mature seed from developing and falling to the ground. Another effective way to eliminate re seeding is to hand-collect all seeds after they have set. If control of flowering or seeding plants is carried out over several years, the population will decrease as the seed bank is depleted.

Mostly green stem of wild chervil	Paired seeds of wild chervil

Wild Chervil, also known as cow parsley, looks very similar to poison hemlock.

However, wild chervil can be identified by two distinct features. The stems of wild chervil are mostly green, while poison hemlock has purple spots. Also, wild chervil flowers each produce two joined seeds. Poison hemlock produces just one. Wild chervil is listed as a noxious weed by some states.

Pesticide recommendations are for informational purposes only and manufacturers' recommendations change. Read the manufacturers' instructions carefully before use. Cornell Cooperative Extension and Cornell University assumes no responsibility for the use of any pesticide or chemicals.