Japanese Knotweed

The Municipality of Mille-Isles needs your help to fight the Japanese knotweed. This extremely invasive plant threatens our wetlands and underground infrastructures such as the septic field. This real bamboo-like plant plague is one of the 100 worst nuisance species in the world. A segment as small as one centimeter (1 cm) can generate a new plant and its area increases by 29% each year. It’s easy to imagine how big it can get!

Help us control its spread by declaring its presence on the territory of Mille-Isles at the following address: nbouchard@mille-isles.ca.

Here is some useful information to recognize and counter the Japanese knotweed.

How to identify it?

Japanese knotweed has long hollow stems that look very much like those of bamboo. It spreads as a dense bush, it has alternating leaves and a zigzag twig. At the end of July, its colonies form small white flowers gathered in clusters.

What to do?

Some methods exist to control Japanese knotweed colonies. The choice of method will depend on several factors related to the characteristics of the colony and the environment in which it grows.

However, the most widely used method is the mechanical process which consists of:

  1. Cut the stems flush with the ground with a pruning shears or a pruner;
  2. Place cuttings in leak-proof bags to be left in the landfill site. Japanese knotweed should never be composted or put at the edge of the forest, as it will come back to life;
  3. Install a geomembrane on the invaded area. It is important to put heavy stones or tree trunks all around the membrane to prevent the plant from coming out from the sides. This step is crucial, the goal is to suffocate the plant and its root system. It will be important to keep an eye on the evolution of the eradication;
  4. It is very likely that a cut of the new shoots around the tarp will be necessary every month;
  5. Plan a plantation of native species where you have controlled it to ensure that it does not regrow.

How to reduce its proliferation?

Because its eradication is extremely difficult, here are some tips to follow:

  • Avoid cultivating it;
  • Avoid mowing the lawn, as mowing residues will help disperse it;
  • Do not try to pull it out: its rhizomes are very deep and you risk forgetting fragments in the soil;
  • Inform the people around you of the presence of Japanese knotweed.

Environmental and economic issues

By appropriating all the space and threatening the survival of other species by releasing toxins into the soil, Japanese knotweed limits biological diversity and attacks the integrity and balance of ecosystems.

It has a negative impact on the environment, including wetlands. If this plant is found on a shoreline, its erosion by water could transport segments of the plant and propagate it on all the shores of the lake.

In addition, this plant can cause significant damage to infrastructures such as the septic field or the foundation of a house. Its ferocious roots become as big as a coin and infiltrate up to seven meters (7 m) from the initial plan.