Do you want to control Japanese knotweed mechanically?
Do you have only small patches of Japanese knotweed infestation?
Do you want to control Japanese knotweed by smothering it?
Do you want to control Japanese knotweed chemically?
Do you need to control Japanese knotweed in an area where plants are established within or around non-target plants or where vines have grown into the canopy?
Digging or pulling (uprooting) will eliminate a portion of the root system but not all. Pull the root crown and as much root as possible. Each time new sprouts are seen (look after a week and at least 20 feet from the plant) uproot them and get as much root as possible. This method is only feasible on very small patches. The treatments will need to continue for at least three years but probably much longer depending on the size of the patch.
Covering with heavy plastics and geotextile fabrics have had some success but is costly and requires pulling, cutting, or herbicide treatment near the edges. Cut stems to the ground surface and then cover the stand being sure to extend coverage at least 10 feet beyond the farthest stems. Weigh down the edges and monitor for sprouts.
Hand cutting, mowing, or other methods are not recommended due to the plant's ability to spread from fragments. If this is the only option, be careful not to spread plant pieces and expect to cut multiple times a year for several years. This method is highly ineffective and should only be used if no other options are available.
In areas like these the best method of herbicide treatment is cut stem treatment. Cut the live stem about 2 inches above ground level (between the lowest nodes). Immediately apply a 25% solution of glyphosate or triclopyr and water to the cross-section of the stem. A subsequent foliar application of glyphosate may be required to control new seedlings and re-sprouts. CAUTION: Always read the entire herbicide label. Herbicides are regulated and may only be used under specific conditions. Contact your state department of agriculture for use requirements, restrictions, or recommendations.
From a practical standpoint, the best time to foliar spray is when the plants are 3-6 feet tall. Foliar sprays will require follow-up treatments later in the growing season. Apply a 2% solution of glyphosate or triclopyr and water to thoroughly wet all foliage. Do not apply so heavily that herbicide will drip off leaves. CAUTION: Always read the entire herbicide label. Herbicides are regulated and may only be used under specific conditions. Contact your state department of agriculture for use requirements, restrictions, or recommendations.
Biological controls of knotweed are being studied and not much is known at this time. Also, there is little information about the efficacy of prescribed burns.
Pest Management – Invasive Plant Control, Japanese Knotweed – Polygonum cuspidatum, Conservation Practice Job Sheet NH-595, Natural Resources Conservation Service
https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb1081649.pdf
Sreten null
Hi! I’m Sreten Filipović. I graduated from the Faculty of Agriculture at the University of Belgrade, with a master's degree in Environmental Protection in Agricultural Systems. I’ve worked as a researcher at Finland's Natural Resources Institute (LUKE) on a project aimed at adapting south-western Finland to drought episodes. I founded a consulting agency in the field of environment and agriculture to help farmers who want to implement the principles of sustainability on their farms. I’m also a founding member of the nonprofit organization Ecogenesis from Belgrade whose main goal is non-formal education on the environment and ecology. In my spare time, I like to write blog posts about sustainability, the environment, animal farming, horticulture, and plant protection. I’ve also published several science-fiction short stories.
You can find me on LinkedIn at https://www.linkedin.com/in/sreten-filipovi%C4%87-515aa5158/
