Giant Hogweed Wrap Up

John Thompson of CRISP

This month, the Catskill Regional Invasive Species Partnership (CRISP) team wrapped up their 2017 giant hogweed (Heracleum mantegazzianum) control season.

CRISP annually partners with the NYS Department of Environmental Conservation to control giant hogweed plants around the Catskills watershed. CRISP staff respond to reports of giant hogweed in the region, and kill the plant when it occurs. This year CRISP staff responded to 13 infestations, and removed approximately 750 stems of this dangerous invasive over the 3.2 million acres of the CRISP region.

Giant hogweed, native to the Caucasus region of Southern Russia, is a highly dangerous invasive plant. It was intentionally introduced to the United States for garden use, and since the 1900’s, has readily spread across the East and West coasts of the United States. This plant has become notorious around the US for its dangerous sap and immense growth form.

Nico Hogweed.jpg

The sap of giant hogweed is famous for causing extreme photodermatitis. It contains a chemical called furanocoumarin, which binds with DNA in skin. After exposure to ultraviolet light from the sun, cell death occurs, which can be expressed as severe burns and blisters. In rare cases, exposed skin can remain sensitive to the sun in this manner for several years. If it is exposed to the eyes, the sap can also cause blindness.

Treatment for exposure involves cleaning the potentially affected skin as soon as possible with soap and water, and keeping subsequent sun exposure to a minimum for a few days. Seek medical advice as soon as possible if inflammation occurs; it is also possible that prescription steroid creams can help reduce the damage.

H. mantegazzianum grows to be roughly 16 feet tall, with large deeply lobed and jagged leaves up to 5 feet wide, though it can take several years to grow this big. Its flowers grow in a large umbrella shape up to 3 feet in diameter. Young hogweed plants can be confused for a native lookalike in cow parsnip (Heracleum maximum). Luckily, you can tell the two apart in several ways. In addition to giant hogweed leaves and flowers growing much larger than those of cow parsnip, hogweed stems will have significant purple splotching, particularly at the leaf nodes, while cow parsnip will typically have a mostly green stem. Giant hogweed will also have conspicuous, coarse white hairs growing at the leaf nodes and undersides of the leaves, while cow parsnip’s hairs will be much finer.

If you think you have seen giant hogweed, or have questions about the plant, please contact