A research study from NUI Galway, in conjunction with multinational infrastructure consulting firm AECOM and University of Leeds, has found that removing moisture could be a potential new method of control for smaller infestations of Japanese knotweed.

It has been proven that incorrect herbicide treatment of the invasive plant cannot control its regrowth, but instead that complete drying of the plant material in a lab environment enabled it to be returned to the soil without risk of regrowth.

Further research also showed that if there were no nodes attached to the rhizomes, there was also no regeneration.

Invasive species

Japanese knotweed (Reynoutria japonica) is widespread in many areas of Europe, North America and the UK.

It grows up to two or three metres in height and can take over the area in which it grows, resulting in the exclusion of other plants.


The study, published in PeerJ on 12 August, investigated the ability of the crowns and rhizomes with varying numbers of nodes to regenerate successfully from three sites in the north of England.

Two sites underwent herbicide treatments for two years prior to sampling, while the third site has no history of herbicide treatment.

It was found that regeneration was linked to plant fragment size and, without nodes, there was no regeneration.

It was also discovered that the removal of moisture on living material ensured 0% regeneration after replanting.

No difference

Results also showed no difference between the regrowth of treated and untreated Japanese knotweed samples, suggesting that herbicide treatments are not always carried out effectively.

Associate director at AECOM and co-author of the study Dr Mark Fennell said: “Our key finding, that drying out the plant effectively kills it, should provide reassurance to landowners that the plant is not as indestructible as is often stated.”