Townwide Knotweed Spraying

Town-Wide Knotweed Spraying

The Town of Goffstown will be spraying for Knotweed during the week of Monday, October 7th (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 the same areas as the spring spraying. The following map shows areas for re-spray and areas where spraying was successful and the knotweed appears to be eradicated. New areas have been added to the list for Spring 2020 but due to permit constraints, we were not able to get those areas sprayed under our current permit.


Knotweed Map Fall 20191

*Pink lines on the map indicate specific areas to be avoided.


About Knotweed

Japanese Knotweed is a large, perennial plant classified as an invasive species. Knotweed has hollow stems with distinctly 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 the stormwater 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 the Department of Agriculture website:


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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 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 an 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 Sarah Whearty, Town Engineer, Goffstown DPW at 603-497-3627 ext. 250 or email me at This email address is being protected from spambots. You need JavaScript enabled to view it..