Invasive Giant Hogweed: Beware, But Don’t Sell Your House Yet!

Posted in Science on July 6 2011, by Gregory Plunkett

From the recent news reports, you’d think that New Yorkers had better fly south to escape the onslaught of the diabolical giant hogweed. Even its name evokes a sort of dread, and we are reminded of the stories of “killer bees” from the 1990s.

The giant hogweed plant (know scientifically as Heracleum mantegazzianum) is native to the Caucasus, a mountainous region that separates Europe from Asia. Like so many invasive plants, this species was originally imported to North America as a garden ornamental. It’s easy to see why. The plant is an attractive, gigantic herb, reaching up to ten feet tall in just a few months, topped by huge, umbrella-like spreads with hundreds of tiny white flowers. As a consequence, each plant can make hundreds or even thousands of seeds. Inevitably, this exotic species started to jump garden fences. In our region, the plant was first introduced to Rochester, N.Y. sometime before 1920. Since then, it has been steadily colonizing New York State (see the DEC map here) and it is now approaching New York City.

Why all the fuss? Well, it turns out that giant hogweed produces a sap containing some nasty chemicals called “furanocoumarins”. These compounds easily pass into our skin cells and bind to the DNA inside. Once inside the skin, one additional ingredient is needed to activate the toxin: sunlight. Exposed to the sun, these chemicals kill the affected cells, resulting in a reaction called phytophotodermatitis. This is a nasty, itchy rash that causes discoloration of the skin (from red to dark purple) that can last for months or even years. In severe cases, it can progress, turning into large blisters that mimic second-degree burns. If the plant’s sap reaches the sensitive tissue of your eyes, this blistering could result in scarring and blindness. Yet, as bad as this rash can be, furanocoumarins have been used medicinally as a remedy for psoriasis (where it prevents cell proliferation) and vitiligo (where it darkens depigmented skin).

Most victims of giant hogweed are affected while working in weedy patches, where they are exposed directly to the sap while removing plants by hand or cutting them down using a weed-whacker or lawn mower. The good news: we have expert advice from http://www.backyardboss.net/best-string-trimmer-reviews/, their blog gave us real insight. Giant hogweed is easy to see (it’s ten feet tall, after all), and you must be exposed to both the sap and sunlight. As a result, there are two ways to prevent this nasty rash: avoid exposure to the plant, especially its sap by wearing long pants, long-sleeved shirts, and protective eyewear in areas where giant hogweed grows (unlike the NYS DOT workers above), and avoid exposure of your skin to the sun for the next few days if you do accidentally touch it.

As it turns out, giant hogweed is not the only plant that can cause phytophotodermatitis. Many of its relatives in the plant family Umbelliferae also produce furanocoumarins, including carrots, parsnips, fennel, and celery, but the level of toxins in these species are typically lower. The same family includes other toxic plants, such as poison hemlock, as well as many useful herbs and spices like dill, parsley, cilantro/coriander, and caraway. The same class of compound are produced in completely unrelated plants, too, such as the wild relatives of tomatoes and strawberries, and in the rinds of lemons and limes. You may have heard of the dangers of making lemonade in the sunshine!

Finally, before you sell the house in New York and move to Florida, remember that we have already learned to deal with other nasty plants that cause terrible skin rashes and even blindness, including poison ivy and stinging nettles. Even though these native plants are harder to recognize, we have learned to deal with them. And one last reminder before you sell you house and head for Florida: We New Yorkers may have to deal with snow and giant hogweed, but at least we don’t have alligators, fire ants, and killer bees!