Japanese knotweed (Fallopia japonica), sometimes known as Mexican bamboo or Michigan bamboo, is a prohibited species in the state of Michigan. This means that selling, importing, cultivating or transporting this species is not allowed. Mowing and cutting the species should also be avoided as these actions contribute to its spread and may stimulate re-growth. Knotweed can also spread by floating on rivers, streams or lakes.
This species is most easily identified by its stalks that look similar to bamboo and are green to red in color. Japanese knotweed has oval shaped leaves with a pointed tip and a tapered bottom. The flowers grow in long spiked clusters that bloom in August and September.
Japanese knotweed aggressively outcompetes native plants. The plants can grow 3-10 feet tall and limit the light available to the other plants around. They will also release toxic or inhibiting chemicals into the soil to limit the growth of competitor plants.
In addition, it can break through roads and house foundations, causing significant damage. If this species is found growing near a structure, action should be taken to prevent future impacts!
There are multiple treatment options for invasive knotweeds. These include both chemical and non-chemical options.
Non-chemical control methods:
- hand-pulling: Only shallow-rooted (a few inches deep) fragments can be effectively hand pulled and removed. They should be placed in the garbage.
- DO NOT MOW: knotweed can be easily spread by mowing as small fragments can grow into new plants.
Chemical control methods:
- foliar spray: herbicide is sprayed onto the foliage of the plant. This is the most common method used to treat large patches, often done by contractors.
- stem injection: herbicide is injected directly into the hollow stem of the knotweed plant.
- cut and pour: the plant is cut and herbicide is poured into the hollow stem.
Make sure you dispose of any plant material in the garbage, do NOT compost! See our [disposal page] for more information.
A homeowner’s guide to small-scale control of invasive knotweeds [PDF of Guide]
A guide for working with contractors to treat invasive knotweeds [PDF of Guide]