An urgent call: Protect the river from knotweed

CORNWALL — Control or prevention of the spread of the invasive Japanese knotweed, which is abundant in many area towns, drew discussion at a meeting of the Housatonic River Commission (HRC) held on Tuesday, Sept. 11. Reporting to the HRC was Tom Zetterstrom, the area’s knotweed network co-ordinator and an expert on invasive non-native plants. 

Knotweed and its potential for spreading is not to be taken lightly. It can be found in 40 of the 48 states. Describing his year of work in mapping infestations of the weed, Zetterstrom said he assembled a “network of paddlers” to survey 42 miles from their canoes and kayaks of the Housatonic River from North Canaan to New Milford, in phases.

“We did not have a strategy, but we had a goal,” he reported. 

Based on data collected along the river, Zetterstrom recommended expanding the survey to tributaries and roadsides. 

“We are still in the feasibility zone of knotweed control,” he said. “Let’s not relinquish this river to a weed.” 

He said the battle will require the co-operation of many constituents. North Canaan is already moving ahead with a control phase. North Canaan Selectman Christian Allyn, who is also an HRC board member and who works with Zetterstrom on area invasive control measures, said that his town has already identified the problem areas and is acting to destroy it and prevent spread.

Soil obtained as “fill material” can contain knotweed and contaminate the area where it is dropped. As little as a 3-inch root segment can take hold; its seeds will do the trick, too. Knotweed is currently in bloom, its white flowers producing millions of seeds. Roots can extend outward for 65 feet, and then produce shoots.

Zetterstrom said his group’s goal is to make the Housatonic River knotweed-free. 

“It’s the most aggressive weed I’ve ever seen,” he added. 

Half of the spread can be attributed to human activity, such as using contaminated fill. The Farmington River banks are totally overrun with the weed, he said.

HRC Chair Bill Tingley suggested that if people are bringing in fill contaminated with knotweed, they should be held responsible. New Hampshire state law prohibits the transportation of fill containing knotweed, another board member noted, suggesting that data should be collected at all of the area town landfills. In addition, area town crews need to be educated in identifying and eradicating.

The most effective weapon against knotweed has proven to be Roundup Pro or its active ingredient, glyphosate.

“Early detection and rapid response are key to combating the problem,” Zetterstrom said.