Russian knapweed

Russian knapweed

Fact Sheet

About

Latin Name: Rhaponticum repens

Origin:  Eurasia

Physical Description: it is a perennial herb from a rhizome. Its stems are branched, covered in fine grey hairs and grow up to 1m tall. Leaves are alternate and oblong to lance shaped. Lower leaves are deeply lobed. Upper leaves are attached directly to the stem with smooth to toothed margins, and become progressively smaller. Flower heads are urn-shaped, and are typically pink to purple. Bracts are green with papery edges. The root system consists of the taproot, horizontal roots, and their vertical extensions. Tap roots reach a depth of 2 m in the first year, and 5-7 m in the second.

Habitat: it is drought tolerant and can be found growing in dry areas with full sun, such as fields, rangeland, orchards, vineyards, roadsides, railways and other disturbed areas. It can also be found in mesic areas, such as riverbanks and irrigation ditches.

Impacts: it produces allelopathic chemicals which can suppress the growth of other plant species enabling it to form monocultures. Infestations reduce yields of desired plants and decrease the production quality of rangelands. It is toxic to horses (causes chewing disease), but livestock are known to usually avoid grazing on it due to its bitter taste.

Reproduction: it reproduces mostly by shoots budding from creeping roots and less often by seed. A single plant can produce about 1200 seeds per year; seeds remain viable for 2 to 3 years. Root fragments as small as 2.5cm in length can develop into a new plant.

Management Options

Mechanical: hand pulling or digging seedlings is effective as long as the entire root system is removed. Multiple mowing passes can suppress populations however it is most effective when followed up by fall herbicide treatment. Cultivation and tilling is not recommended as root fragments can re-sprout after these activities.

Chemical: Several herbicides with the following active ingredients can control Russian knapweed: glyphosate, aminopyralid, clopyralid, picloram, chlorsulfuron, metsulfuron. For available products, contact your local agri-supply store. Prior to any herbicide application, read and follow the label instructions.

Biological: None available for general distribution.

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