Heating soil successful in combating Japanese knotweed

Published on
February 18, 2020

Japanese knotweed (Fallopia japonica) is an invasive exotic plant, whose strong roots and stems cause significant damage. Hitherto, there were no effective control measures available. Recent research by Wageningen University & Research (WUR) shows that an innovative heating technique kills 99 per cent of this parasitic plant in sandy soils.

The Japanese knotweed, which originates in Asia, was brought to the Netherlands as a garden plant. The plant is found in a large variety of locations in the Netherlands: In urban areas, along railway tracks, in derelict areas, along roadsides, riverbanks, on the edge of forests, along creeks and dykes. Its presence causes a decline in indigenous flora and damages buildings, roads and pipes. This leads to increased expenditure for repairs and maintenance.

Treating the soil

Treating just the part of the plant that is above ground, is no solution because the stems below ground remain intact and continue to sprout. Commissioned by Van Gelder Aannemingsmaatschappij and Van den Herik Zuigtechniek, WUR, Probos and Tree-O-Logics studied whether heating the soil with the help of a mobile apparatus could cleanse the soil to a degree sufficient to eradicate any living remains of the plant.

Heating the soil to reduce the number of Japanese Knotweeds
Heating the soil to reduce the number of Japanese Knotweeds

To this end, soil was gathered in six different locations where the Japanese knotweed occurs. The collected soil was strained and subsequently treated using the prototype of the mobile heating apparatus. The soil was then studied for seven weeks to determine if any regrowth occurred.

Heating appears effective

Heating the soil after straining significantly reduced the number of root stem fragments and living shoots. The number of vital fragments was reduced by 99%, in comparison to soil that was only strained. Whether this result can be achieved in real-life situations depends largely on the thoroughness with which the ground is excavated. Furthermore, it is essential that an aftercare plan is developed for instances where a single root fragment survives the treatment.