JAPANESE KNOTWEED is replacing purple loosestrife as one of the most pervasive invasive species in the state. Knotweed came to the United States from Japan in the 1800s to be used mostly as a landscaping plant. It grows in thick clusters, similar to bamboo, and has no known predators here.

Unlike loosestrife, a pretty but insidious plant that can choke wetlands if left unchecked, there is no known biological means of controlling knotweed. For more than 10 years, the state has been battling loosestrife by shipping in a kind of beetle that eats the plant, weakening it and controlling its spread.

Doug Cygan, invasive species coordinator with the Department of Agriculture, said that plant is now under control, but the calls to his office regarding knotweed are increasing.

So far, Cygan said, there's no good biological means of controlling knotweed. He recommends using herbicide. An alternative is to cut the plants at the base, put them in a black garbage bag, place them in full sun to kill the plants and then compost them. Cygan said digging the plant up is difficult because of its extensive root system.

"Do not mow it," he said.

Mowing along highways has largely contributed to the spread of the plant. Each plant has several hundred nodes, or joints. When the plant is chopped up by a lawnmower, each node can sprout into a new plant. Cygan said the state has stopped mowing areas of knotweed and is removing populations of the plant that occur in areas of road construction.

For more information about controlling knotweed, call Cygan at 271-3488.

CHELSEA CONABOY