Experts Say Time Is Running Out To Fight Spread of Japanese Knotweed

May 22, 2013

Invasive plants specialists say time is running out to easily remove Japanese Knotweed spread by Tropical Storm Irene.

Knotweed is an invasive plant that grows in thick patches along Vermont waterways, on roadsides, and in backyards.

The plants develop huge root systems that take years of repeated removal, and often pesticides, to destroy. Pieces break off easily and every fragment can develop into a new knotweed plant.

Vermont botanist Brian Colleran says Tropical Storm Irene spread many new knotweed plants throughout the state.

But Colleran says new plants are much easier to remove than established colonies.

“It’s really easy work to do to prevent long term impact, if you can get right on it. And if you don’t take advantage of this early season window before the root systems have grown too large to effectively remove as a whole piece then you’ve got a problem later on down the line,” Colleran said.

Last summer Colleran traveled the state working with local groups and the Vermont Youth Conservation Corps to remove thousands of new knotweed plants.

Colleran says this year the plants he’s finding near storm debris are much bigger. He says that means the roots are spreading and may soon be impossible to remove by hand. So he’s calling for fast action.

He says new plants are usually isolated and no bigger than waist-high. The root systems are only about four inches deep.

“The simplest way to get into it is to dig slowly and carefully with a very small spade and try to find the whole plant. Many of these plants you can still see the fragment that the flood left behind - it’s darker it’s kind of rotted looking. If you can find that and trace all the rhizomes and runners connected to that, you can pull out the whole plant,” he explained.

Colleran says knotweed emits a chemical that prevents trees and other vegetation from growing. The plants are strong enough to crack concrete and push through roads and foundations.

He says plants should be burned after they’re removed -- never left on the ground or in trash bags.