Russian Knapweed

Description

Russian knapweed was introduced to North America from Asia. It is a perennial that reproduces by roots, rhizomes, and seeds. It can grow up to 1 metre tall and young stems are covered with soft, short, grey hairs. The flowers are urn-shaped and pink to purple in colour, they occur singly at the ends of stems. The bracts underneath the flowers are green with papery edges. Flowers become straw-coloured at maturity.

Type

Perennial

Habitat & Impacts

Russian knapweed thrives in any soil but does very well in clay. It is not tolerant of shade, drought or wet sites. It can invade rangelands and pastures, reducing carrying capacities and yields. Russian knapweed contains toxic compounds that cause a neurological disorder in horses if they consume large quantities.

Method of Spread

Russian knapweed reproduces primarily through seed; however, it can re-grow from root and crown fragments. Seeds germinate throughout the growing season and plants typically flower from May to July. Seed is spread via humans, wind, and animals and can remain viable in the soil for several years.

Location

Found in the south Cariboo and is prevalent in southern BC.

Mechanical

Removal of the plant to ground level prevents seed production and repetition can help exhaust root reserves.

Chemical

Picloram, dicamba, or a combination of clopyralid and 2,4-D are a few of the herbicides that effectively control Russian knapweed. (Ministry of Agriculture, Lands, and Fisheries, 2002).

Biological

There is a gall-forming nematode and a rust fungus introduced in Alberta for biocontrol; these biocontrol's have been introduced into BC but have not established.

CCCIPC Priority & Treatment Strategy

Priority 1 (new invader).

Local Level

Frequently mowing and hand pulling small infestations.

Landscape Level

Chemical control and possible biological control for larger infestations.