Lee Bergquist

Milwaukee Journal Sentinel

A showy new invasive plant with toxic sap that can burn the skin and grow to a height of 15 to 20 feet has been positively identified for the first time in southeastern Wisconsin.

Hundreds of plants known as giant hogweed were confirmed in Sheboygan in early June, according to the Department of Natural Resources.

Aside from the plant's size — the leaves alone can grow to 3 feet — and ability to crowd out native species, giant hogweed also poses potential health dangers.

According to Michigan State University, the plant's sap contains glucosides that react with ultraviolet rays of the sun and can severely burn the skin, cause blisters or cause temporary blindness.

Hundreds of the plants were sprayed with an herbicide on several properties in a neighborhood on the south side of Sheboygan last week — a "rapid response" effort organized by the Southeastern Wisconsin Invasive Species Consortium Inc. (Small plants can be dug by hand, but people must wear protective clothing because of the sap, according to the DNR.)

"It's a big deal, from my perspective, because it's a prohibited species that's not yet widespread," said Kelly Kearns, a conservation biologist with the DNR. "When we find the plant, we try to get it under control."

The good news in Wisconsin, Kearns said, is that authorities think they have been able to control all known populations.

The plant's discovery in Sheboygan is the closest it's been found to metropolitan Milwaukee.

A native of the Caucasus region of Eurasia, between the Black and Caspian seas, it was bought to the United Kingdom and then in 1917 to the United States as an ornamental plant. Giant hogweed is found in states with similar climate zones: Michigan, Illinois, Maine, New York, Pennsylvania, Oregon and Washington.

Fast-growing, the plant invades roadsides, the edges of woods and empty lots. It prefers shade, especially along the banks of streams, where it can lead to soil erosion.

Giant hogweed was first recorded in Wisconsin in 2004, Kearns said. There have been confirmed reports in Iron County, in far northern Wisconsin, Waupaca County and Manitowoc County.

A single plant produces thousands of seeds, which can be dispersed by flowing water or animals. The most common way the plant invades new territories, however, is humans who are attracted by its size and sheer novelty.

"These are probably the most amazing plant you will ever see," said Jennifer Grenz, coordinator of the Invasive Species Council of Greater Vancouver, Canada, in a YouTube video, where she is dwarfed by plants in their flowering stage.

Said Kearns: "Some people think the plant is really cool and they decide to plant it."

However, regulators take a dim view of the plant, which is sometimes called giant cow parsley. It is listed as a prohibited species, which means the plant is not widespread and is found only in small stands in isolated spots, but is likely to spread if not controlled.

If necessary, the DNR can obtain a court order to inspect and eradicate prohibited species. But in Sheboygan, the homeowner supported the spraying.

Giant hogweed can be mistaken for a pair of native plants, angelica and cow parsnips. Natural resource agencies have posted online videos to show the differences between them.

Last week, a control crew from Brodhead-based Applied Ecological Servicessurveyed the Sheboygan neighborhood and sprayed more than 800 plants with an herbicide, according to Scott Horzen, a board member of the Southeastern Wisconsin Invasive Species Consortium, which helped to oversee the eradication plan.

Neighbors say the plants may have been present for as long as 10 years, Horzen said.

He was present for the spraying. He described the plants as "ginormous — it stands out in a spot because it's so big," he said. "It's unlike any other plant in Wisconsin."