Beware the Giant Hogweed!

Spectacular plant may cause nasty burns

 

When she saw the stately flowering plant growing at a plant nursery in Vermont a few summers ago, Lilly Barton had to have some in her own garden. “It was drop-dead gorgeous,” she recalls. The “hogplants” Barton grew attracted so much attention from customers at the greenhouse and greenhouse supply operation Barton operates with her husband in Langdon, “we decided to save the seed and propagate it for sale.”

 

One sunny August day, Barton cut some of the huge seedheads and set them to dry. She’d noticed “the juice from the thick, hollow stems came squirting out and onto my arms, but I didn’t think much about it. I sat down with friends to talk and have a cold drink.”

 

A few hours later, Barton broke out in deep, burning blisters that required intravenous antibiotics and cortisone shots and took a month to heal. “I still have purple scars all over my arms that look like cigarette burns,” she says.

 

A not-so-gentle giant

Consulting botanical texts, Barton’s husband identified the plant as giant hogweed, Heracleum mantegazzianum, a perennial member of the Umbelliferae family of plants that includes the common carrot, parsnip, celery, parsley and dill, as well as the wild Queen Anne’s Lace, the cow parsnip and the deadly hemlock species.

 

Giant hogweed soars to 15 or even 20 feet high, producing spectacular white umbrella-shaped flowers that measure as much as 36 inches across and leaves up to five feet wide. Dispersed by wind, water, small mammals or birds, giant hogweed seeds can remain viable for eight years or more. The clear, watery sap of giant hogweed contains a toxin that, when activated by sunlight, may cause severe blistering like Lilly Barton experienced.

 

Medical reports note cases of temporary or permanent blindness resulting from exposure to hogweed sap, including many cases of children blinded after using the thick, hollow stems as telescopes and peashooters. Veterinary literature also contains reports of grazing animals receiving painful mouth blisters after consuming hogweed.

 

Minor plant pest can pose a serious health threat

On June 1, the state Department of Agriculture, Markets & Food ( NHDAMF ) banned the sale, propagation and transplant of 18 invasive plants, including giant hogweed.

 

Although giant hogweed does not grow rampant and spread rapidly the way some invasive plant species do, Doug Cygan, Invasive Species Coordinator with the NHDAMF says, “It’s by far the worst plant pest when it comes to human health.”

 

Under a grant from the U.S. Department of Agriculture’s Cooperative Agricultural Pest Survey, state officials have begun surveying and mapping sites where giant hogweed grows. So far, Cygan says they’ve found it in Grafton, Sullivan and Rockingham Counties, with unconfirmed reports of four injuries from hogweed sap this summer.

 

Cygan warns property owners and others who think they’ve encountered a giant hogweed to stay away from these plants, keep pets and livestock from grazing on it, and make sure children and pets don’t play around the plants. Medical literature contains reports of people getting burned by playing with cats and dogs who’ve gotten the hogweed sap on their fur.

 

A seductive import

Originally imported by British gardeners from Eurasia in Victorian times, giant hogweed gradually dispersed throughout Europe and began showing up in North American gardens as early as 1917. The plant currently flourishes in the states of Washington, Oregon, Pennsylvania, New York, Connecticut, Maine, Vermont, and Massachusetts.

 

Dr. Alan V. Tasker, who manages the U.S. Department of Agriculture’s National Noxious Weed Program, says in states like Pennsylvania , where authorities have inaugurated vigorous public awareness and hogweed eradication programs, “Most reports of giant hogweed turn out to be Cow Parsnip, Angelica, or some other [member of the carrot family].”

 

Tasker says people can distinguish giant hogweed from other species of the carrot family, not only by its gargantuan size, but by its purple-splotched, hairy stems. “Cow parsnip stems have a more ‘furry’ look to them, whereas the hogweed has long, white hairs which are most pronounced at the base of the leaf petiole (stem). But the foliage of cow parsnips and giant hogweeds before they send up flower stalks is so similar it’s almost impossible to tell them apart.”

 

Giant hogweed prefers rich, moist disturbed soils and will establish readily in home gardens. But unlike many invasive plants, giant hogweed doesn’t spread rapidly unless it grows near water bodies: “Hogweed is a particular threat in riparian areas,” says Tasker. “The seedheads fall into the water and spread downstream, where they readily sprout and take root wherever they wash up.”

 

Gardeners “the worst offenders”

“Garden club members can be the worst offenders spreading giant hogweed,” Tasker says. “It’s so spectacular that they pass the seeds along to fellow gardeners.”

 

Even professionals fall for the majestic plants. Tasker says he’s spent time removing hogweed seedheads from the grounds of several foreign embassies in Washington . “The State Department hired a landscape architect who loves the plant,” says Tasker. “He got a bit huffy when he was informed it was on the Federal noxious weed list and would have to be removed.”

 

Have you seen the giant hogweed?

People who suspect they might have seen giant hogweed should call Cooperative Extension’s Family, Home & Garden Education Center’s Info Line, 1-877-398-4769, Monday-Friday, 9 AM -2 PM, prepared to describe the plant and its location. People who have already made a positive identification should notify Doug Cygan of the NHDAMF at 271-3488. Cygan suggests that people not touch the plant while trying to identify it and await a state inspector before deciding on a control strategy.

For more information

• Giant Hogweed and Look-a-Likes
  This Penn State photo-fact sheet will help you distinguish between giant hogweed and its close relatives.
• USDA Giant Hogweed Fact Sheet
• USDA Giant Hogweed Poster
• Fact sheet from King County, Washington
• Hogweed sap burn
  A graphic photo—not for the squeamish.
• Images of giant hogweed
• Lyrics to Genesis’ 1971 recording of The Return of the Giant Hogweed
  A cult classic and testament to the near-mythic status of giant hogweed in Great Britain , where the plant has flourished and spread for more than 100 years.

 

For clinicians

These links may offer useful information for New Hampshire healthcare providers.

• Photodermatitis from Giant Hogweed
  An epidemiological publication of the Oregon Department of Human Services
• Vegetation, Vegetables, Vesicles: Plants and Skin
  From a British nursing journal. Look for information about giant hogweed under the heading Phytophototoxicity.