Invasive Japanese knotweed

Japanese knotweed is a highly invasive and prolific plant that was intentionally introduced as erosion control in parts of the US many years ago. The very traits that made it seem desirable (extensive roots, reproduction through seeds and root off-shoots, fast growing, easily established on disturbed sites) are now what make it so difficult to remove.

All types of physical control, such as pulling and cutting, are only temporary. Knotweed is posing a serious threat to native plants and their associated natural communities.

The LRAC has joined with other local environmental groups to study truly effective means to control and/or kill Japanese knotweed. Several selected sites have been treated with herbicides approved by the NH Dept. of Environmental Services to test the effectiveness of treatment (percentage knotweed killed) and document unintended negative effects (accidental poisoning or death) to nearby trees. Sites were selected based on landowner input and willingness to participate. Initial treatments are checked and treatments re-applied as necessary. Data from the experiments will be used to create a best-practice method for landowners and professionals who want to remove the plants. Data are also being use to create maps that show where knotweed has become established and how it is moving through the area. To request a report of progress so far, please contact rachel.a.stevens@wildlife.nh.gov .