Japanese Knotweed
Fallopia japonica
Physical Description
The introduction of Japanese knotweed into the Pacific Northwest may have been from many different sources or populations. Although in nature Japanese knotweed produces male sterile an male fertile plants, research suggests that many infestations in the Pacific Northwest are a clonal lineage which have male sterile flowers halting any viable seed production between plants. Regardless, the vegetative reproductive capacity of Japanese knotweed is no small threat and poses the greatest problem. In the presence of Giant knotweed pollen the resulting offspring produces a vigorous, fertile hybrid species called bohemian knotweed (Fallopia x boehemica). There are suggestions that a large percentage of the Japanese knotweed in the Pacific Northwest is actually the bohemian hybrid. The level of viable seed production as a major source of spread is not clear.
- Round to square shaped leaf with a distinct pointy tip and flat leaf base (4-7 inches long)
- Hollow stems or canes have dense red to brown spotting, 5-10 ft tall
- Stems or canes are segmented like bamboo, with red papery sheaths between stem sections
- No true hairs on leaves
- Middle leaf vein square in cross section
- Cream colored, sweet smelling, linear flower bunches at each leaf
- Typically male sterile plants (don't produce pollen)
Where is it located in Lincoln County?
Japanese knotweed is the most abundant knotweed species in Lincoln County. Japanese knotweed is found in every watershed in Lincoln County with the Yachats River harboring the largest single infestation in Lincoln County (greater than 90,000 square ft!) - see photos above.
Control Efforts
This species lives up to its name as one of the worst invasive species in the world. It is highly tenacious, and very difficult to eradicate, even with herbicides. Years of follow up monitoring must be done following herbicide application to ensure that dormant rhizomes do not resprout.
In England, Japanese knotweed is considered a controlled waste and by law must be completely excavated from the soil before a property may be developed, often at a very high cost.
Japanese knotweed is the most abundant knotweed species in Lincoln County. Japanese knotweed is found in every watershed in Lincoln County with the Yachats River harboring the largest single infestation in Lincoln County (greater than 90,000 square ft!) - see photos above.
Control Efforts
This species lives up to its name as one of the worst invasive species in the world. It is highly tenacious, and very difficult to eradicate, even with herbicides. Years of follow up monitoring must be done following herbicide application to ensure that dormant rhizomes do not resprout.
In England, Japanese knotweed is considered a controlled waste and by law must be completely excavated from the soil before a property may be developed, often at a very high cost.
