Invasive Knotweed Discovered at Transfer Station

Be careful how you deal with it

May 22, 2013 • Saved under Committees
By Mary Anne Broshek, Andover Conservation Commission
Japanese Knotweed is a highly invasive plant that's in Andover and must be handled carefully to keep it from spreading. Photo: de.Wikipedia.org/wiki/Benutzer:MdE
Japanese Knotweed is a highly invasive plant that’s in Andover and must be handled carefully to keep it from spreading. Photo: de.Wikipedia.org/wiki/Benutzer:MdE

Japanese Knotweed is found throughout Andover, and it is important that we start controlling it. Japanese Knotweed is an invasive plant in New Hampshire and cannot be tossed in the compost/plant debris pile.

  • Invasive species in the United States are a problem that costs somewhere in the range of $138 billion annually to control.

  • The reason for Japanese Knotweed’s introduction to the United States was that it is an excellent plant to help control erosion, which is why it can be found in dense thickets along roadsides and stream beds.

  • It produces a series of underground, root-like stems called rhizomes that will produce their own roots and eventually form new plants. This same property of the plant makes it extremely difficult to eradicate.

  • The reason why Japanese Knotweed is such a problem is that it has no natural predator. The weed will form dense thickets that will eventually crowd out native plant life and completely change the habitat it has been placed in.

  • Japanese Knotweed can produce asexually from a single fragment of the plant. One node on the stem can produce the shoots and roots of a whole new plant.

According to Doug Cygan at the New Hampshire Department of Agriculture, you must be vigilant. Dig deep around the base of the plant, and try to remove all of the rhizomes running underneath the ground. Place it in a plastic bag (to help prevent its spread) and bring it to the hopper or the burn pile at the Transfer Station. Herbicides can be used, as well, but be careful, and try to use these only as a last resort. As a substitute to herbicides, salt water has been proven to be effective against Japanese Knotweed while having a minimal impact on our environment.

Because these plants are so resistant, using the compost at the Transfer Station can spread the problem, so look carefully where you have used this compost and remove it at first sight.

There are three steps to getting rid of invasive plants: Remove, Destroy, Replant with a native species. The native alternatives for Japanese Knotweed are  Sweet Pepperbush, Maleberry, Silky Dogwood, and Elderberry.

Resources

  • There is a large poster of all of the New Hampshire invasive plants in the recycling building.

  • The UNH Cooperative Extension Web site at plcnh.org/invasivesguide.htm has information on each New Hampshire invasive with color photos, the harm it does, a description of what to look for, how to get rid of it, and what native species can be planted in it place.

  • Andover-specific invasive plant map at Wildlife.state.nh.us/invasives/.

  • Contact an expert: For questions about invasive plant species in New Hampshire, contact douglas.cygan@nullagr.nh.gov.

  • The New Hampshire State Forest Nursery in Boscawen sells native plants, trees and shrubs: NHNursery.com.