Knotweed spp.
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.
Common Name: Knotweed spp.
Scientific Name: Reynoutria spp.
Native Range: Asia
Background
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.
Habitat
Knotweed species are found along forest edges and stream banks, as well as in disturbed and open areas such as roadways.
NYS Distribution Map
NOTE: If you receive a “sign in” message, click cancel to continue. Confirmed observations of Water chestnut submitted to the NYS Invasive Species Database. For more information, visit iMapInvasives
Identification
Knotweed has hollow, bamboo-like stems that have a distinctly zigzagging appearance. The leaves are heart-shaped and alternate along the stem. A cascade of small white flowers appears in August.
Impact
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.
Prevention and Control
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.
To learn more, check out our Landowners Guide to Knotweed Control.
