Phytophthora disease of alder (Alnus glutinosa) in France:: investigations between 1995 and 1999

A severe decline of alder associated with an undescribed Phytophthora species was identified for the first time in England in 1993. No generalized decline of alder was reported in France before 1990. The first diebacks and mortalities of common alder were observed at the beginning of the 1990s, but the so-called alder Phytophthora was not isolated in France until 1996. First, a synthesis about alder declines that were known in France before 1995 is presented. Then, a survey was established in north-eastern France; 108 sites were visited and the alder Phytophthora was isolated from 57 of them. All the main rivers were found to be affected and damage levels are significant along some of them. The frequency of the alder Phytophthora and other fungi isolated from declining alders is discussed. Finally, information on other alder declines in France is presented region by region, and a map summarizes the known distribution of the disease. The alder Phytophthora is quite common and widespread in France, with western and north-eastern France being especially affected; however, the number of diseased or dead trees varies greatly from one site to another. All records are from Alnus glutinosa; other Alnus species were seldom seen in the surveys.