THE DUTCH ELM DISEASE 

 A NEW THREAT TO THE ELMS 



By Malcolm A. McKenzie, Assistant Research Professor of Botany and 

 William B. Becker, Research Assistant in Entomology 1 



Since 1930, when the Dutch elm disease was first discovered in the United 

 States, all persons interested in our principal shade tree have become increas- 

 ingly alarmed as the number of elms known to be affected with this disease has 

 steadily mounted. From 1930 to 1932 the known cases of the disease in 

 America were limited to less than a dozen trees in Ohio. During the last three 

 years, however, nearly 22,000 cases of the Dutch elm disease have been found 

 in New Jersey, New York, Connecticut, Indiana and Maryland. Up to this 

 time (May 1937) the disease has not been found in Massachusetts. 



This publication aims to present to the people of Massachusetts the essential 

 facts concerning the dread Dutch elm disease and to urge every one in the State 

 to cooperate in the effort to protect and preserve our elms. 



THE DISEASE 

 Distribution 



As the name implies, the Dutch elm disease was first observed in the Nether- 

 lands; and, since the discovery by the Dutch in 1919, thousands of elms in 

 European countries have been killed by the disease. Reports from Europe 

 indicate that the disease exists throughout the extensive range of climatic and 

 soil conditions included in the following countries: Netherlands, France, 

 Italy, Austria, Belgium, Switzerland, Germany, Poland, Czechoslovakia, 

 Balkan States, and Great Britain. The disease is widely distributed in England 

 but has not as yet been found in Scotland. 



In the United States, the most serious infestation of the disease at present 

 is found on the eastern seaboard in New Jersey, New York, and Connecticut. 



In both Europe and North America, the only continents where the disease 

 has been observed, elms and trees of the closely related genus Zelkova are 

 apparently the only hosts upon which the disease occurs in nature. A few 

 species of elms are reported to be resistant to the disease, but none is known 

 to be immune and the American elm (Ulmus americana L.) is very sus- 

 ceptible. 



Investigation into the source of the disease in America led to the discovery, 

 a few weeks after the finding of the disease in New Jersey, that burl-elm logs 

 from Europe which were intercepted at the ports of New York, Baltimore, 

 Norfolk, and New Orleans were carriers of the causal fungus. European elm 

 bark beetles from which the fungus was isolated were also found to be present 

 in the logs. It appears probable that at least fifty-eight shipments of elm logs 

 which in some cases are now known to have been diseased and beetle-infested 



'The writers are indebted to Profs. A. Vincent Osmun and Arthur I. Bourne, respectively in 

 charge of botanical and entomological investigations, for valuable assistance, suggestions and 

 criticisms during the preparation of the manuscript of this bulletin. Acknowledgment is also made 

 to Miss Gladys I. Miner, Herbarium Curator, for the preparation of the photographic negative 

 used in the lower half of the frontispiece; and to the Division of Forest Pathology, United States 

 Department of Agriculture, and the New York State College of Agriculture, Cornell University, 

 for the use of photographs wherever credited to these sources. 



