Japanese knotwood removal - Ask Extension
How does MSU extension recommend removing jap.knotwood? Property has small creek at bottom of hill where the knotwood has expanded from a neighboring...
Knowledgebase
Japanese knotwood removal #875831
Asked July 03, 2024, 2:41 PM EDT
How does MSU extension recommend removing jap.knotwood? Property has small creek at bottom of hill where the knotwood has expanded from a neighboring yard.
Ottawa County Michigan
Expert Response
Below is a write-up that I have for Japanese knotweed. After checking that out, please let me know if you have any additional questions. I am happy to help.
Japanese knotweed (Fallopia japonica) is an aggressive perennial that reproduces both by rhizomes (underground stems) and by seed. It is often found in shaded to partially shaded habitats on moist, nutrient-rich soils, though it can thrive in gardens and on roadsides as well.
Physical control.
Repeated chopping or digging may eventually deplete underground reserves thus reducing the competitive edge of Japanese knotweed, however it is expected to take several growing seasons to achieve eradication. Both root and stem fragments can root and result in new plants, therefore any plant material removed for control should be placed in the trash headed to the landfill and not in yard waste or compost. Mowing is not recommended as it can spread the infestation. Mulching with most materials is not an effective means of suppressing Japanese knotweed. However, smothering it for several years with a thick plastic has been shown to be effective. Again, the practicality of this will depend on how large the area is, but you can read some detailed instructions from New Hampshire's Dept. of Agriculture at https://www.agriculture.nh.gov/publications-forms/documents/japanese-knotweed-control.pdf
Biological control.
At MSU Dr. Marianna Szucs laboratory group is working on a testing a biological control agent for Japanese knotweed, however this is still in the preliminary stages of testing for the state. More information Dr. Szucs program can be found at http://mariannaszucs.weebly.com/ in the Resources section.
Chemical control.
Repeated herbicide applications of glyphosate or various brush killers, such as triclopyr (Garlon, Pathfinder, Brush-B-Gon) or triclopyr + 2,4-D (Crossbow) should help keep this plant under control, but eradication is difficult. Chemical applications can be made to cut stems for more effective treatment of small populations, see herbicide labels for details. Glyphosate (e.g. Roundup Weed and Grass Killer Super Concentrate, though there are other generics available at stores like Tractor Supply Company, TSC) is usually the best choice for residential users because of its ease of application and lack of residual activity in the soil, however, in a lawn triclopyr or triclopyr + 2,4-D are better options because they will not harm the grass. Be sure to read and follow all labeled instructions. Repeat applications will likely be necessary. Also note that while these herbicides can be applied anytime the plants are actively growing, early fall applications (when temperatures are still above 50F) are often the best time to target herbaceous perennial weeds, like Japanese knotweed. During the fall, herbicides move to the root/rhizome system with the natural fall movement of carbohydrates to those systems at the time.
If you will be applying herbicides that will enter the water then there is a special list we would need to consult. Please let me know and I can get you more information.
There are more potent herbicides available that may provide eradication, but they are very persistent and can impact trees and shrubs with roots in the area. If you would like more information on these herbicides please contact me via email at <personal data hidden>.
**Note, if your neighbors also have this weed and they are not actively controlling it; it will continue to be a problem. I have seen that in my own yard.
Cooperative Invasive Species Management Areas (CISMAS).
In Michigan there are several groups working to eradicate invasive plant species. Each group covers a cluster of counties and is funded by varying sources, some volunteer efforts, and sometimes property owners themselves. Groups have varying priority species and their abilities to help vary. If they are not able to help with a particular species of interest they still may be able to point you toward local, reputable companies that can help. You can find your CISMA at this site: https://www.michigan.gov/invasives/take-action/local-resources Usually there is a coordinators email and phone number listed and sometimes there is also a web address (or you can do an internet search for the group’s name).
Japanese knotweed (Fallopia japonica) is an aggressive perennial that reproduces both by rhizomes (underground stems) and by seed. It is often found in shaded to partially shaded habitats on moist, nutrient-rich soils, though it can thrive in gardens and on roadsides as well.
Physical control.
Repeated chopping or digging may eventually deplete underground reserves thus reducing the competitive edge of Japanese knotweed, however it is expected to take several growing seasons to achieve eradication. Both root and stem fragments can root and result in new plants, therefore any plant material removed for control should be placed in the trash headed to the landfill and not in yard waste or compost. Mowing is not recommended as it can spread the infestation. Mulching with most materials is not an effective means of suppressing Japanese knotweed. However, smothering it for several years with a thick plastic has been shown to be effective. Again, the practicality of this will depend on how large the area is, but you can read some detailed instructions from New Hampshire's Dept. of Agriculture at https://www.agriculture.nh.gov/publications-forms/documents/japanese-knotweed-control.pdf
Biological control.
At MSU Dr. Marianna Szucs laboratory group is working on a testing a biological control agent for Japanese knotweed, however this is still in the preliminary stages of testing for the state. More information Dr. Szucs program can be found at http://mariannaszucs.weebly.com/ in the Resources section.
Chemical control.
Repeated herbicide applications of glyphosate or various brush killers, such as triclopyr (Garlon, Pathfinder, Brush-B-Gon) or triclopyr + 2,4-D (Crossbow) should help keep this plant under control, but eradication is difficult. Chemical applications can be made to cut stems for more effective treatment of small populations, see herbicide labels for details. Glyphosate (e.g. Roundup Weed and Grass Killer Super Concentrate, though there are other generics available at stores like Tractor Supply Company, TSC) is usually the best choice for residential users because of its ease of application and lack of residual activity in the soil, however, in a lawn triclopyr or triclopyr + 2,4-D are better options because they will not harm the grass. Be sure to read and follow all labeled instructions. Repeat applications will likely be necessary. Also note that while these herbicides can be applied anytime the plants are actively growing, early fall applications (when temperatures are still above 50F) are often the best time to target herbaceous perennial weeds, like Japanese knotweed. During the fall, herbicides move to the root/rhizome system with the natural fall movement of carbohydrates to those systems at the time.
If you will be applying herbicides that will enter the water then there is a special list we would need to consult. Please let me know and I can get you more information.
There are more potent herbicides available that may provide eradication, but they are very persistent and can impact trees and shrubs with roots in the area. If you would like more information on these herbicides please contact me via email at <personal data hidden>.
**Note, if your neighbors also have this weed and they are not actively controlling it; it will continue to be a problem. I have seen that in my own yard.
Cooperative Invasive Species Management Areas (CISMAS).
In Michigan there are several groups working to eradicate invasive plant species. Each group covers a cluster of counties and is funded by varying sources, some volunteer efforts, and sometimes property owners themselves. Groups have varying priority species and their abilities to help vary. If they are not able to help with a particular species of interest they still may be able to point you toward local, reputable companies that can help. You can find your CISMA at this site: https://www.michigan.gov/invasives/take-action/local-resources Usually there is a coordinators email and phone number listed and sometimes there is also a web address (or you can do an internet search for the group’s name).
