University of Leeds scientists discover possible method to control growth of Japanese knotweed

Scientists at the University of Leeds have discovered a possible breakthrough in controlling Japanese knotweed – one of the world’s most invasive plants.

Scientists at the University of Leeds have discovered a possible breakthrough in controlling Japanese knotweed

Experts at the University say that removing moisture from the plant before replanting it can curb its growth and prevent it from spreading.

The study was carried out by researchers at Leeds along with the National University of Ireland Galway (NUI Galway) and infrastructure consulting firm AECOM, finding that fully drying the plant in a laboratory environment can prevent its regeneration when re-planted.

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While research has showed that the wrong use of herbicide treatment does not prevent the knotweed from regrowing and regenerating, the drying process did, scientists said.

The University of Leeds

It also showed that if there are no nodes - the area on the stem where buds are located - attached to the root structures, there would be no regeneration.

Japanese knotweed is recognised by the World Conservation Union as one of the most invasive species due to its rapid growth, resilience to cutting and crowding out of other species.

It has for decades been a nemesis of gardeners and landscape planners, with infestations known to damage walls, buildings and pavements and even impact on house buyers' mortgage applications.

The scientists tested the drying theory at three sites on knotweed plant mass which had proved to be resistant to herbicide treatment.

Japanese knotweed is widely regarded as one of the most invasive and destructive plant species

It worked by taking taking different parts of the plant - namely crowns (underground mass from which stems and shoots emerge) and rhizomes (underground root-like structures) - and trying to regrow them at the sites in Leeds, Huddersfield and Lancashire.

Dr Mark Smith, Associate Professor in water research from the University of Leeds’ School of Geography, said that while herbicide treatment was an important control strategy, it was only effective if done correctly.

"Here we found no significant difference in the size of regrown plants from sites that had undergone two years of herbicide treatment and those with no history of treatment, suggesting that the herbicide treatment had not been applied correctly.”

Dr Karen Bacon, Lecturer in Plant Ecology, Botany and Plant Sciences at NUI Galway, said the findings had “important potential” for developing strategies to control knotweed infestations 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," she 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."

Further trials are expected to be carried out in Ireland to test the method, Dr Bacon said.