There are multiple closely related knotweed species present in New York State and the Adirondack PRISM: Japanese knotweed, giant knotweed, and Bohemian knotweed. All species are fast-growing, herbaceous perennial shrubs with jointed, hollow stems. The leaves vary in size between each species, but are generally alternate, leathery, and broadly ovate. A cascade of white flowers bloom in August, and dormant reddish-brown stems are visible in winter.
Confirmed observations of Knotweed spp. submitted to the NYS Invasive Species Database. For more information, visit iMapInvasives
Knotweed species are found along forest edges and stream banks, as well as in disturbed and open areas such as roadways.
Threats & Impacts:
Knotweed’s early spring emergence and dense growth give it an edge over native plants, enabling it to take over large areas. Its thick rhizomes can extend horizontally through soils for 60 feet or more.
Knotweed is very difficult to control. A stem injection or foliar treatment with systemic herbicide can be effective. Always read the label to ensure safe and appropriate use of any herbicide. Repeated controls are often necessary.