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BIOLOGICAL METHODS FOR THE CONTROL OF 
PLANT DISEASES AND NEMATODES 
George C, Papavizas, 
Crops Research Division, Agricultural Research Service, 
U.S. Department of Agriculture, Beltsville, Md. 
Economically profitable methods of at least 
partial control by use of chemicals and resist- 
ant varieties have been developed for a great 
many plant diseases and parasitic nematodes. 
Despite this fact, crop disease losses in the 
United States average about $4 billion per year, 
or nearly one-tenth of the potential annual 
production (41), Several crop diseases of aerial 
plant parts and a large number of soilborne 
82 
diseases and nematodes have byno means been 
brought under significant control. Many of the 
uncontrolled pathogens have such a wide range 
of host plants that no feasible crop rotations 
can be devised; or they are so unspecific and 
omnivorous in their nutritional requirements 
that finding resistant varieties appears to be 
a remote and time-consuming possibility. A 
few diseases of aboveground plant parts and 

