PROBLEMS IN PREVENTING PLANT-DISEASE EPIDEMICS 77 



demies often sweep across several countries and therefore require interna- 

 tional cooperation in studying and controlling them. International coopera- 

 tion is not only desirable but essential in controlling many epidemic diseases. 

 What are the prospects for more complete and economical control of epi- 

 demic diseases? Obviously, the ideal way of controlling all diseases would be 

 by means of resistant varieties, but this has not always been feasible in the 

 past. Progress would be much more rapid in many cases if islands could be 

 made available where a world collection of presumably resistant varieties 

 could be tested against a world collection of races of their principal patho- 

 gens, without danger of contaminating agricultural areas. The alternative is 

 to make tests in many places of the world in the hope of providing an ade- 

 quate sample of existing pathogens. Much more needs to be learned about 

 the nature and variability of resistance and about the possibility of inducing 

 it by nutritional or other procedures. Much more needs to be learned about 

 the genetics, the physiology, and the ecology of pathogens ; much more needs 

 to be learned about the physiology of parasitism and about mutual relations 

 between pathogens and other microorganisms, especially to find out whether 

 antibiotic organisms can be used to help man in his fight against plant 

 diseases. 



What are the possibilities of revolutionizing chemical control? Most chemi- 

 cals now used are essentially protective rather than therapeutic in their action, 

 and most of them must be applied to growing plants frequently and in rela- 

 tively large quantities. Many epidemic diseases that attack aboveground 

 parts of plants could be prevented by chemical dusts or sprays if the plants 

 were grown in small gardens instead of extensive fields. Even the cereal rusts 

 can be controlled in this way. But what would be the expense of dusting 50 

 million acres of wheat in the United States, with 2.5 million culms on each 

 acre, with sulfur or other dusts several times each season? Disease control 

 could be revolutionized if chemicals could be applied once a season in homeo- 

 pathic doses. Chemicals are urgently needed that can be applied in small 

 quantities and that have permanent and systemic effects, a sort of chemical 

 immunization. 



Epidemic diseases of plants are tremendously important, and it is there- 

 fore tremendously important to understand and control them. To attain deeper 

 and broader understanding and to devise more efficient and economical con- 

 trol measures will require the services of highly competent research scientists, 

 very skilled technologists, and far more adequate facilities. Scientific compe- 

 tence and physical facilities must be commensurate with the complexity and 

 magnitude of the problems. The improvement and protection of plants is 

 basically of paramount importance to peoples everywhere. And the services 

 of all branches of botanical science, pure and applied, are needed to preserve 

 past gains and to assure future progress. 



