Japanese Knotweed is a beautiful plant when in full, white flower stage. Too bad it is such a thug and invasive. It also makes a nice hedge, but quickly overtakes the properties if used as a boundary plant. Colonies can be seen just about everywhere along roadsides, in meadows and yards as it spreads so freely.
Japanese knotweed is also known as Japanese bamboo, American and Mexican Bamboo due to its hollow stems with nodes on them. The plant is known by three different Latin names of Fallopia japonica and Polygonum cuspidatum Siebold & Zucc. And Reynoutria japonica Houtt, but it all the same plant. No matter what you call it, it is aggressive, invasive and extremely hard to kill once established.
The plant was brought to the United States during the 1890’s from Asia as a solution to erosion. It will grow in just about any situation from full sun to complete shade, rich or lean soils, and dry or soggy soils. It tends to make a colony of plants, out-competing any and all other plants resulting in a monoculture. Since it evolved on another continent, it has no native predators, insect or animal that eats it enough to control its spread.
It reproduces vegetatively. If digging it out, any tiny piece of root left in the ground will quickly send up a shoot to get reestablished. Control measures are difficult. Heavy machinery can dig out large infestations and monitor for a new sprouts to pull or treat with herbicides. Herbicides which contain Glyphosate or Triclopyr are the most successful and should be used before the plants flower or sprayed on cut stems. It has been reported that monthly mowing for five years will finally eradicate a large area.