LESSENING THE THREAT OF 



INTERNATIONALLY DANGEROUS TREE 



DISEASES 



A. J. KlKER 



Professor of Plant Pathology and Forestry. 

 University of Wisconsin, Madison, Wisconsin, U.S.A. 



The maintenance of sustained yields in high quality timber is 

 one of the prime aims of research in forestry. Among the enemies of 

 sustained yields are the following: fire, insects, animals, inroads of 

 "civilization,"' and diseases. In the disease category one finds not 

 only the pathogenic agents that destroy foliage and kill trees, but also 

 those that cause root, butt, and trunk rot. In the United States, the 

 total growth impact of forest diseases is estimated to be about 45 per- 

 cent of the losses caused by all destructive agents. 



In Xorth America the invasion of foreign forest tree diseases has 

 caused tremendous losses. Examples are chestnut blight, white pine 

 blister rust, and Dutch elm disease. The latter is insect borne. The 

 importance of injurious insects that might come from abroad also is 

 clearly recognized. However, the insects are outside the scope of the 

 present consideration. 



Epidemic diseases are much more serious for forest trees than for 

 comparable agricultural crops. If a field of wheat should be de- 

 stroyed, something else could be planted the next year. But, if the 

 trees are damaged, then 10, 25, or 50 years of the productivity of the 

 land may be reduced or lost. Furthermore, with some of the root 

 and butt rot organisms another danger appears. Such pathogens may 

 develop in an apparently innocuous way in the nurseries. Thus, dan- 

 gerous disease organisms may be distributed with the nursery stock 

 used for reforestation throughout the areas. 



A program has been initiated to investigate (1) what the chances 

 are that certain internationally dangerous diseases might be moved 

 from one country to another, (2) how this movement could be pre- 

 vented, or at least slowed down, (3) how quarantines could be made 

 more effective, (4) how eradication might be accomplished if a foreign 

 disease should appear, (5) how its damaging effects might be avoided 

 or reduced if it appeared and could not be eradicated, and (6) how 

 research might supply badly needed information about the host, the 

 pathogen, and disease development. To facilitate such a program, the 

 writer visited sixteen different countries to consult with leading for- 

 esters, quarantine officials, forest geneticists, and pathologists. His 

 trio was financed by the University of Wisconsin. 



Xumerous suggestions on what to do have come from many compe- 

 tent people. A summary appears below : 



Directory of Critical Tree Diseases. — In order to have available 

 information about the epidemic diseases and their importance in each 

 country, annotated lists of them have been, or are being, prepared in 



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