(Associated Press) A Japanese plant brought to America more than a century ago as an ornamental and used for soil stabilization around old mines, railroad beds and elsewhere is taking over parts of western Pennsylvania and elsewhere in the country. While Japanese knotweed didn’t prove very effective at controlling soil erosion, it’s proven very effective at marching along waterways, choking out native plants as it advances.

“It’s basically taken over, especially the streambank areas, and displaced a lot of the native vegetation that should be there,” said Kristin Sewak of the Kiski-Conemaugh River Basin Alliance, a coalition of watershed and conservation groups.

The alliance has been given about a quarter-million dollars from the state and federal governments to fight it, and more money is expected. The alliance plans to take aerial photographs around Johnstown, Pa., to document the plant’s locations, said Sewak, noting that it interferes with rails-to-trails and river access projects.

“It’s really difficult to get to the river in a lot of these areas where knotweed is prolific,” she said.

“What has happened is, it has basically escaped from cultivation and is now growing wild,” said Larry McCormick, a professor of forest resources at Penn State University.

The weed’s height ? it can reach well over 10 feet ? and broad, green, heart-shaped leaves block sunlight from native plants. Once knotweed establishes in an area, “you turn these into monocultures,” McCormick said.

The weed has a massive underground root system that can store lots of food. Along waterways, those rhizomes can break off, float downstream and take root. Knotweed also can release “gobs” of fertile seeds, McCormick said.

“It makes this plant, once established, pretty difficult to eradicate,” he said. Japanese knotweed is strong enough that it can poke through asphalt.

The weed is controlled by using weed killers and frequent cutting. One strategy is to cut it in the spring, at the beginning of the growing season, and again in late summer while dousing it with weed killer.

Jennifer Forman Orth, a University of Massachusetts invasive plant researcher, said highway maintenance crews sometimes unknowingly spread the weed when cutting vegegation because new weeds can grow from parts of stems or rhizomes as small as a centimeter.

Japanese knotweed is in most of the continental U.S. and Alaska, according to the U.S. Department of Agriculture (newsweb sites).

“Once you key in on this plant and know what it looks like, you start seeing it everywhere,” McCormick said.

Japanese knotweed isn’t on either the Pennsylvania or federal noxious weed list. The U.S. Department of Agriculture said the plant is already too pervasive to place on the list. It’s against federal law to grow, sell or distribute noxious plants, which include giant hogweed and mile-a-minute.

Giant hogweed can cause second-degree chemical burns, even blindness. It’s in a handful of states, including Pennsylvania, which has a heavy concentration in Erie County.

While knotweed doesn’t pose a health hazard, Sewak said, “it’s up there” as far as pesky plants.

McCormick says it’s almost as bad as kudzu, another Asian vine that plagues the South.


Like knotweed, kudzu also was thought to be good for erosion control and in the 1930s, the USDA distributed 85 million kudzu seedlings in the South. Later, it discovered that its erosion control properties were limited.