EN
Common alder (Alnus glutinosa) and grey alder (Alnus incana) are distributed along streams, rivers and increasingly planted in programmes of riverbank restoration. Since over a dozen years dying of alder trees has been observed in Europe. Phytophthora spp. are the major pathogens of this plant. In 2004 Brasier at al. described new species, especially aggressive to alder as P. alni which is an interspecific hybrid between P. cambivora and P. fragariae. A new Phytophthora disease of alder is widely distributed in Europe. The paper summarizes information on the morphological characteristics, isolation procedure, modes of spreading and possibility of disease limitation.