The palm trees of the south of France will have to cohabit with the red palm weevil. Or disappear. In a report published Wednesday, the national Agency of environmental safety and health (Anses) considers that it is too late now to hope to eliminate this dreadful parasite that has been raging for ten years in the seven departments of the mediterranean coast and Corsica.
Reported for the first time in October 2006 in the town of Sanary (Var), the red weevil ( Rhynchophorus ferrugineus ), native of the island of Borneo, but probably introduced into France through shipments of palm trees imported from Egypt, has spread like wildfire. Its larva causes damage by feeding inside the trunk of the tree (or stipe) until death. “To this day, some municipalities have already lost between one-half and two-thirds of their palms,” says Roland Pélissier, general secretary of the regional Federation of fight and defence against harmful organisms (Fredon) of Provence-Alpes-Côte d’azur.
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the larva of The red palm weevil feeds on the interior of the stipe, the “trunk” of the palm trees. Guillaume SUEUR /guillaume06560 – stock.adobe.com
“in the Face of this scourge, we must not give up, but fight with realistic and achievable goals,” explains the Figaro , Philippe Reignault, one of the members of the group of experts which carried out this evaluation report at the request of the ministry of Agriculture.
Two control strategies are considered. The first is to “stabilize, if possible, the population of red palm weevil and to limit its area of geographic expansion,” according to the Anses, pointing out that the “cost will be high”. The other solution, less ambitious, it would merely limit the protection of certain palm trees, especially for their heritage significance” and to “propose to plant species replacement for areas not protected”. Like all types of palm trees are more or less attacked by the weevil, this would be the equivalent of planting other species of nature and appearance are quite different.
The second option is highly criticized. “It is illusory to pretend to protect such a palm tree rather than another, believes Roland Pélissier. If all trees of a given sector are not treated, the weevil will constantly reappear”. And cite the example of the Cavem, the agglomeration community of Fréjus-Saint-Raphaël, which has managed to substantially reduce the level of infestation of the 3000 palm trees identified on its territory in the middle of a chemical treatment systematic.
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In this respect, Anses has conducted the evaluation of the six combinations of chemical methods (benzoate émamectine injected into the sitpe) and biological: the application of a fungus ( Beauvaria bassinia ) or a nematode worm that attacks the weevil and its larvae and, finally, mass trapping using sex pheromones. Result: “when the criterion “cost” has been put forward strategies involving the injection of benzoate of émamectine combined or not in the mass trapping emerged as the most satisfactory” according to the report. On the other hand, “when the criterion “safety for the environment” has been overweight, it is the combination of two biological control products associated with the mass trapping which is one of the leading.”
“Failure of the State”
Elsewhere on the Riviera, where palm trees are rare, but where the weevil is still apparent (Morbihan in 2013, Normandy in 2017), the goal of eradication remains achievable according to the Anses, which cites the successful example of the Canary Islands. The report speaks of “exceptional result”, “result of a very quick reaction”, “centralized”, and with “average heavy”: insecticides, pheromone traps, embargo. But what is possible in an island setting is not necessarily in the mainland area. The case of Israel, also well documented in the report, shows how this country has managed to save, in a first time, orchards of date palms, by using a control mass, before being invaded a few years later. Meanwhile, the weevil was re-emerged in private sites and the affected municipalities had in general not taken on the responsibility of treating.
“The situation is similar for us. While the red palm weevil is classified on the list of harmful organisms since 2010, number of communes, starting with the Nice, have not complied with the order to fight the mandatory,” says Hervé Piétra, president of the association Save our palms pointing to a “failure of the State who has not been able to enforce the rules.”