In the Garden:
New England
June, 2010
Regional Report

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3476

Giant hogweed is public enemy #1- don't touch this plant without protection!

Giant Hogweed- Don't Touch This Plant!

Those of you of a certain age may remember a scene from that 1950's movie classic, Invasion of the Body Snatchers. As the extra-terrestrial pod people close in, there's a close-up of a man's frantic face as he shouts into the camera "They're here already!"

That's the way I feel when I read about the invasion of a plant that certainly seems like it could be an alien life form. Giant hogweed (Herecleum mantegazzianum) is a monstrous plant, both in size and attributes, a towering invader that can cause severe skin and eye irritation, painful blisters, permanent scarring, even blindness to those who inadvertently come in contact with its sap. This noxious weed has become widely established throughout our region. While agencies in the New England states and New York work to eradicate stands of this plant, it's important that gardeners and anyone else who might encounter it clearing land or even just walking along a stream or roadside be able to identify it and avoid coming into unprotected contact with it.

So where did this botanical terror come from? Originally from the Caucasus Mountain region between the Black and Caspian Seas in Eurasia, it was brought first to Europe in the late nineteenth century and then to the US in the early twentieth century as, if you can believe this, an ornamental plant- cultivated perhaps by gardeners in full body armor? It quickly escaped from cultivation and is now found in many areas of the U.S. It is especially abundant in New England, New York, Pennsylvania, and the Pacific Northwest.

Giant hogweed is true to its name. A biennial or perennial carrot family member, it produces huge, flat-topped clusters of white flowers up to 2½ feet across in late spring to midsummer, atop stems that can reach as high as 15-20 feet! Think Queen Anne's lace on steroids! Its hollow ridged stems are 2 to 4 inches across and are covered with purple blotches and coarse white hairs. The large, tropical-looking compound leaves can be 5 feet wide.

A vigorous grower that prefers moist soil, giant hogweed is especially prevalent along streams and rivers, where it often forms large stands that out-compete the native vegetation. As the existing flora is overwhelmed, there is often an increase in stream bank erosion. You may also encounter giant hogweed in roadside ditches, railway beds, vacant lots or other disturbed areas where the soil is moist.

Although giant hogweed does have a detrimental ecological impact, its biggest menace by far is as a public health hazard from the irritating sap that is present in all parts of the plant. If your moist skin (and even perspiration will do) comes into contact with the sap and is then exposed to sunlight, severe, burn-like irritation develops, usually within 1 to 3 days, that can cause permanent scarring. Even a tiny amount of sap in your eye can lead to temporary or permanent blindness.

Just brushing against the leaves won't cause inflammation; you need to have contact with a broken stem or crushed leaf, root, flower or seed. But because the consequences of encountering the sap are so severe, the first rule in dealing with giant hogweed is: Never touch the plants unless you are well-protected! If you think you may have contacted some of the sap, immediately wash your skin thoroughly with soap and water. At the first sign of any irritation, get prompt medical advice.

So what should you do if you find giant hogweed growing on your property? There are a number of other wild plants that could possibly be mistaken for giant hogweed, including cow parsnip, wild parsnip, poison hemlock and angelica. But don't take any chances! Never attempt to eradicate it without first contacting the appropriate state agency to report the stand, get a confirmed identification and information on how to safely eradicate this plant.

Listed below are links with more information and contact information for an appropriate agency for each state in our region:
Maine: http://www.state.me.us/doc/nrimc/mnap/publications/hogweed_homeownerguide.pdf
New Hampshire: http://extension.unh.edu/news/2006/03/beware_the_giant_hogweed.html
Vermont: http://www.uvm.edu/mastergardener/pdf%20files/giant_hogweed_homeowners_brochure__Read-Only_.pdf
Massachusetts: http://www.massnrc.org/pests/pestFAQsheets/hogweed/giant_hogweed.htm
Connecticut: http://www.hort.uconn.edu/cipwg/hog_brochure_%20CTFINAL.pdf
Rhode Island: http://www.dem.ri.gov/programs/bnatres/agricult/pdf/pehogwd.pdf
New York: http://www.dec.ny.gov/animals/39809.html;
http://www.dec.ny.gov/docs/lands_forests_pdf/ghbrochureny.pdf


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