Giant Hogweed

(This 1060th Buffalo Sunday News column was first published on July 17, 2011.)

Giant Hogweed photo from the NYS DEC website

It has been some time since I have written about the most dangerous plant in our environment. I return to the topic here to warn readers again.

A dangerous plant? Seems hard to accept, doesn't it? But then think of poison ivy, the source of a rash that leads to much discomfort, and for some people with special sensitivity, more serious problems. Or ragweed, one of the causes of hay fever (allergic rhinitis), the body's defensive reaction to pollen that some people suffer through usually in fall. Still worse are toadstools and poison hemlock whose toxins, when ingested, can kill.

Certainly those plants with their individual dangers are nothing to sneeze about (pun intended), but they do not measure up to the very real problems associated with another plant, the giant hogweed. Just touching this plant can cause serious injury and if the plant is manhandled, it can even blind you.

Like too many of us nowadays, I knew nothing at all about giant hogweed, but then a reader called to tell me about her experience with it. Joyce French of Marilla told me how she found a huge plant along a rural road. It looked to her like a monster version of wild carrot, the plant most of us know as Queen Anne's lace. On this eight foot tall plant, the white doily of flowers was ten times the width of the wild carrot's umbel: it was over two feet across. And the leaves were equally outsized, appearing like yard-long green fans. The stem too was big: it was two inches thick. It had to be to hold up those leaves and flowers.

Unfortunately for her, Ms. French wanted to learn more about this unusual plant and in the process got some of the hogweed sap on her arms.

She called Richard Zander, then botany curator at the Buffalo Museum of Science, to find out more about the plant. He identified it as giant hogweed (Heracleum mantegazzianum) and warned her not to touch it as it is poisonous.

Too late. Ms. French had as yet had no symptoms when she called Dr. Zander, but within hours she developed serious burns and blisters on her arms. The Buffalo Poison Control Center warned her to protect her arms from the sun and even neon lights for at least the remainder of the summer, because the sensitivity to which she had been exposed would not soon go away.

It turns out that the giant hogweed's sap is phytophototoxic. That jawbreaker is easily parsed: phyto = plant, photo = light and toxic = poisonous. The sap sensitizes the skin to ultraviolet light and subsequent exposure triggers the burns and blisters.

Both the sensitivity and the trigger are necessary: if Ms. French had not been exposed to ultraviolet light, she would not have suffered. But how was she (or anyone else for that matter) to know. And could an individual manage that even if forewarned.

Of course, no one should handle this plant without at least gloves. And those gloves should then be thoroughly cleaned, because they would carry the sap. One of the worries about hogweed is the possibility of a child cutting a section of the hollow stem to use as a kind of pea-shooter. You can imagine the facial damage from such an act.

Where did this alien monster come from? This relative of cow-parsnip, angelica, carrot and celery is native to the Caucasus region of Central Asia. It was introduced to the gardens of European countries and then to the United States and Canada in the 1800s as an unusual and oddly attractive exotic, which of course it is. But like so many garden plants, it escaped to the wild where in a few locations it has thrived. Some New York sites have been found with over 400 of these monsters.

After learning about giant hogweed, I came across several in a field next to a home where a small child was playing. I tried to warn the child's mother, but she told me to mind my own business. I didn't: I reported the plants and local highway workers later removed them.

The New York Department of Environmental Conservation has a hogweed hotline, 845-256-3111, with associated staff members who are removing these dangerous weeds when they are located.-- Gerry Rising