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14 September 2008

Getting tied up in Knotweed

We have been invaded, but it is almost unnoticed by most of the people it is affecting.
Japanese Knotweed is a bamboo-like plant that can grow to 2-3 metres tall, has broad leaves and spreads, and spreads, ... and spreads. For the record, it is not bamboo and it can be very damaging.

The key problem it poses is that the roots and stalks are very strong, and the large leaves are slow to break down.

Plants push up through pipes, concrete and around flagstones, breaking up the structures on the way and undermining foundations of walls as well as breaking pipes. Above ground, one plant keeps growing and spreading in a way that prevents other native plants from growing by reducing light and creating a layer that stops other seeds from getting established.

Like many other invasive species, such as the Ringnecked Parakeet or the American Bullfrog, it was originally brought it for 'ornamental' reasons, in this case from Japan, without a thought for the potential effect. Now it affects pretty much all parts of the UK.

In Forest Hill, the Japanese Knotweed plant can be found in many places, including in a large mass along the sides of the railway on Stanstead Road. You can also see how invasive it is on the pavements and drives on the corner of Devonshire Rd and Waldram Crescent - where it was potentially responsible for what seemed like a permanent and rather dangerous leak this winter.
This plant spreads vegetatively, in other words it spreads from cuttings of the roots of other plants, and not by seed. It is, in fact, one single female plant that has spread along waterways, railway cuttings and spreading of soil waste.

It takes only the tiniest fragment of root for it to regrow. That makes it very hard to eradicate as it is almost impossible to ensure you remove all root fragments. Treatment with glyphosate on the leaves of young plants has some effect; older plants might require an injection directly into the stem. Nonchemical treatments are being developed, but short of removing, and safely disposing of, many cubic metres of soil from your garden, it is probably not yet possible.

Why should we care? Any invasive species threatens natural habitats and therefore native species. This one also threatens our property. At the moment, the level of our problem here in SE23 is small, but it could potentially get much worse and public awareness is very important.

We must all do our bit to help each other as plants in one garden can easily spread to neighbours' land. We also need to encourage the Council to deal with public areas.

You have been warned!
Read more here: http://bit.ly/japanese_knotweed
Photo from http://www.flickr.com/photos/srcosmo/169318031/

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