Efficacité des méthodes de lutte contre le développement de cinq espèces de plantes invasives amphibies : Crassula helmsii, Hydrocotyle ranunculoides, Ludwigia grandiflora, Ludwigia peploides et Myriophyllum aquaticum (synthèse bibliographique)

Effectiveness of techniques used to control the development of five invasive amphibious plant species: Crassula helmsii, Hydrocotyle ranunculoides, Ludwigia grandiflora, Ludwigia peploides and Myriophyllum aquaticum. A review. Among rapidly spreading invasive species in Europe, amphibious plants are particularly problematic. These plants are capable of developing a photosynthetic activity both below and above the water surface, and they typically form dense floating populations. Controlling amphibious plants, whether for the purposes of total eradication or for the regulation of their spread, represents an important challenge for managers. A literature review of existing control methods for Crassula helmsii, Hydrocotyle ranunculoides, Ludwigia grandiflora, Ludwigia peploides and Myriophyllum aquaticu was carried out, taking into account efficiency and costs. Of the 87 studies analyzed, a great variation was evident in the research efforts undertaken (number and spatial scale of studies) between species and between control methods. However, overall, the different control methods described showed a similar level of efficiency between species. Reports of total eradication of amphibious plants were rare. Such cases resulted from the application of mechanical or chemical methods, most often coupled with complementary methods such as manual finishing. The use of chemical control methods (less laborious and costly than others) was found to be frequently documented in the literature. However, except in the case of some active substances, such chemical methods were found to provide low control efficiency. Similarly, to date, biological control has not been found to provide convincing results. In addition, it should be noted that several biological control agents are considered as invasive species in Europe. On the other hand, although little related research has been carried out, methods such as manual or mechanical removal with manual finishing have often been found to result in satisfactory control levels. Aware of the difficulty of controlling amphibious plants, as well as the potential collateral damage caused by control methods to aquatic ecosystems, we argue that consensus still needs to be found between scientists, decision-makers and managers before decisions at regional or national scale can be made.