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Key identifying traits
Stout, hollow, reddish-brown, woody stems from 4 to 9 feet tall that
die back at end of growing season forming a heavy mat of dead material
Nodes slightly swollen with thin papery sheaths
Leaves are short petioled, 2 to 6 inches long, about two-thirds as
wide and narrowing to a point
Flower are small, greenish-white to cream, borne in clusters at ends
of stems and in leaf axils
Biology and ecology
- A perennial spreading from long creeping rhizomes, seeds &
stem pieces
- Can form very dense patches, particularly in riparian areas,
excluding most other vegetation
- Introduced from Asia as an ornamental and now found next to
roadsides, streams and ditches and in waste areas and pastures
- Giant knotweed (Polygonum sachalinense) is similar but larger with
leaves about 12 inches long and stems growing over 12 feet tall
Control
Prevention – Learn to
identify plants; know your property and avoid introduction as an
ornamental or as fragments in fill material
Biological – None known at this time
Cultural – Healthy native plant communities help -heavy grazing
keeps both growth and spread in check
Mechanical – Cutting, mowing, fire, digging and covering with
barrier materials have all been used with variable success depending on
scope of infestation and landowner persistence
Chemical – several effective at label rates if used repeatedly
and combined with a revegetation effort-must be careful near water;
refer to the
PNW Weed Management Handbook for specific chemical recommendations |
flowering branch
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