Knotweed Treatment Recommendations for Homeowners and Landscapers
Homeowners: Please share this information with your landscaper and create a treatment plan that we believe is the most effective method for controlling Japanese knotweed.
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.
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:
All Habitat Services
2 Tipping Drive
Branford, CT 06405
AllHabitat.com
(203) 245-1212
All Habitat Services is an ecological management firm specializing in aquatic and terrestrial habitat restoration and vegetation management.
Dan Holmes
Holmes Fine Gardening
PO Box 279
Newtown, CT 06470
HolmesFineGardens.com
(203) 270-3331
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.
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:
All Habitat Services
2 Tipping Drive
Branford, CT 06405
AllHabitat.com
(203) 245-1212
All Habitat Services is an ecological management firm specializing in aquatic and terrestrial habitat restoration and vegetation management.
Dan Holmes
Holmes Fine Gardening
PO Box 279
Newtown, CT 06470
HolmesFineGardens.com
(203) 270-3331
