Japanese Knotweed
organic treatment
18.06.25
Success of bespoke
organic compost in treatment of Japanese Knotweed
JAPANESE Knotweed (Reynoutia Japonica) is a herbaceous
perennial native to East Asia. Commonly found on
volcanic slopes, its extensive root system allows it to
quickly reemerge following eruptions, producing large
amounts of nitrogen-rich leaves and carbon-heavy stems.
As these decompose, they contribute to new soil
formation. Knotweed can grow in a variety of soil types,
habitats, and ph conditions but tends to favour
disturbed, low diversity, bacterially dominated soils
with little organic matter and high light exposure.
In Ireland, knotweed is considered an invasive alien
species (IAS) and each year it costs the Irish State and
private individuals significant sums to treat and
mitigate its impact. It is frequently treated with
glyphosates (e.g. Roundup) to control spread.
Glyphosates are non-selective and if incorrectly managed
can impact adjacent plants and the biosphere more
generally.
In 2021, Donegal County Council teamed up with Inishowen
Rivers Trust and KPM Soils to pilot a small scale
experimental treatment of knotweed utilising a bespoke
organic compost.
In 2022 with the support of the Office of Public Works
and LAWPRO, the pilot was expanded. With the new
partners onboard, a successful application titled KNOT
(knotweed novel organic treatment) was made to the
highly competitive Public Services Innovation Fund (PSIF).
The KNOT project included six sites total, five in
Inishowen and one in Letterkenny Town Park. With Dr
Trish Murphy PhD in the Inishowen Rivers Trust looking
after project management and reporting, the scientific
and operational lead on the ground for the project was
KPM Soils, led by Kevin Moore and Dr Claire Moore PhD. |
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Pictured at one of the KNOT
pilot sites are (L to R), Gareth McKane, OPW; Shane
McMonagle, DCC; Claire and Kevin Moore, KPM Soils and
Jimmy McVeigh, LAWPRO. |
The treatment method
utilises KPM Soils expertise on soil regeneration to
establish soil conditions which are less favourable to
IAS such as knotweeds and more conducive to native
species. Specifically, KNOT aimed to assess the impact
of increasing fungal communities in the soil, enhancing
organic matter, and providing shade through dense tree
planting. Increasing the fungal component of the soil
promotes higher ecological succession, creating
conditions that may inhibit knotweed growth.
Treatment and monitoring continued on the pilot sites
through 2023 and 2024 with promising results achieved on
most of the sites. There have also been challenges,
particularly regarding hedge cutting activities.
Unfortunately, though the pursuit is usually
well-meaning, it has unwittingly impacted the cover
planting which was placed as part of the treatment
process and increased the ongoing risk of knotweed
spread.
However, challenges aside, the treatment has shown great
potential, and it is hoped to continue the pilot into
2025. Donegal County Council is also exploring the
possibility of implementing the treatment method at
other strategic sites impact by knotweed within the
county. |
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