Elm Disease and its Distribution

Abstract

FOR the fifth year in succession the Forestry Commissioners have had a survey made on the status of the elm disease (Graphium ulmi). First observed on the Continent in 1919, and in England in 1927, the disease is now common throughout western and northern Europe, and more recently its occurrence has been noted on a few trees so far away as Ohio in the United States. In England between 1927 and 1931 it increased steadily both as regards the number of outbreaks and the damaging effect on the trees. The most notable feature in this year's survey is the reduced virulence of attack in nearly every area visited. It is quite impossible to say whether this diminution is merely a temporary check in the progress of the disease or the first sign of recovery. Elm bark beetles have long been suspected as being the principal means by which the disease is spread and this has now been proved to be the case. A great deal of work has been carried out in Holland on the relative resistance to attack of the various species of elms. So far only certain Asiatic species have proved immune and for the most part these are small trees unlikely to take the place of the English elm. All kinds of elms ordinarily planted in England appear to be susceptible; but, judging from the investigations conducted in Holland, there is some foundation for the hope that completely resistant forms of the common species may yet become available.