Knotweed

Japanese Knotweed is an herbaceous perennial that can be more readily seen during mid-summer and early autumn. This shrub-like plant develops large dense clumps that are between 3’ – 9’ high. Knotweed can reproduce by seed and by rhizomes that reach up to 15’-18’.


Knotweed Foliage:
The leaves of the knotweed alternate on the stem and produce a knotweed zigzag pattern. They are broadly oval pointing at the tip and are around 6” long and 3” – 4” wide. The leaves vary in color from dark red new leaves (0.4” - 1.5” long) to green with rolled back dark red veins on the young leaves. Mature leaves are heart-shaped green leaves are flattened at the base and usually about 4.7” long.


Knotweed Flowers:
Knotweed flowers that emerge by late summer are creamy-white, about 0.2” wide, and show up in lengthy cluster/spike formations. The spikes are about 3.9” long.


Knotweed Roots:
Over the winter months, Japanese Knotweed spread primarily from underground rhizomes that lie dormant but alive. Often spreading around 3.3’ outwards from the visible stems that are above ground, rhizomes can spread to a depth of more than 3.3’. Therefore, it is easy to fragment pieces of rhizome without realizing it and spread them by disturbing the soil that is several feet away from where the stems are visible.


Treatment for Knotweed:
In order to control the spread of Japanese Knotweed, it is important to target the massive underground root system. Mowing along with herbicide applications can be important for better results. Mowing alone will not eradicate Japanese knotweed because of the large root system. Treatments that can be very effective are foliar, stem injection, and cut-stem applications of herbicides that translocate their active ingredients directly into the rhizome system. Follow-up treatments and monitoring will be needed for between four to ten years (depending on the size/age of the knotweed) in order to eradicate the knotweed population.


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