Grounds Maintenance and Weed Control

Japanese Knotweed Control - Swansea

Bay Landscapes has a great deal of experience in knotweed control in Swansea and across South Wales.

Japanese Knotweed (Fallopia Japonica var. japonica) is native to Japan, Taiwan and China and was introduced into Europe (Netherlands) as an ornamental plant in 1849, it was first identified growing in the wild in the U.K. in Maesteg (South Wales) in 1886. It has since then spread to the four corners of the British Isles and most of Northern Europe.

There are 4 main types.

Japanese Knotweed (Fallopia japonica var. japonica)

Giant Knotweed (Fallopia sachalinensis) has much larger leaves which are more heart shaped and can grow up to 5 metres.

Fallopia Japonica var. compacta. Similar leaf to var. japonica but only grows up to 1 metre tall.

Fallopian x bohemica . A hybrid of the sachalinensis and japonica varieties, the leaf is larger than japonica and can sometimes have a heart shaped base or a flat base.

There is also Himalayan knotweed (Persicaria wallicii) this variety isn’t as widespread as the others but is on the increase. Not as distinctive as the others, but has very similar flowers. 

Identification:

Light green stemmed with red / pink blotches up to 3-4 metres tall.  Stems are hollow and segmented with nodes where branches grow from.

Once winter die back has occurred the dead, light brown stems can remain upright for several years.

The roots  (rhizomes) are deep rooted (up to 3m ) and spread up to 7m.

The leaves have a pink stalk leading to the flat base of a pale green, shield shaped  leaf.

The flowers are cream coloured and occur in clusters on long stalks at the end of the summer.

The growing season is normally between March / April through to October / November. It has been known to continue living over winter if temperatures remain above freezing.

Why is it such a problem?:

It is very fast growing and spreads through vegetative means (Rhizomes and contaminated soil movement). As little as  0.7 grams of the rhizome is enough to establish a new plant, which equates to a piece about the size of your fingernail.

It also spreads through water courses, where rhizomes will float down stream and come to rest on river banks and grow. It damages buildings, roads and walls.

Flood defences can also be damaged as it out competes native species that would normally grow on river banks. Once the Japanese knotweed has died back in winter there is no vegetation left to knit the soil together and causes erosion during winter floods.

During the last few years, it has become increasingly common for banks and other mortgage lenders to refuse to lend money against a property which has Japanese knotweed growing; also sometimes in adjacent properties. This can sometimes be overcome once an eradication strategy has been implemented and with a confirmation letter and treatment plan. Using herbicide application techniques the eradication process can take up to 5 years to achieve. Instant results can be achieved by removing the contaminated soil, but this method can become prohibitively expensive.

It also reduces biodiversity by blocking out the light source for native species.

The flowers, which are high in nectar attract bees and other pollinating insects and this has a detrimental effect on native species which are not being pollinated as often.

Legislation:

Japanese knotweed (Fallopia japonica), Giant knotweed ( f. sachalinensis) and Hybrid knotweed (f. x bohemica) are all covered by the Wildlife and countryside act 1981, schedule 9, section 14. Where it is an offence to deliberately cause the plant to grow in the wild.

Also the Environmental protection act, Duty of care 1991. All waste material contaminated with Japanese knotweed is controlled waste.

Control:

There are two main types of control.

1. Physical.

Methods include :

Mowing and hand cutting

Grazing by animals

Digging out / pulling (this method can become financially expensive)

Covering

Barriers and encapsulating (again can be expensive)

2. Chemical methods:

Recommended chemicals:

Glyphosate

2,4-D

Picloram

Aminopyralid / Fluroxypyr

Flazasulfuron

Flumioxazin

Chemical application methods are:
foliar spraying, cutting the stem and filling with herbicide, wiping the leaf with herbicide impregnated weed wipes, stem injection, xylem-mobile herbicides. A combination of physical methods and chemical application can achieve good results if feasible to do so.

There are several trials ongoing around the U.K. at secret locations where a natural predator has been introduced. The Aphalara itadori is a sap sucking psyllid that only lives on Japanese knotweed. This introduction, if successful, would not eradicate the species but merely control it.