Homeowners: Please share this information with your landscaper to create a treatment plan that we believe is the most effective method for controlling Japanese knotweed.
Late summer through early fall is prime time for managing Japanese knotweed with herbicide.
If you've followed us for a while, you know that cutting knotweed is not recommended and will make things worse. To assist Newtown residents who have begun the herbicide treatment protocol, Newtown Knotweed Initiative is making signage like this one available to homeowners who wish to alert town mowers not to mow their knotweed site. To request a sign, email a photo of your knotweed to [email protected]. If you think you may have knotweed on your property abutting the road and would like to treat it but aren't 100% sure that what you have is knotweed, you can email us to request a site check. Please provide your address and an NKI member(s) will visit your address to positively ID your suspected knotweed. Please do not request a sign if you don't plan to treat your knotweed infestation with herbicide in the September to October window, or if you are but your knotweed is not fronting the road. These signs were specifically created to alert Newtown DPW mowers to the presence of knotweed so that it is is not inadvertently mowed. Thank you for your cooperation. |
Due to knotweed's aggressive nature and ability to easily reroot, NKI does not recommend mowing or digging as a containment measure. Mowing also creates the risk of inadvertently spreading infestations via small bits of knotweed stems or roots caught in mower blades. For this reason, we recommend foliar herbicide treatment.
FOLIAR HERBICIDE TREATMENT WHAT Glyphosate is the herbicide of choice when spraying knotweed. Effective knotweed control is a multi-year endeavor, with repeat sprayings needed once a year for at least three years. Glyphosate has no soil activity. WHEN When using the recommended herbicide described below, timing is key. The best results are achieved with minimal negative impact on pollinating insects when spraying is delayed until after knotweed blooms, typically from September through October. This is also the time when carbohydrates start flowing back down to the root system as the plant prepares to overwinter, making treatment at this time most effective due to glyphosate’s entry into the rhizomes (root system). Do not spray after the first frost occurs or once the leaves look wilted and brown; the opportunity to treat must wait until next fall when the herbicide can be introduced to the roots. |
HOW
Property owners have two options for spraying: • Hire a professional (preferred) Property owners may hire a licensed applicator who can apply two treatments of imazapyr; alternatively, the applicator can do a single application of glyphosate (in a concentration of at least 41%, diluted down to 2-4% with water; read the label for precise guidelines). Repeat applications for at least three more years will be needed (see Notes below), or • Do it yourself The property owner may choose to apply glyphosate themselves within the recommended window using a backpack sprayer or pump. (A commercial applicator's license is required to purchase imazapyr.) Thoroughly apply to all foliage, but not to the point of runoff. Follow label instructions. For more specific tips, we like the guidance here. As a reminder, knotweed should not be cut back unless you plan to treat it with herbicide that season, as cutting it alone will only encourage its growth. Notes: • Glyphosate concentrate must always be diluted. • In each case, foliar spraying should be followed by a wait period of several weeks while the herbicide goes to work, after which the knotweed can be cut down. • Pre-mixed solutions of glyphosate will not contain enough glyphosate to be effective. • It will be necessary to repeat spot applications in (3-5) subsequent years to attack resprouts and prevent re-establishment. Maintenance herbicide applications should follow the same timing (September-October). • Special care must be taken when working near wetlands. In these cases, a wetland-approved herbicide should be used. If you wish to hire a licensed applicator, NKI recommends the following: Michael Switser Connecticut licensed ornamental pesticide supervisor North Country Landscape Management (203) 953-6325 |
