Diseases of the Douglas Fir in Britain

Abstract

AS is often the case with exotics, there have been distinguish this attack one or two scares on the subject of diseases in connexion with the Douglas fir plantations in Britain. A fungus A fungus attack reported in a young plantation, when investigated, proved to be caused by an undescribed species of Phomopsis (P. Pseudotsugce Wilson). Then a species of Chermes (Chermes Cooleyi) appeared in several parts of the country. A recent leaflet (No. 18) issued by the Forestry Commission, deals with a disease new to Britain, the Douglas fir leaf-cast disease (Rhabdocline Pseudotsugce 8yd). The disease is common on the Douglas in the United States, but until within the last few years it had not apparently been noticed on the east of the Atlantic. It has been found on the blue form of the Douglas fir (Pseudotsuga glauca) and on the interior dry belt or Fraser River form (P. Douglasii var. cassia). Recently it has been also observed on the green Douglas (P. Douglasii). This fungus occurs on all forms of the Douglas in the United States, and occasionally becomes epidemic for a season or so. It usually only infests young trees, but attacks larger trees growing on poor quality soils.