Donkey Rhubarb is a threat.

THE most invasive plant in Britain is threatening to smother the
island. Japanese knotweed, or donkey rhubarb, was introduced to Britain
from the Far East as an ornamental plant in 1825. It is currently found
on more than 100 sites in Guernsey and is spreading quickly.
‘It can grow from just a single node and if someone cuts it and
doesn’t dispose of it properly it grows again,’ said States
agricultural and environment advisor Andrew Casebow.
The plant has enormously strong and deep roots which can penetrate
concrete and go through walls. Japanese knotweed is not listed on the
noxious weed ordinance as it flowers but does not re-seed. Mr Casebow
said that the weed could be killed by cutting it back and injecting
liquid into the hollow stems.



And i thought i had problems in my garden.

Mr Casebow sounds like the typical 'expert' employed by the States.

According to the Press article, he has been trying to kill the knotweed with a pesticide, he may have a bit more luck if he used a herbicide.