Townwide Knotweed Spraying

Town Wide Knotweed Spraying

The Town of Goffstown will be spraying for Knotweed during the week of October 22, 2018 (weather dependent). 

The Town has hired Lawnboy Landscaping, a licensed applicator, to do the spraying and a special permit for the spraying was granted by the State of New Hampshire. They will be using "Prosecutor" which has been legally registered by the EPA and the State of New Hampshire.

The spraying will occur in areas where new knotweed has been identified and in areas where a re-application is necessary. The following map shows areas of new knotweed, areas for re-spray, and areas where spraying was successful and the knotweed appears to be eradicated. 


Knotweed Map 2018

About Knotweed

Japanese Knotweed is a large, perennial plant classified as an invasive species. Knotweed has hollow stems with distinct raised joints and is sometimes mistaken for bamboo. The plants can grow up to 13 feet tall and leaves range from 2-5 inches long. Knotweed flowers in late summer and early fall. The small flowers are typically cream or white.

Knotweed plants are replacing native plants; covering guardrails, fire hydrants, roads signs; and are interfering with storm water flow in roadside ditches. 

DPW has developed an informational brochure on Knotweed, read more here.  A fact sheet specific to this plant can be found on Department of Agriculture website:


How to Treat Knotweed


Herbicide application is the most effective means of killing knotweed. Spraying of knotweed should be completed at the end of summer/early fall when the plant is large and flowering. Additional treatments should be done approximately every 6 months (spring and fall). 

To view the chemical label for Prosecutor, click HERE


To kill knotweed by the covering method, start by cutting the plant at the base.  Let the leaves and stems dry out before disposing of them or the knotweed will spread. After cutting the plant, cover the areas with a 7-mil thick plastic. Weigh the plastic down with mulch, rocks, soil, etc. The area should remain sealed and covered for 2-5 years. 


Digging or pulling out knotweed can work is small patches, however, it is important to remove as much of the root system as possible. 

Do Not Mow or Weed-whack Knotweed

Mowing, weed-whacking, cutting, and raking are not effective means of removing knotweed and can actually cause the plant to spread. 

If you have any questions, concerns, or would like your house to be removed from the spraying area please call Goffstown DPW at 603-497-3627 ext. 250.