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Japanese knotweed biological control

Knotweed, known as itadori in Japan, possesses a captivating allure with its poetic nickname "tiger cane." This name draws inspiration from its tall canes resembling the stripes of a tiger's back. However, despite its native ecosystem constraints, knotweed prevails, engaging in fierce competition with silvergrass and bamboo for essential resources. The plant faces a minuscule insect that feeds exclusively on its sap, gradually weakening and killing it. Nevertheless, itadori thrives, seizing neglected land as its own.

Koichi Watanabe, an Osaka photographer, recalls encountering a mysterious plant during his childhood walks along a riverbank. This plant, sprouting after the removal of a dense black locust forest, surprised him with its asparagus-like buds and heart-shaped leaves. Unfamiliar with it, he later discovered that it was the ubiquitous itadori, flourishing abundantly.

Over the past 20 years, Watanabe embarked on a global journey to capture the essence of knotweed through his photographs. His project, aptly named "Moving Plants," explores the concept of plants traversing the world by intertwining with human lives, challenging the perception of plants as stationary beings. In his mesmerizing images, knotweed groves take center stage, showcased in expansive horizontal panoramas that allow glimpses of human existence within the frame. While the Japanese, like most locals, show indifference towards itadori, considering it of minimal ornamental value, Watanabe encountered unexpected uses derived from the resilient plant, such as itadori leaf tea, jam, and pickles found in some supermarkets.

While Japanese authorities label knotweed as a pest, necessitating its routine clearance from riverbanks and farms, the general public's stance is less extreme. Watanabe expressed his shock upon hearing the words "eradicate" or "kill" in relation to knotweed during his time in England.

The tolerant attitude towards knotweed in Japan can be attributed, in part, to its confinement within its natural habitat, rarely encroaching upon Japanese gardens.

Daisuke Kurose, a plant pathologist who extensively mapped knotweed across southern and northern Japan, attests to its absence on private properties, even in rural areas, leading to less concern among the populace. Kurose shares an interesting anecdote from his university lectures, where students often mistakenly assume itadori to be a bird due to the similarity between "dori" and the Japanese word for bird. While Kurose acknowledges the hardships knotweed has caused, he also feels empathy for the British people who struggle to eradicate this strong and resilient plant.

Watanabe's exploration of knotweed extends beyond Japan, taking him to the UK, Poland, the Netherlands, and both coasts of the US. However, he has yet to visit France and Sweden, where knotweed proliferates extensively.

Knotweed, known as "parkslide" in Sweden has managed to spread as far north as 65 degrees latitude, and the upcoming milder winters are expected to facilitate its further expansion. Jonathan Lindgren, an executive at Villaägarna, a Swedish homeowners' association, recounts frantic conversations with municipalities grappling with knotweed infestations. Lindgren mentions unsuccessful attempts, such as using pigs to consume knotweed, and expresses exasperation at the growing problem that seems to be a losing battle.

Some enthusiasts ascribe spiritual properties to knotweed due to the presence of resveratrol, a compound also found in wine. Lindgren highlights the existence of YouTube videos and blogs that even recommend intentionally growing knotweed or using it to make pies.

Chris van Dijk, a Dutch knotweed researcher, regularly encounters knotweed emerging from the crevices of Amsterdam's canals, with its rhizomes causing significant damage that could lead to collapsing walls. In Rotterdam's harbor, dense knotweed colonies necessitated the removal of 120,000 cubic meters of contaminated soil. Watanabe's photos capture striking scenes of knotweed invading wheat fields, choking irrigation canals, and engulfing the base of a house in upstate New York. These images give the impression of a colossal digestive process frozen in time, where only the upper floor of the house remains visible, but even it will eventually succumb to the knotweed's devouring embrace if left unattended.

Throughout his visits to these sites, Watanabe feels an eerie sensation as if he has entered a future world devoid of human presence. He envisions a landscape where vegetation regenerates year after year in the absence of human structures. In this transformed environment, hybridized itadori would reign supreme. However, Watanabe does not perceive these scenes as snapshots of a vegetal apocalypse.

Instead, he silently connects with his subject, marveling at the graceful dance of knotweed's leaves in the breeze. Gradually, he develops sympathy for knotweed, lamenting the way people often speak of it as if it were a virus or a pest. He emphasizes that humans are responsible for introducing knotweed across the globe and subsequently losing their minds over its presence. In Watanabe's eyes, itadori is not guilty; it is merely living.


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