Japanese knotweed (Fallopia Japonica) belongs to the problematic non-native plants (neophytes). The plant originates from the far east and has spread rapidly through Central Europe, the British Isles as well as the United States, causing major damage to dams, walls and streets due to its powerful growth. Furthermore it destroys native plants and endangers biodiversity.
In the West of the German federal state Baden-Württemberg, public offices have been dealing with this issue for more than thirty years. In the Ortenau region, dams have been damaged since Japanese knotweeds destroyed sod causing high water to penetrate into building structures, resulting in fatal problems with their stability.
The regional board of Freiburg reports on studies to control Japanese knotweed with hot steam.
Conventional mechanical methods such as mowing and mulching are not able to diminish the population, they only hinder spread. At present the only remedy available are broad band herbicides such as Round-Up, which are not completely safe. Hence they cannot be used in close proximity to water due to their water damaging effects. Furthermore, they have to be applied over several years in order to significantly decrease the population.
For these reasons, the regional board of Freiburg decided to study the effect of hot steam on larger contaminated areas. In September 2009 about 500 square meters of afflicted soil was excavated down to 30 cm depth to fully remove the soil layers mainly infested by the plant rootstock. The contaminated excavation was steamed in a specially prepared trailer. The steamed ground was put back and the area re-natured.
The lowland adjacent to the river is paved with stones and was specially treated. Since excavation of infested soil was impossible due to the pavement, areas were gradually covered with special steaming hoods and treated. Since then the steamed areas are supervised by staff of the regional board (Mr. Keller, Mr. Martin) and by staff of MSD GmbH (Moeschle-Seifert-Daempftechnik), which has supported the study with technical equipment and expertise.
In a second step, sprouting plant parts in deeper not treated soil layers will be partially steamed with steaming lances reaching up to 1 m into the soil.
Prior to the study MSD GMBH and the association for sewage treatment Offenburg (Mr. Mohn) has already made an initial study in the beginning of 2009. Due to the highly positive results yielded in this first trial, in which no shoots occurred more than half a year after steaming, positive results are expected for the next study as well.
For more information on Japanese knotweed, please check on Wikipedia Wikipedia.