Common name: Bohemian knotweed
Scientific name: Polygonum x bohemicum (J. Chrtek & Chrtková) Zika & Jacobson [also Reynoutria x bohemica Chrtek & Chrtková, also Fallopia x bohemica (Chrtek & Chrtková) J.P. Bailey]
Synonyms: Japanese bamboo, Mexican bamboo, Japanese fleece flower
Legal status: Prohibited Control
Life cycle: Perennial
Related species: Japanese knotweed (Polygonum cuspidatum var. compacta Siebold & Zucc.), giant knotweed (Polygonum sachalinense F. Schmidt ex Maxim)
Habitat: Grows in full sun and shade, adaptable to many growing conditions including moist or dry environments and disturbed areas (roadsides, riparian, grassland, forest). Historically used in landscape and foundation plantings, building sites.
Impacts: Environmental: Forms dense stands, outcompetes native plants, alters waterways, facilitates erosion. Infrastructure: Can grow through small cracks in pavement, brickwork, building foundations.
Native range: Bohemian knotweed is a hybrid of giant knotweed and Japanese knotweed that has been documented in Japan. Giant knotweed is native to Japan and Japanese knotweed is native to China, Japan, Korea, and Taiwan.
Background
Knotweeds were introduced to North American in the late 1800s as ornamental garden plants and began to be recognized as problematic in the early 1900s. Giant knotweed hybridizes with Japanese knotweed to form the Bohemian knotweed species. Much of the knotweed present in Minnesota is Bohemian knotweed. In their native range, knotweeds are early colonizers after volcanoes with shoots pushing through volcanic rock. Similarly, shoots can grow through pavement and building foundations necessitating costly removal and repairs.
Identification
Knotweeds are shrub-like, fast-growing herbaceous perennial plants that can grow 10 feet tall. Shoots are hollow and segmented, leaves are arranged alternately and heart-shaped to oval with a pointed tip. Plants form large, dense stands. Rhizomes (underground stems) can spread outwards to 65 feet. New shoots can grow from nodes along the rhizomes. Shoots die back to the ground in the fall after a hard frost and new shoots emerge in the spring. Knotweeds produce lacy clusters of white flowers in late summer.
Management
- Mechanical: Covering (watch for sprouting shoots beyond covering). Mowing during spring or early summer can reduce plant height prior to late summer or early fall herbicide treatment. Mowing stimulates shoot growth and can spread fragments resulting in additional infestations. Bending shoots out of the way can be useful if knotweed blocks pathways.
- Chemical: Herbicide treatments (foliar, cut stump or shoot injection) are the most effective in the late summer or early fall at least two days before frost (see external links).
- Knotweed lifecycle and treatment timing graphic
Images and their description
|
Image Preview |
Caption |
|
|
Comparison of knotweed leaves L-R: Giant, Bohemian, Japanese, Compact Japanese. |
|
|
Bohemian knotweed leaves have a square to heart-shaped base and are up to 12 inches long. |
|
|
Knotweed shoots have segments and are green in summer, turn red after frost, and often remain standing for multiple years. |
|
|
Bohemian knotweed plants are up to 12 feet tall and have multiple branches. |
|
|
Reddish-brown shoots usually remain standing in winter. |
|
|
Clusters of white knotweed flowers bloom in late summer. |
|
|
Small shoots emerge in spring. |
|
|
Knotweed naturalizes in disturbed areas and is often introduced by human activity. |
