Column: Dangerous giant hogweed found

Published 4:31 pm Thursday, July 19, 2007

By Staff
A pretty much routine affliction I suffer is poison ivy rash. Cutting firewood, gathering wildflower seeds, working on prairies and hunting mushrooms guarantees year round exposure and I can get the stuff just thinking about it.
If the poison ivy should somehow miss me my activities in the swamps with butterfly and habitat work throws me headlong into the closely related poison sumac, for me even nastier than poison ivy. I've always had these rascals at the very top of my dastardly plant list, as bad as green things get. However, my daughter and her husband recently returned from a trip up in central Michigan where a friend showed them a much nastier plant, giant hogweed. Though I haven't yet encountered it, all accounts are that it makes a bout of poison ivy or sumac seem almost pleasurable.
Giant hogweed is very serious stuff. The clear, watery sap from this plant causes severe skin irritation in susceptible people. It's a reaction called photodermatitis. Skin contact with the sap followed by exposure to sunlight causes large painful, burning blisters, open sores and red blotches that later develop into purplish and blackened scars that remain for years. Contact with the eyes can cause temporary or even permanent blindness. Giant hogweed is listed as a federal noxious weed making it illegal to propagate, sell or transport anywhere in the U.S.
The term GIANT hogweed is appropriate for here in Michigan it grows up to 12-feet tall with five-foot wide leaves and flowers up to two and a half feet across. In more southerly, warmer areas it can reach imposing heights of twenty feet. This massive, majestic size and imposing appearance make it attractive in arboretums and gardens which is how it got here in the first place. It's native to Eastern Europe and Western Asia and was introduced into the U.S. in the early 1900s. Like so many alien plant species it is invasive and persistent, easily crowding out other native species. It prefers moist, rich soil and readily establishes in roadside ditches, stream banks and damp, open woods.
Giant hogweed is a stunningly attractive plant. The long, hollow stems are two to four inches in diameter and resemble large bamboo canes. They are green with large purple blotches and covered with coarse white hairs. The huge leaves can be up to five feet across near the bottom of the plant. They have deep, irregular lobes with course, sharply toothed margins. The flowers, which bloom from June through August here in Michigan, are small, white blooms clustered into a large umbel, sort of like huge white broccoli. These umbels are gently rounded on the top, flat across the bottom and can be up to two and a half feet wide.
Cow parsnip is a harmless plant that closely resembles giant hogweed. It grows six to eight feet tall but the leaves are smaller and the flowers are only six to ten inches across. The stems of the cow parsnip are green with perhaps just a slight tinge of purple, lacking the pronounced purple blotches of hogweed. Others mistaken for hogweed are angelica and poison hemlock but their leaves are much smaller and more fern-like and the flowers much smaller.
The U.S.D.A. has been monitoring giant hogweed since 1998 and it is known to occur in 11 states scattered from coast to coast, recently including Michigan. It has been found in 13 Michigan counties. Closest to us are Berrien, Kalamazoo, Branch and Kent counties. The others are randomly scattered throughout the state, including the U.P.
Obviously, if you come across suspected giant hogweed don't mess with it. Watch the kids for the large, hollow stems beg to be employed as blowguns or toy telescopes. It does no good to cut or mow it for it only re-sprouts with gusto. If you should come in contact with the sap wash immediately with lots of soap and water and keep the area covered with sun proof material for a week or so. Remember, it's the sunlight that triggers the reaction. To report suspected giant hogweed call the Giant Hogweed Hotline at 1-800-292-3939 and let them deal with it. Carpe diem.