Control

It may be possible to hand rogue or dig up small numbers of plants, although this method is considered marginally effective. Stands should be monitored for several years to guaranty control. This technique should be limited to small juvenile plants growing in sensitive areas where herbicides may not be appropriate. It is necessary to dig up and remove all root stocks and rhizomes, and to burn or bag and remove all plant parts (roots, rhizomes, stems, fruit). Dispose of bagged plant parts in garbage pails, dumpsters, or municipal landfills. In some cases, follow-up spot treatment with herbicide may be necessary for several years.

Chemical control is by application of herbicide to cut stems or foliage. Treated plants may require multiple applications over time, and treated stands should be monitored for several years after the initial herbicide application. The cut stem treatment is used when Japanese knotweed is found growing among desirable, non-target species. Remove stems approximately 2 to 4 inches above ground and immediately apply 25 percent glyphosate or triclopyr plus water to the cut surface. Use an approved formulation of glyphosate in riparian and wetland areas. Always follow label instructions. Bag and dispose of cut stems as previously described.

For individual plants or large solid stands of Japanese knotweed, apply 2 percent glyphosate or triclopyr plus water until the foliage is thoroughly wet but not dripping. Use non-ionic surfactants, fertilizer, and other herbicide enhancing products as recommended and needed. In some cases, it may be necessary to precede foliar sprays with cut stem applications for effective control. In all cases, monitor infestation sites for several years and control sprouts and volunteers as necessary. Always follow label instructions.

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Last Modified: 11/14/2007