This chapter is concerned with the way in which studies on particular sites have informed our understanding of pathogen dissemination and disease development. It supplements the more detailed observations on the relationship between the pathogen and the host described by Londsdale (Chapter 7). The chapter is divided into two sections. The first deals with the disease as it occurs in relation to trees in riparian habitats - where trees grow on the banks of rivers and other bodies of water. A link between the disease and watercourses was suspected as soon as the preliminary UK surveys in September 1993 showed that trees in a broadly similar state of disease could be found along lengthy tracts of affected streams (Gibbs, 1995). During the last few years, studies have been initiated on many riparian sites and this work is reported here. Datasets for disease development in three countries are summarised. The second section discusses the occurrence of the disease in non-riparian sites. That the disease could occur in non-riparian sites was also recognised back in 1993, when the pathogen was isolated from symptomatic trees in a young woodland plantation in east Wales, UK (Gibbs, 1995). Studies on this site quickly lead on to an investigation of planting stock as a source of infection and this work, now extended to a number of European countries, is described here. In addition, data from studies of disease in other non-riparian sites such as orchard shelterbelts are presented.
