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Dr. Dan Jones battles Japanese Knotweed

Welcome to a magnificent five-hectare haven situated on the picturesque banks of the river Taff, just outside Cardiff. Here, a remarkable and audacious experiment has been unfolding for over a decade, revealing the secrets of taming the notorious knotweed. Leading this endeavor is the dedicated and tenacious Dan Jones, who embarked on his knotweed management PhD journey back in 2011 and has since become the caretaker of this peculiar patch.


Jones, of Advanced Invasives consultancy, encounters countless misconceptions and misguided attempts at combating knotweed. He recalls instances of people resorting to pouring boiling water or using salt, unaware that knotweed thrives in salt water and remains unaffected by these methods.


Realizing the value of trials in unraveling effective strategies, Jones sought out a unique location—a deserted sports field next to a historic home. Knotweed had weakened the walls of the abandoned changing rooms and crept dangerously close to the house itself. Fortunately, the generous homeowners allowed Jones to transform their land into a sprawling laboratory.


Looking back at Jones's records from 2012, you'd be confronted with a jaw-dropping sight—an awe-inspiring jungle of towering knotweed, dominating everything in its vicinity. The presence of a single earthworm was the only evidence of life encountered during the installation of more than 200 fence posts to mark the test plots.


During the active growing season, Jones frequents this site, dedicating himself to digging, spraying, and devising his next moves. I had the opportunity to join him on a harsh February day, battling the biting winds and drizzling rain that transformed the ground into a muddy quagmire. Together, we ventured along narrow paths meticulously cleared by Jones. Reflecting on his early days, he reminisced about how, in the summer, he would trim the knotweed along three paths, only to find it towering knee-high again at the starting point by the time he finished.


Within the precisely marked plots, Jones conducted an impressive 19 different experiments, meticulously observing the outcomes. Surprisingly, he discovered that using machinery or brush cutters to mow the knotweed only made matters worse. The process shredded the rhizome into fragments, scattering them across the field where they rooted and thrived. Jones explored various herbicides, even including picloram, once employed as Agent White during the Vietnam War to defoliate jungles. Ultimately, the most promising candidate proved to be glyphosate. Jones experimented with injecting it into the knotweed's stalk, spraying it on the leaves, and even pouring it down sawed-off stems.


In 2018, Jones published his groundbreaking findings, revealing his most successful regimen. His recommended approach involved an annual application of glyphosate, either through spraying or injection, for up to seven years. This paper became the holy grail of knotweed management, offering a way to address and manage the plant rather than completely eradicate it. Admirers of Jones's work, like Santo, express their admiration for the practicality it brings to dealing with knotweed.


The visible effects above ground were remarkable—the leaves withered, fell off, and the stems turned brittle and brown. However, beneath the surface, the rhizome remained dormant, ready to sprout anew if disturbed or propagated. Jones soon realized that complete eradication was an unattainable goal. Some of his test plots now showcased mere remnants of lifeless knotweed canes, while alders and willows thrived alongside them. The once knotweed-infested lawn behind the house now flourished as a pristine expanse of grass. Yet, as I praised the transformation, Jones, ever vigilant, recounted an incident involving a woman who brought her dogs to the site, and they sniffed out the underground remnants—serving as a stark reminder that the knotweed was still there.


While there are more expensive options like encapsulation and excavation, the knotweed management industry in the UK generates over £165 million in revenue annually.


These approaches aim for complete eradication, regardless of the cost. On the other hand, some inventive methods have emerged, including a thermoelectric device resembling a cattle prod that promises to boil the rhizome, using diesel to douse gardens, or even employing goats to graze on the knotweed.


The Department for Environment, Food and Rural Affairs has conducted careful trials involving imported insects to curb the plant's growth, but experts like Jones remain skeptical of such solutions, questioning their effectiveness and practicality in the face of the widespread knotweed infestation in Britain. Jones firmly places his trust in glyphosate.


The groundbreaking discoveries made by Jones, Bowes, and their contemporaries have alleviated the concerns that plagued the early 2010s. Just last year, the Royal Institution of Chartered Surveyors (RICS) revised its guidance on knotweed, reducing the recommended radius of concern from seven meters to three meters—an indication of a more nuanced approach to management. While knotweed remains a formidable foe, we now possess better tools to keep it in check.


However, amidst the growing commercial industry with its valuations, protocols, damages, and bank scrutiny, the plant's true identity as a natural being often fades from view, overshadowed by its status as a pestilence. Jones, reflecting on his childhood in Cardiff, shared memories of encountering knotweed in a brownfield site near a rugby ground. He fondly recalled creating hideouts within the knotweed,


Marvelling at its rapid growth during the summer holidays. It was the only moment in our conversations when Jones displayed anything other than animosity towards the plant. When asked if he found knotweed, with its creamy-white flowers, beautiful in any way, Jones grimaced, unable to see its allure.

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