PREVENTION AND CONTROL 273 



the application of the preceding rules of this chapter 

 might give much better results. 



However, in many cases we must spray for the 

 reduction and destruction of certain classes of disease 

 organisms. Spraying should be done at the proper 

 time and in the proper manner, and not only for the 

 purpose of curing the diseased plants, but for the 

 protection of the healthy ones ; in fact, the protection of 

 the healthy plants is usually of much greater importance 

 than the curing of diseased plants. 



When the organism of disease is confined to the 

 surface or very near the surface of the plant, it may be 

 possible to effect a cure by the use of the spray, but 

 when the organism penetrates the tissues of the plant 

 it is beyond the reach of the spray so far as curing .that 

 individual plant is concerned. However, the spray will 

 kill the spores which may be formed on that plant, and 

 thus in a measure prevent the spread to neighbouring 

 plants and other parts of the same plant. The spray 

 on healthy plants will also prevent the germination of 

 the spores which may have been carried from diseased 

 plants. Spraying is of no value whatever in the treat- 

 ment of diseases due to bacteria. 



The use of a fungicidal spray may also be detri- 

 mental if applied at such times as to interfere with the 

 fungi which are destructive to injurious insects. Fungi- 

 cides and spraying apparatus and their uses will be 

 considered in the next chapter. 



Quarantine. Diseases are frequently introduced from 

 one country to another on plants and seeds, and even 

 upon commercial products. Some of the most de- 

 structive diseases have been carried in this manner. 

 Plants or seeds should never be transplanted from one 

 country to another without being subjected to rigid 

 inspection and quarantine. In fact, it is sometimes 

 advisable to institute inspection and quarantine between 

 districts of the same country. To this end, such laws, 

 should be enacted as will be protective but not burden- 

 some to the population. 



T 



