Officials Look For Solutions To Stop Spread Of Japanese Knotweed

06/01/12 7:34AM By Susan Keese
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AP/Toby Talbot
Japanese knotweed grows on a stream bank in Bethel. The flood waters of Tropical Storm Irene and work to remove silt and restore roads afterward had an unintended consequence: they spread Japanese knotweed, an invasive plant that has already clogged some

Tropical Storm Irene provided a perfect opportunity for invasive plants to multiply on riverbanks that were scoured bare by the flood.

Of special concern is Japanese Knotweed, a fast moving invader whose stalks were already crowding waterways and roadsides.

Knotweed is hard to kill once it's well-established. So this summer, wildlife officials are enlisting the public's help in removing new knotweed plants before they're deeply rooted.

Sylvia Harris walks the road bordering the Rock River in South Newfane.  A new metal guardrail marks the barren, rebuilt bank where dozens of trees and plants were washed away in Tropical Storm Irene.

Harris is a soils specialist for the U.S. Natural Resources Conservation Service. She says the seeds that could re-grow the native vegetation are in the soil.

But they don't stand a chance if Japanese knotweed comes up first.

"Knotweed is going to be one of those things that comes back really quickly and shades out any seedlings or any new growth that's coming up below it," Harris said.

Knotweed has already invaded Vermont. Many roadsides and waterways are lined with impenetrable patches of the tall, hollow, leafy stalks, where nothing else can grow.

Established colonies can take years to destroy. Some people add a few drops of an herbicide to the plants' hollow centers after cutting the stalks. But Harris says the chemicals can harm other species, and still require repeated use. 

"The way that people end up trying to control it mechanically is cut it every month, down to the ground," Harris explains, "and take all these cuttings and put them in a black bag, for a year."

Harris says a two-inch piece from a single knotweed plant, will root and form a whole new colony.  And unlike native species that shade rivers and hold the soil, knotweed's reproductive strategy actually helps cause erosion.

"Because it's made to do that. It's really fragile in that it breaks off, so that it's not going to be supporting the bank. So when the bank washes away in a storm, the knotweed is happy because it gets to go somewhere else," Harris said.

That's why scientists are so worried about the knotweed carried off in last August's floods.

Bob Popp, the state botanist, says the spread of knotweed by the storm could result in an ecological catastrophe.

But Popp says there's also good news: it might be possible to just pull the new plants up before they put down roots and become a worse problem.

"We have reason to believe that newly established populations of knotweed can be controlled mechanically, relatively easily because they don't have an established root or rhizome system," Popp said.

The state has hired a coordinator to study how the plant has spread, and to work with landowners and citizen groups to remove the still un-rooted pieces.

It will take a lot of fingers sifting through a lot of silt. But it may never be easier than it is now.

vtinvasive.org

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