Japanese Knotweed is controlled in Japan naturally by a combination of fungus and insects. However, in the majority of Europe, there are no natural enemies for Japanese Knotweed and it out competes all native species for light, water and nutrients.
The speed at which Japanese Knotweed has spread throughout Ireland has been extraordinary. The damage it has already caused to commercial and domestic sites is practically unquantifiable and it now occupies a site in every 10km of Ireland and other parts of Europe. In depth studies are currently underway in various parts of the country to estimate the full extent of infestation.
Specific problems caused by Japanese Knotweed are:
- Damage to paving and tarmac / retaining wall structures
- Damage to building foundations /flood defence structures
- Damage to archaeological sites
- Reduction in land values
- Reduction in biodiversity through out-shading native vegetation
- Many insects/wildlife that are dependent on our native plants are lost or in danger
- Restriction of access to riverbanks for anglers, bank inspection and amenity use
- Damage/reduction to fish breeding grounds
- Causes flooding dues to waterway restrictions
More recently in Britain where the plant is readily established and acknowledged as a serious issue, three financial institution have refused to approve mortgages if it was discovered within five km of a property
It’s estimated it is causing an estimated £166 million (€231m) in damage annually in Britain. The cost to the London Olympics to remove Japanese knotweed from the 10 acre Olympic site cost more than £70 million. Closer to home, as in the case of Kenmare hospital, works to remove the plant cost the hospital in excess of €100,000.