Surveys on Phytophthora disease of alder in UK
In 1993, a new lethal disease of common alder (Alnus glutinosa) was reported in Southern Britain, UK (see EPPO RS 95/010, 96/041). By early summer 1994, investigations showed that the diseased alders were quite widespread on the banks of streams and rivers, but also in places at some distance from waterways. The disease mainly occurs on A. glutinosa, but also on A. incana (grey alder) and A. cordata (Italian alder). It was established that the disease was caused by an usual form of Phytophthora cambivora, a well-known pathogen of broad-leaved trees such as Castanea, Fagus and Malus (but previously unknown on Alnus). Surveys were carried out in southern England and east Wales, on an area of 70 000 km2. Data was collected from 63 observation plots. In 1994, 3.9 % of trees showed crown symptoms and 1.2 % trees were dead (although not all were killed by the disease). The combined percentage of symptomatic and dead trees rose to 6 % in 1995 and to 7.9 % in 1996. It was also noted that a positive correlation existed between disease incidence and high levels of nitrate in waters. At present, it is still not clear whether this unusual form of P. cambivora is a new fungus introduced into Europe and spreading there, or if it is a native fungus whose damage is increased by environmental changes such as water pollution. As of June 1998, this Phytophthora disease has also been observed in Austria, Denmark, France, Germany, Netherlands (EPPO RS 98/023), Sweden, but with a variable severity. In addition to UK, tree mortality has only been reported from some places in Austria, France and Sweden.
Sources
Gibbs, J.N.; Lipscombe, M.A.; Peace, A.J. (1999) The impact of Phytophthora disease on riparian populations of common alder (Alnus glutinosa) in Southern Britain.
European Journal of Forestry, 29(1), 1-88.
Web site of the UK Forestry Commission
http://www.forestry.gov.uk/research/summary.html