18 Diseases of Economic Plants ,| 



of that crop. Rotation breaks the continuity and hinders i 



the multipHcation of the parasite. 



13. Avoidance of practices that aid in dissemination of 

 the parasite. — Examples: bean pod-spot, tomato leaf-spot. 

 In certain instances the spore of the causal fungus is trans- 

 ferred from plant to plant most freely when the host is wet. 

 To avoid picking or cultivating under such conditions is to 

 lessen the spread of infection. Similarly in the greenhouse, < 



surface watering may spread the spores. By sub-irrigation 

 this may he avoided. 



The importance of sanitary methods cannot be over- 

 emphasized and stress on such methods rather than on the 

 employment of specific treatment against disease is a growing 

 tendency. Many crops from their very nature are but j 



slightly amenable to direct treatment; others will not need ] 



it if they are given surroundings that are, in general, sanitary. | 



Increased attention should, therefore, be given to soil condi- ] 



tion both chemical and physical, to the fitness of the crop to 

 the particular soil and climate, to water relations, to crop 

 rotation, to closeness of planting, ventilation, to proper seed 

 selection, and modes of propagation. 



