Japanese knotweed, sometimes called Japanese bamboo, is a fast-spreading perennial that threatens the native plant life of any area that it invades. This weed grows between 3 and 10 feet tall and spreads through underground rhizomes, which are root-like structures, and by seeds. The rhizomes of Japanese knotweed are very difficult to remove if left unchecked, as they have been known to reach up to 30 feet in length. It is important to eradicate Japanese knotweed quickly from your property because it can overtake large areas in a very short time.
Put on a sturdy pair of rubber gloves before beginning. It's also wise to wear pants and a long-sleeved shirt to protect your skin from coming into contact with the chemicals used to remove Japanese knotweed.
Mix the chosen herbicide according to instructions. Add liquid dye to the mixture and shake well. Make sure that you add enough dye to darken the solution substantially so that you will be able to tell which areas have been treated. Label the bottle to avoid confusion as to its contents.
Clip the stem of the Japanese knotweed 2 to 3 inches from the soil using lopping shears. Spray the herbicide on the cut part of the stems as soon as you are finished clipping them. It is very important to do this promptly, as the plant develops a protective seal after being damaged that will prevent the herbicide from being absorbed.
Do not mow or cut the stems for seven days after treatment. This will allow the herbicide to effectively penetrate the roots.
Cut and treat the Japanese knotweed again in early fall.