Removing moisture could control Japanese knotweed, NUIG study finds

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An NUI Galway study has found that removing moisture could act as a control strategy for smaller infestations of Japanese knotweed.

The study, carried out in collaboration with multinational infrastructure consulting firm AECOM and University of Leeds, shows that incorrect herbicide treatment cannot control the growth and regeneration of this invasive plant.

But fully drying the plant material in a lab environment allowed it to be returned to the soil without risk of regrowth.

The research also showed that if there are no nodes attached to the rhizomes (root like underground shoots), there is no regeneration.

Senior author of the study, Dr Karen Bacon, Lecturer in Plant Ecology, Botany and Plant Sciences, Ryan Institute, NUI Galway, said: “Japanese knotweed is one of the most invasive plant species in the world and has major negative impact on ecology and biodiversity.

“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.

“We also show clearly that the size of the plant fragment is critical to the initial regrowth, with smaller fragments producing much smaller regrown plants. Additionally, if there are no nodes, there is no regeneration, which may suggest potential management strategies in the future.

“This also highlights that small infestations and plants should not be viewed with the same concern as larger ones and that rapid management should be a goal of tackling this problematic species.”

Dr Bacon added: “Our finding that the removal of moisture has a 100% success rate on killing Japanese knotweed plants and preventing regrowth after they were replanted also raises an important potential means of management for smaller infestations that are common in urban environments.

“This requires additional field trials, which we hope to undertake in NUI Galway soon.”