Gaining ground in Housatonic River knotweed battle

SHARON — After three years of intensive effort, invasive Japanese knotweed on the banks of the Housatonic River near the historic West Cornwall Covered Bridge on the Sharon side has been defeated and the area reclaimed with native riparian plantings. 

The end of that project was celebrated with speeches and final plantings at the site on Saturday, Oct. 3.

Active in the daunting project were the Housatonic River Commission (HRC) and the Housatonic Valley Association (HVA). One of their goals is to further the possible designation of the Housatonic River as a federal Wild and Scenic waterway. Such a designation would bring potential access to more resources to advance reclamation work; it is also believed that it will help set up protections for the river into the future.

Housatonic River Commission member Jim Saunders was on hand to help park cars on the Sharon side of the river before joining the work detail. His enthusiasm for the work of the volunteers was evident, as was his commitment to achieving the Wild and Scenic status for the river.

About 25 people attended the Oct. 3 riparian planting celebration, a feature of which was a talk by Tom Zetterstrom, a naturalist and invasive species specialist, who reviewed the entire project that began three years ago. Zetterstrom, a native of North Canaan, is also an expert in many trees that are native to the area.

Volunteers planted 50 native plants on Saturday, including swamp white oak, butternut, dogwood, arrowwood, viburnum and prairie willow, according to Mike Jastremski, HVA Watershed Conservation Director and a member of the team.  Jastremski’s son, River, 10, came along to help with planting.

Zetterstrom explained that knotweed is a monoculture non-native infestation that, once established, reduces by 97% the diversity of insects where it occurs. But once an area is restored and flourishes with native plantings, it will promote the welfare of fish, birds and insects.

Such native riparian plantings along riverbanks effectively control erosion and help filter and keep water clean.

The principal cause of the spread of knotweed locally is the removal of topsoil from one location — the topsoil likely to contain bits of knotweed — and the spreading of that contaminated fill to new locations.

Treatment of contaminated fill to remove the bits of knotweed is an initiative now underway in Cornwall.

Zetterstrom recounted how 10 volunteer “paddlers” (enthusiasts of river travel by kayak and canoe) visually surveyed the 84 miles of riverbank from the state’s border with Massachusetts down to New Milford, Conn., mapping serious knotweed infestations — which are large and numerous.

In the Northwest Corner, Zetterstrom’s mapping indicates a total of about 44 spots where knotweed is established, 20 of those on state-controlled land, and 22 along town roads.

To destroy knotweed root systems, which have a biomass that is 60% underground, cutting the plant above ground is useless, Zetterstrom said. Control is through a combination of spraying and stem injections.  The third and final year of the battle is spent in spot treatments.

“We are working to correct the mistakes of the past and not make the same mistakes in the future,” Zetterstrom said. Important to the long-range work are the volunteers who come together and commit to the task of intervention, even seeking coalitions with neighboring towns.

“Residents need to understand what is being done. We need partnerships with the town and the state Department of Energy and Environmental Protection,” said Karen Nelson, a member of the Northwest Conservation District.