Research could provide new way of controlling invasive Japanese knotweed

12 Aug 2021

Japanese knotweed. Image: Dr Mark Fennell/AECOM

Infestations of Japanese knotweed can be problematic but new research may provide a solution.

A new strategy for addressing a pesky plant has potentially been developed by researchers from NUI Galway in collaboration with infrastructure consulting firm Aecom and the University of Leeds.

Japanese knotweed is an invasive plant found in many areas of Ireland, Europe and the US, particularly in urban settings. The knotweed can reach as tall as three metres and can dominate over other plants, posing a risk to biodiversity in infested areas.

But the new research, published in PeerJ, demonstrated that fully drying out the plant in a lab made it possible to return the weed to soil without risk of regrowth. It also found that without any attached nodes, the plant’s rhizomes – which send out roots and shoots from its nodes – were incapable of regrowth.

Samples of the plant were taken from three sites in Yorkshire and Lancashire in the north of England. Two of the sites had received an application of herbicide prior to the sampling, while the third site was previously untouched.

“Japanese knotweed is one of the most invasive plant species in the world and has major negative impact on ecology and biodiversity,” said senior author of the study, Dr Karen Bacon of NUI Galway.

“The findings of this study that showed virtually no difference between the regrowth of treated and untreated Japanese knotweed samples suggest that herbicide treatment, which is often the most suitable approach to tackle the species, is not always being done effectively.”

Herbicide is a common approach to dealing with these growths but is limited by the plant’s ability to regenerate from small, surviving fragments. The plant needs unaffected rhizomes to regrow, but it was previously unclear how much material was needed for successful regeneration.

‘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’

The research found at least one node was necessary for successful regrowth of rhizomes and the smallest fragment weight to regenerate and survive the experiment was 0.5g. A sample this small would likely only produce a comparably small plant, which would take years to grow and spread. Nevertheless, it demonstrated the plant’s tenacity and ability to survive.

After an experiment monitoring the growth of the different plant samples, some of the fragments were left in the lab for 38 days until all of their moisture had evaporated. They were then replanted and given the same conditions as in the growth portion of the experiment.

The researchers found the plants stayed as they were with no regeneration or regrowth. Researchers said this means the strategy could prove a valuable tool in the arsenal against small and medium Japanese knotweed infestations. As well as killing the plant, it would provide a new option for dealing with the organic material, the removal of which often proves costly.

Dr Mark Fennell, associate director at AECOM and co-author of the study, said: “Our latest research sought to add to existing knowledge about how to manage and remove Japanese knotweed. 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.

“While this invasive species remains a problem plant that can have a negative impact on biodiversity, our research provides a better understanding of the plant, paving the way for the development of more efficient and cost-effective ways of dealing with it. We hope our research helps to challenge some of the popular stigma that surrounds Japanese knotweed.”

Sam Cox was a journalist at Silicon Republic covering sci-tech news