FOREWORD 



One of the hazards of international trade is the possible move- 

 ment of dangerous insects and pathogens accompanying the exchange 

 of agricultural and forest products. To illustrate, of the major plant 

 pests and diseases that cause losses in excess of a billion dollars an- 

 nually and necessitate costly control programs in the United States, 

 over half were introduced from other continents. Included among 

 the major introduced diseases are three that have taken and continue 

 to take a tremendous toll from North American forests: chestnut 

 blight, white pine blister rust, and Dutch elm disease. All practical 

 precautions should be taken to prevent the introduction of additional 

 dangerous forest pathogens and every effort made to provide ad- 

 vance information on eradication or control procedures for those 

 that may be accidentally introduced. 



The accomplishment of these objectives is dependent on interna- 

 tional cooperation to recognize and characterize those forest tree 

 pathogens in each continent considered to be potentially dangerous 

 if introduced to other continents and to promote measures to restrict 

 their spread. To that end. the Forest Service of the United States 

 Department of Agriculture has participated in the work of the In- 

 ternational Union of Forestry Research Organizations, particularly 

 in the activities of the Working Group on International Cooperation 

 in Forest Disease Research. The report of this Working Group to 

 the 13th Congress of the parent organization in Vienna in 1961 is 

 a significant contribution to improved forest disease prevention and 

 control in all lands. The Forest Service, therefore, welcomes the op- 

 portunity to publish it for worldwide distribution and use. 



This publication is truly the result of cooperative effort. It as- 

 sembles under one cover the reports of 37 scientists from 14 countries 

 in Asia, Europe, and North America. It includes descriptions of 

 57 forest pathogens in the Northern Hemisphere considered to be 

 potentially most damaging to forest production in other continents, 

 with recommendations for special precautions to restrict their inter- 

 continental spread. These diseases occur on 87 genera of forest trees, 

 of which 50 genera are important in the United States. 



The text of the separate reports is with few exceptions as sub- 

 mitted by the various authors. No attempt has been made to adopt 

 a uniform system of nomenclature for pathogens and hosts. 



This publication is a Supplement to Section 24-11 of the Pro- 

 ceedings, 13th Congress, International Union of Forestry Research 

 Organizations, Vienna, 1961. 



V. L. Harper 



Deputy Chief. Forest Service 

 U.S. Department of Agriculture 

 (Vice President, IUFRO) 



m 



