This vegetative reproduction can lead to the formation of dense colonies of Japanese knotweed that can out-compete native species. Riverbanks are thus exposed and subject to erosion, yet trees are unable to colonize these areas during the growing season.
Using herbicide is the most effective method of treatment we used a widely used herbicide application used for weed control in aquatic areas. The solution was applied by a licensed herbicide applicator using a backpack sprayer to spray the leaves or injecting the herbicide into the stems of the plants was a method used in more sensitive areas. Manual removal was used when herbicide was not an option. In addition, we surveyed and treated the major known infestations in the Lower Row River, Upper Row River, and Upper Coast Fork River near Cottage Grove.
Approximately 70% of patches identified were treated during this first year of treatment (August 2015). Sites that were left untreated were due to lack of permission from private landowners. 72 knotweed patches at approximately 16 sq ft each and 9 patches at approximately 50 sq ft for a total of 1,602 sq ft in all were treated.