What You Need To Know About Knotweed

History Of Knotweed

Carl Peter Thunberg, a Swedish naturalist, first discovered Japanese Knotweed in the late 1700s. It was discovered again between 1823 and 1829, by Philipp Franz Balthasar von Siebold, a naturalist and Bavarian doctor who worked for the Dutch army. von Siebold set up a nursery in Leiden in Holland, where he distributed this plant throughout Europe in 1848. Due to the benefits of its immense success after receiving the Gold Medal award at Utrecht from the Society of Agriculture and Horticulture in 1847, he started aggressively marketing the plant. Using the plant’s ability to create dense screens and its robust growth habit as two of the main selling points, Knotweed was marketed as a type of ornamental fodder plant and its abilities to act as a stabiliser in sand dunes. Sales became widespread.

When Did Knotweed Reach The UK?

In the year 1850, the Leiden Nursery sent an “unsolicited parcel” to the Royal Botanical Gardens at Kew. This parcel also included Japanese Knotweed. In the year 1854, a specimen of Knotweed was sent to the Royal Botanic Gardens in Edinburgh. A nursey based in Kingston was one of the earliest nurseries to start selling Knotweed in Britain in the same year. From here it was distributed and sold by many amateur enthusiasts and commercial nurseries. By 1886, the plant became naturalised in the UK.

The Dangers Of Knotweed Was First Identified In The Late 19th Century

As the Nineteenth Century came to an end and the start of the Twentieth, the hazards of this plant started to become apparent. A report of flora present in Alexandra Park in Oldham, which was published in 1887, mentioned how Knotweed continued to appear “unexpectedly in just about every portion of the cultivated ground”. Gertrude Jekyll, who was once an enthusiast when it came to Dwarf Japanese Knotweed (Fallopia japonica var. compact), stated that Knotweed should be carefully planted and here once-beloved Dwarf Knotweed should be reduced (in 1899). In the year 1905, the Royal Horticultural Society cautioned its readers in their Journal of the Royal Horticultural Society to rather not plant Japanese knotweed, unless the plant was “most carefully kept in check”.

By this stage, it was already too far gone to reverse the adverse impact of this plant, and the status of knotweed continues to increase and it is invasive. Despite the many warnings, the British government only produced legislation in 1981 to specifically control its spread and sale.

Knotweed The “Menace” Outside Its Natural Environment

Knotweed only turned into a global menace when it left its “natural” environment in Asia. When growing in its natural and native habitat the plant is kept under control by several natural means. In Japan, there are at least 6 fungus species and 30 insect species that feed on these plants. Outside this natural environment, these species don’t exist, and without these natural predators, the Knotweed continues to thrive.

Trials To Control The Growth Of Knotweed

In the UK, trials have been actively conducted to allow for the release of the common natural predators of Knotweed from Japan into Britain without causing knock-on effects on other species. If you are looking for a Knotweed Specialists then see here.

Aphalara itadori, a type of psyllid was released into a controlled area to manage Knotweed naturally. However, scientists are still saying more time will be needed to decide whether this project was successful, even though the bugs were released five years ago.

Once released, it will take many years to have real effects (usually between 5 to 10 years). These agents will only control the plant rather than eradicate it. At the same time, these bugs will feed only on Japanese Knotweed and not on any related or hybrid species.

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