The invasive plant Japanese knotweed is becoming more problematic in the Netherlands and reports of its spread are increasing rapidly, news agency ANP said on Tuesday.

Figures from nature monitoring website Waarneming.nl show the number of reports of knotweed made in the first five months of this year had risen 1.5 times on the same period in 2021, ANP said.

Wageningen University expert Chris van Dijk told ANP the more people reporting that they have spotted the plant, the better, so that action can be taken.

‘It is spread by people, not animals,’ Van Dijk said. ‘If a small part is in soil which is moved from one place to another, then it will shoot up.’ Knotweed grows at speeds of up to 10 centimetres a day.

Knotweed, which can damage building foundations, roads and drains, is extremely difficult to eradicate. Poison injections, electrocution and boiling water have all been tried as remedies but nothing has worked so far.

Last November however, researchers at Leiden University said the Japanese leaf flea, which is a natural enemy of plant, had survived the Dutch winter and could be used to combat it.

Knotweed was introduced to the Netherlands as an ornamental plant in 1823.