Japanese Knotweed (Reynoutria japonica) is a species of herbaceous perennial plant in the Polygonaceae family, native to eastern Asia. It has been 𝐢𝐦𝐩𝐨𝐫𝐭𝐞́𝐞 𝐞𝐧 𝐄𝐮𝐫𝐨𝐩𝐞 𝐚𝐮 𝐗𝐈𝐗𝐞 𝐬𝐢𝐞̀𝐜𝐥𝐞 𝐝'𝐀𝐬𝐢𝐞 used as an ornamental plant. Indeed, its bamboo-like stem and bright green, heart-shaped leaves were a big hit in gardens. Since then, humans have encouraged its spontaneous spread through certain activities, such as backfilling building sites. Particularly dynamic, it thrives along the banks of rivers and lakes, especially in brightly lit areas. The 𝐞𝐧𝐯𝐢𝐫𝐨𝐧𝐧𝐞𝐦𝐞𝐧𝐭𝐬 𝐚𝐫𝐭𝐢𝐟𝐢𝐜𝐢𝐚𝐥𝐢𝐬𝐞́𝐬 (rockfill, road embankments, railway embankments, etc.) are favourable to its development.) are favourable to its development, which can be observed in both lowland and mountain regions. However, despite all its advantages, it does have one drawback: it is a 𝐩𝐥𝐚𝐧𝐭𝐞 𝐧𝐨𝐧-𝐢𝐧𝐝𝐢𝐠𝐞̀𝐧𝐞 𝐭𝐫𝐞̀𝐬 𝐞𝐧𝐯𝐚𝐡𝐢𝐬𝐬𝐚𝐧𝐭𝐞.
In Switzerland, it is blacklisted as an invasive plant with a degree of 𝟏𝟎 𝐬𝐮𝐫 𝟏𝟎 𝐝'𝐮𝐫𝐠𝐞𝐧𝐜𝐞 𝐝𝐞 𝐥𝐮𝐭𝐭𝐞 because it represents a real 𝐝𝐚𝐧𝐠𝐞𝐫 𝐩𝐨𝐮𝐫 𝐥𝐚 𝐛𝐢𝐨𝐝𝐢𝐯𝐞𝐫𝐬𝐢𝐭𝐞́ 𝐥𝐨𝐜𝐚𝐥𝐞 : its vegetative reproduction and the fact that it suffers virtually no parasitic attack encourage its growth, which can reach 𝐣𝐮𝐬𝐪𝐮'𝐚̀ 𝟖 𝐜𝐞𝐧𝐭𝐢𝐦𝐞̀𝐭𝐫𝐞𝐬 𝐩𝐚𝐫 𝐣𝐨𝐮𝐫! Thus, by forming very dense bushes, capturing all the surrounding light, it 𝐞𝐦𝐩𝐞̂𝐜𝐡𝐞 𝐥𝐞 𝐝𝐞́𝐯𝐞𝐥𝐨𝐩𝐩𝐞𝐦𝐞𝐧𝐭 𝐝𝐞𝐬 𝐚𝐮𝐭𝐫𝐞𝐬 𝐞𝐬𝐩𝐞̀𝐜𝐞𝐬 plants found around. What's more, it emits toxic substances through its roots that restrict the growth of native plants. The Association pour la Sauvegarde du Léman began the fight against this scourge in spring 2013, initially on the shores of Geneva, as part of 𝐬𝐨𝐧 𝐚𝐜𝐭𝐢𝐨𝐧 "𝐇𝐚𝐥𝐭𝐞 𝐚𝐮𝐱 𝐑𝐞𝐧𝐨𝐮𝐞́𝐞𝐬". Thanks to the regular help of volunteers who intervene between April and October, a 𝐫𝐞́𝐠𝐫𝐞𝐬𝐬𝐢𝐨𝐧 𝐝𝐞𝐬 𝐟𝐨𝐲𝐞𝐫𝐬 has been noted after 6 years of control. As of 2017, the action has been extended to the other cantons bordering Lake Geneva to provide sustainable assistance to Lake Geneva municipalities faced with knotweed colonisation. The ASL organises and coordinates uprooting operations to maximise their impact and contain the growth of knotweed, or even eradicate certain areas. The method used is not only proven effective, but also preserves native vegetation. In 2019, "Halte aux renouée" again extended to new foci in the cantons of Geneva and Vaud, but also in Valais and Haute-Savoie. 𝐀𝐢𝐧𝐬𝐢 𝐥'𝐚𝐧 𝐝𝐞𝐫𝐧𝐢𝐞𝐫, 𝟏𝟐,𝟒 𝐭𝐨𝐧𝐧𝐞𝐬 𝐝𝐞 𝐫𝐞𝐧𝐨𝐮𝐞́𝐞𝐬 𝐨𝐧𝐭 𝐞́𝐭𝐞́ 𝐚𝐫𝐫𝐚𝐜𝐡𝐞́𝐞𝐬 by the ASL and 132 outbreaks were treated.
More information on the ASL website page dedicated to the action Stop Knotweed
