Sunday, 17 April 2011

As weeds go, this is the biggest thug of them all

On the common land adjoining our garden we have a beautiful valley, with a stream running through it and a wood. Amongst the trees though is Japanese Knotweed, it can be difficult to get at on the steep slopes of the valley but get at it I do.

We are on our annual hunt of this voracious plant. Before we moved I didn’t know what it was, I sure do now.

Once established, it tends to shade out native plants by producing a dense canopy of leaves early in the growing season and germination of our native plants is further compounded by the thick mulch of decaying canes and slow decomposing leaves left by the Knotweed in the winter. Although Japanese Knotweed is non toxic (edible even - it tastes like mild rhubarb apparently), it offers a poor environment for native insects, birds and animals.

Japanese Knotweed was first introduced to the UK as an ornamental plant by the Victorians. The problem is that it grows unbelievably quickly and it’s a highly invasive species. Currently Knotweed is listed on Schedule 9 of the Wildlife and Countryside Act 1981. This makes it an offense to either plant or cause (or encourage) the plant to grow in the wild. However, there is no obligation to report or remove it if it is growing on your land, but it really is wise to do so; if you see anything like the below appearing – kill it instantly-ish.

Kill it - instantly-ish...
When it comes to removing Knotweed though, it isn't easy. Japanese Knotweed is known for its ability to re-sprout from very, very small pieces of plant and its roots can reach 7 metres horizontally and 3 metres deep making it difficult to remove by digging out.  The majority, if not all plants outside Japan are female so it doesn't have viable seeds here in the UK.  Knotweed spreads either by its own encroaching growth(rhizomes grow rapidly underground) or by regenerating from pieces of the plant or root system that are cut and transported by people or by water.  As we definitley don't want to spread it this makes cutting back and digging out too hazardous for us with such an established problem in a difficult to access area. 

One of the most effective methods of eradicating Japanese Knotweed is with the use of herbicides. For the best results apply just before the Knotweed's flowering, which generally occurs in late summer or early autumn. We use Glyphosate, we use it whenever we see a plant with enough leaves unfurled to make spraying viable we are so paranoid; also it can be very difficult to spray the plants when they are taller than you. This chemical penetrates the whole plant, including the root network.

We have been spraying since we moved here three and a half years ago and although it is obviously still with us the Knotweed has certainly been retreating and is nowhere near as prolific as it once was.  Knotweed can lay dormant for 20 years so our vigil will have to remain in place for many more years to come.

There is a trial at the moment involving an insect that feeds on the sap of the Knotweed plant stunting its growth – but this may or may not work, and even if it does it could be ten years before it reaches us.

Doing nothing is not an option.

As tall as I am - in just this growing season.


Preseli Mags said...

We removed it from the garden by pulling it all up. It eventually gave up. For the huge patches on the farm we have had permission from the Soil Association to spray and find that the best time is just as it is about to die back for the year so it takes the glyphosate down to the roots with it (we've even poured it down the hollow stems).

As you say it starts to retreat... but we've been battling it here for 26 years now. I don't think we'll ever by without the vile stuff! Bring on the Knotweed-killing insects!

the veg artist said...

I read somewhere the other day that a house vendor now has to declare if there is Japanese Knotweed on the property!!!

Lins' lleisio said...

Oh dear, I think unfortunately there is not six clear square miles in the UK which is not affected by this weed, so a lot of people selling will be having to declare they have Japanese Knotweed :(

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