A plant thought to be 'impossible to kill' can be destroyed, a study has revealed

Invasive Japanese Knotweed, the scourge of homeowners, could be killed off by drying it out which prevents even the tiniest fragment regrowing, according to scientists.

The plant thought to be "impossible to kill" can result in mortgages being refused and chemical treatments, that don't always work, can cost £6,000.

Japanese knotweed can regrow even from half a gram, according to new research, and can grow up to 10cm a day to a height of two to three metres.

If left alone, Japanese knotweed can dominate an area to the exclusion of other plants and can even grow through cracks in concrete.

Researchers in Ireland and Britain have found that pulling the plant up and leaving it to dry out completely could be a better solution than most herbicide treatments.

The study found the smallest initial fragment weight to regenerate and survive was 0.5 grams, but the team also found the larger the fragment the quicker and larger the regeneration.

The Japanese knotweed was subjected to air drying for sitting on a lab bench for 38 days and then replanted in soil, provided with the same nutrients, water and light conditions as the growth phase.

The findings discovered the removal of moisture was a valuable strategy for small to medium scale infestations of Japanese knotweed without resorting to expensive chemical treatments.

Dr Mark Smith, Associate Professor from the University of Leeds’ School of Geography, said: “This study provides evidence that while Japanese knotweed rhizome fragments as small as 0.5 g can regenerate and survive, the growth rates and growth success vary substantially based on the initial size of those fragments.

"Smaller fragments resulted in much smaller regrown plants and may thus be less problematic.

“While herbicide treatment is an important control strategy, it is 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, from the National University of Ireland Galway, said: “The findings of this study 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."

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