Ausmaß und Verbreitung der Phytophthora-Erkrankung der Erlen in Bayern, Ausbreitungswege und mögliche Gegenmaßnahmen

2003

S. 246-251

23 Lit. Ang.

Unselbständiges Werk

200099700

A detailed survey of Phytophthora root and collar rot of common (Alnus glutinosa) and grey alder (A. incana) along rivers and streams in Bavaria was performed by the Bavarian State Forestry and the river authorities in autumn 2001. The results show that the disease is present in riparian stands growing along more than 50 % of the river systems. Along some rivers the disease incidence exceeds 50 %. In 58 out of 60 rivers and streams which were investigated in detail the source of inoculum could be traced back to infested alder plantations established within the last 15 years on the river banks or on forest sites that are draining into the rivers via ditches. Once introduced into a river system, the 'alder phytophthora' spreads downstream infecting the collar or bare roots of riparian alders via lenticells and adventitious roots. A disease survey was also performed by the Bavarian State Forestry in 3247 forest stands of alder. The disease was present in 1041 stands (32.1 %) covering 1655 ha (45.2 %). Random controls indicate a high number of unknown cases. The "alder phytophthora" was recovered from 160 out of 179 diseased alder stands tested. 842 of the 1041 diseased stands were younger than 20 years. 395 of these young stands (46 %) were growing on non-flooded sites, among them 356 were planted (92 %) indicating disease transimission via infected nursery stock. Baiting tests from nursery grown alder plants supported this hypothesis. The "alder phytophthora" was present in rootstocks of alders from three out of four nurseries which regularly bought in alder plants from big nurseries for resale, but not in rootstocks from four nurseries that grow hteir own alder plants from seeds. In addition, the infected nurseries used water irrigation from infested water courses irrigation. As a consequence, a code of good practice for the production of alders was negotiated between the Bavarian State Ministry for Agriculture and Forestry and most of the Bavarian nursery owners. First results from coppice trials with diseased alder stands growing under flooded and non-flooded conditions indicate that coppicing may not be a reasonable measure for the sanitation of infested alder plantations. As a consequence, a series of permanent plots are currently being established in diseased alder plantations with variable disease incidences and different site conditions in order to get informations on disease development, necessary for decisions on silvicultural management. Furthermore, a program was started for screening for resistent alders in the field.