Giant Hogweed Guide, Meaning , Facts, Information and Description
Heracleum mantegazzianum
Giant Hogweed (Heracleum mantegazzianum) is a member of the Parsley or Carrot family, (Apiaceae) and is native of Central Asia.
Many foreign plants were introduced to Britain in the 19th century, mainly for ornamental reasons. A few have become aggressively dominant, creating serious problems in some areas.
One such invasive plant is the Giant Hogweed. It is now widespread throughout the British Isles especially along riverbanks. By forming dense strands they can displace native plants and reduce wildlife interests.
In the UK the Wildlife and Countryside Act 1981 makes it an offence to plant or cause Giant Hogweed to grow in the wild.
As its name indicates, it is characterized by its size and may grow 5-7m (15-20 ft) tall. Except for size, it closely resembles Common Hogweed (Heracleum sphondylium) or Garden Angelica (Angelica archangelica).
It is further distinguished by a stout, dark reddish-purple stem and spotted leaf stalks that are hollow and produce sturdy bristles. Stems vary from 5-10 cm (2"-4") in diameter and the plant has deeply incised compound leaves which grow up to 1.7m (5 ft) in width.
Giant Hogweed is a perennial with tuberous rootstalks which form perennating buds each year. It flowers mid-May through July, with numerous white flowers clustered in an umbrella-shaped head that is up to 0.8m (2.5 ft) in diameter across its flat top.
The plant produces flattened, 1cm (3/8") long, oval dry fruits that have a broadly rounded base, and broad marginal ridges.
Flower heads of giant hogweed can reach 2 ½ feet in diameter, while the smaller cow parsnip seldom exceeds one foot in diameter. Scale is definitely a defining characteristic for giant hogweed. It's tall, broad, and imposing. Each purple spot on the stem surrounds a hair, and there are large, coarse white hairs at the base of the leaf stalk. Leaves, vaguely resembling rhubarb leaves but deeply cut (incised) can be 5 feet across. The huge flower looks like a giant Queen Anne's lace, but the leaves are quite different. Queen Anne's lace has ferny-looking leaves; Giant Hogweed has big, platter-shaped solid leaves. The Giant Hogweed flowers from mid-June to mid-July and then produces large flattened elliptic dry seeds. Shoots die down in the fall. Tall stems mark locations of this weed during winter.
Giant Hogweed is a phototoxic plant. Its sap can cause photodermatitis, skin inflammations when the skin is exposed to sunlight. Initially the skin colours red and starts itching. Then blisters form as in burns. Hospitalisation may become necessary. Presence of minute amounts of sap in the eyes, can lead to temporary or even permanent blindness. These reactions are caused by the presence of linear derivatives of furocoumarine. These chemicals can get into the nucleus of the epithelial cells, forming a bond with the DNA, causing it to die.
Keep children away from this plant. Wear protective clothing when handling it if you dig plants; consider wearing eye protection. Chopping out the root is feasible, but may have to be done several times as the plant re-grows. Wash off exposed skin thoroughly with soap and water.
Keep the plant mowed down during the summer to prevent seeds from maturing. Don't allow pieces of it to land on bare skin. Even after the parent plant is completely removed, the seeds left behind can come up, 7 or 8 years later. Removing the green growth will help to exhaust the root and will weaken the plant, so digging it out and chopping it is feasible.
2,4-D, TBA, MCPA and dicamba will kill above ground parts but are reportedly not particularly effective on persistent rootstalks. Glyphosate (roundup) is considered the most effective herbicide and should be used cautiously around desirable species since it is nonselective. Application during bud stage and while the plant is actively growing is recommended by New York Cooperative Extension.