Montana: Four noxious weeds to be on the lookout for |

Montana: Four noxious weeds to be on the lookout for

BOZEMAN – Four new Extension publications are available that describe the biology, ecology and management of the noxious weeds: knotweed complex, flowering rush, Scotch broom and yellow starthistle.

These weeds are very limited in their distribution across the state and are Priority 1A and 1B species on the Montana noxious weed list. Preventing further invasion of these species is critical, and starts with learning how to identify them, knowing where they might grow and what to do if and when plants are found. These publications will assist with these important tasks.

The knotweed complex is made up of Japanese knotweed, Giant knotweed, Himalayan knotweed, and Bohemian knotweed (Polygonum spp.) (publication EB0196). They are perennial, rhizomatous plants resembling bamboo with hollow stems and rapid, aggressive growth habits. Native to Asia, they were introduced to the U.S. in the late 1800s, predominantly as ornamentals. Members of the knotweed complex can outcompete existing vegetation to form dense monocultures, and they are difficult to control once established. Management options are discussed in detail in the new publication.

Flowering rush (Butomus umbellatus) (publication EB0201) is a non-native aquatic weed resembling a large sedge that grows along lake shores, slow moving rivers, and wetlands. It was first recorded in Flathead Lake in 1964 and has since spread to reservoirs and river systems in northwestern Montana. Prolific growth along irrigation ditches reduces water availability, and formation of dense stands around shorelines and docks inhibits recreational activities like boating, fishing and swimming. Learn how to identify flowering rush and learn exactly where it is growing in Montana in the new publication.

Scotch broom (Cytisis scoparius L.) (publication EB0202) is a highly invasive perennial shrub. It can be recognized by its bright yellow flowers, clover-like leaves, and shrubby growth habit. This species was introduced to the U.S. in the 1850s to control soil erosion and as a landscape ornamental. Scotch broom is currently limited to a couple counties in northwestern Montana, but is widely distributed in Oregon, Washington, and California.

Yellow starthistle (Centaurea solstitialis) (publication MT201101AG) is an annual forb in the same genus as spotted knapweed. Rosettes resemble dandelions with deeply-lobed leaves. Bright yellow flowers grow singly at the ends of one to five feet tall stems. When in bud, and during or after flowering, this plant is easy to recognize due to spines up to one inch long that protrude from the flower base. Yellow starthistle causes chewing disease in horses, a potentially lethal condition. Learn more about this plant and its threat to horses in the new publication.

These new publications will help Montanans prevent the spread of these noxious weeds by reporting new infestations to their local weed district and properly managing existing infestations. Publications can be downloaded or ordered through MSU Extension publications, online at; by calling 406-994-3272; or by sending an e-mail to

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