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Derry conservation officials working to knock out knotweed

Union Leader Correspondent

October 01. 2013 9:51PM
The Derry Conservation Commission is tracking the spread of Japanese knotweed. (COURTESY)

DERRY — Conservation Commission members have declared war on Japanese knotweed, a nonnative invasive weed that is sprouting up across town.

Commission members are mapping out where the bamboo-like plant is growing in Derry and using a grid method to chart its progress. Chairwoman Margret Ives updated the members on the ongoing “knotweed attack” during a meeting last week.

“The reason we are after Japanese knotweed is because it grows abundantly; the roots are about 30 to 40 feet and spread,” Ives said. “And we have a lot of it in Derry.”

Japanese knotweed, or Japanese bamboo, first appeared in the area in the early 1800s, Ives said. Japanese knotweed can choke off other native plants, cause soil erosion and even sprout up through concrete and asphalt, according to horticultural experts.

During the fall, the plant has small greenish-white flowers and can be found in Derry at such places as along Island Pond Road and Route 101, Ives said. The best time to control the plant is from July 1 to the first killing frost, she said.

Ives said residents who find the noxious weed should “cut it, bag it and take it to the dump.”

After it is cut, Japanese knotweed shouldn’t be allowed to remain on the lawn. Ives said merely cutting the plant isn’t enough because it can still spread.

“It is important when you cut it to take it off your property,” Ives said. “Don’t dump it anywhere; make sure it goes to the transfer station because they are set to take it.”To prevent the spread and help with eradication, residents are being asked to use Roundup, Ives said. Roundup, which shouldn’t be used near water, is available at Derry Feed, she added.

As part of the campaign to eradicate knotweed, commission member Jim Arruda has worked with IT Director Doug Rathburn to develop a grid map. Residents will then be asked to take a grid or parcel and locate on the map were the knotweed lies. The commission hopes to accomplish its mission of updating the map with the latest location of Japanese knotweed within the next month

“By the end of October, we should get an idea as to where we are standing with the grids,” Ives said.

Residents who want more information on Japanese knotweed can contact Doug Cygan, an invasive species coordinator and entomologist for the New Hampshire Department of Agriculture. Cygan can be reached at

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