Coliar rot of beech in NW-Germany is mainly caused by Phytophthora cambivora. Rarely also P. citricola and P. pseudosyringae were found in the rhizosphere of diseased trees. On certain sites the disease has completely destroyed mature beech stands in a slow decline like process extending over many years. If such sites are replanted with young beeches, these may be infected and killed by P. cambivora within a shorter time. Preliminary observations indicate that young beeches originating from natural regeneration may be probably less infected than planted ones. Such damage is mainly found on soils with high Calcium saturation (Ca/CECeff/tot. > 50 %), rarely at medium Ca/CEceff/tot. of 20-30 %, and rarely or not at all at low Ca-saturation (Ca/CECeff/tot. < 13 %). It is concluded that Ca-saturation may be the major site factor controlling the occurrence and severity of the disease. Elevated clay content of the soil may also enhance disease development, however less so than elevated Ca-saturation. On sandy soils with low clay content the disease enhancing effect of clay many be replaced by high precipitations, provided that the soil has a sufficiently high Calcium saturation. In mixed plantations on sites favouring the occurrence of Phytophthora spp. beech (Fagus sylvatica) was by far the most susceptibel, followed by maple (Acer pseudoplatanus) and still less infected cherry (Prunus avilum), while all other species, including ash (Fraxinus excelsior), hornbeam (Carpinus betulus), elm (Ulmus glabra) and lime (Tilia cordata) exhibited complete field resistance. In oak (Quercus robur) field resistance is probably restricted to young stands, while old stands on limy sites suffer decline due to fiber root rot caused by Phytophthora species. These field observation were largely confirmed by inoculation experiments, except for oak, which got infected after experimental inoculation, while it showed no visible damage in forest plantations. For silvicultural prevention on risky sites it is recommended to replace beech by some of the less susceptible broad leaf species, which are well adapted to these sites.
