Japanese Knotweed Control Project

Japanese knotweed (Fallopia japonica) is a non-native invasive perennial herb that forms dense colonies that out-compete and displace native species. New colonies frequently arise from plant fragments transported in soil and on soil moving equipment, vehicles, and footwear. Japanese knotweed frequently colonizes stream banks where plant fragments are carried downstream by water, where they come to rest on sand bars and eroded banks and establish new colonies. Japanese knotweed rhizomes can penetrate deep into the soil, making mechanical removal by digging extremely difficult.

Locations

Boston Nature Center (Mattapan), Broad Meadow Brook Wildlife Sanctuary (Worcester), Endicott Wildlife Sanctuary (Wenham), Habitat Education Center (Belmont), Joppa Flats Education Center (Newburyport), Nahant Thicket Wildlife Sanctuary (Nahant), and Rough Meadows Wildlife Sanctuary Rowley).

Project Description

Several methods have been employed to control Japanese knotweed on Mass Audubon wildlife sanctuaries. These have included repeated cutting, mulching, application of herbicide to freshly cut stems, and application of herbicide as a foliar spray.

Repeated cutting and mulching have generally not been found to be effective except for small recently established colonies. Cutting of individual knotweed stems followed by application of herbicide to the freshly cut stems has been generally effective, but is extremely labor intensive and requires follow up treatment in subsequent years.

Cutting of knotweed in late June or early July, followed by the application of a foliar spray of herbicide has been effective in most cases and is an efficient technique for treating large colonies, but follow-up treatment will be needed for several years. 

At the Boston Nature Center, an experimental approach to long-term Japanese knotweed control is underway. This involves an effort to make site conditions less favorable for knotweed growth. Trees and shrubs have been planted in several Japanese knotweed stands to eventually shade the knotweed, making growing conditions less favorable for knotweed. To prevent the planted trees and shrubs from being overwhelmed by the Japanese knotweed, the knotweed is cut by volunteers and staff several times each growing season. It is hoped that the shade produced by the trees and shrubs will eventually reduce the vigor of the Japanese knotweed, which grows much less vigorously under shady conditions.