Himalayan Knotweed
Polygonum polystachum
Physical Description
Himalayan knotweed is different than Japanese and Giant. First, the leaf shape resembles an elongate spear. Himalayan knotweed has relatively thin stems that resemble bamboo stems, similar to Japanese or giant knotweed, but tend to grow continuously along the ground much like lawn grass whereas giant or Japanese often tend to form bunches like shrubs (there are many exceptions to this). This growth pattern and Himalayan's thinner stems typically result in a higher density of stems per square foot than Japanese or giant knotweed. Walking through Himalayan infestations is often difficult.
Himalayan knotweed is different than Japanese and Giant. First, the leaf shape resembles an elongate spear. Himalayan knotweed has relatively thin stems that resemble bamboo stems, similar to Japanese or giant knotweed, but tend to grow continuously along the ground much like lawn grass whereas giant or Japanese often tend to form bunches like shrubs (there are many exceptions to this). This growth pattern and Himalayan's thinner stems typically result in a higher density of stems per square foot than Japanese or giant knotweed. Walking through Himalayan infestations is often difficult.
- Lanceolate or spear shaped leaf, with pointy tip (7-12 inches long)
- Light green, thin, segmented stems 6-10 ft tall
- Green to reddish papery sheaths between stem sections
- Very high density of stems per square foot
- Mostly solid stems or with vary narrow hollow inside
- Cream colored, sweet smelling, flower bunches seen mostly at top of stems
Where is it located in Lincoln County?
Himalayan knotweed is the least abundant in Lincoln County, but appears to be spreading at a quicker rate than Japanese and Giant knotweed. This species tend to be found more readily in urban areas such as Lincoln City and Yachats, which together have the greatest number of infestations. Although found in urban areas it also threatens riparian areas throughout the County.
Control Efforts
Fortunately, this species responds very well to herbicide treatment, with often a single years treatment leading to eradication or greater than 90% control.
Himalayan knotweed is the least abundant in Lincoln County, but appears to be spreading at a quicker rate than Japanese and Giant knotweed. This species tend to be found more readily in urban areas such as Lincoln City and Yachats, which together have the greatest number of infestations. Although found in urban areas it also threatens riparian areas throughout the County.
Control Efforts
Fortunately, this species responds very well to herbicide treatment, with often a single years treatment leading to eradication or greater than 90% control.
