CONTROL 211 



are likely to die during the absence of the particular plant 

 on which they are accustomed to feed. 



In considering the best treatment for plant diseases, 

 a question may arise as to whether the trouble is really of 

 bacterial origin. Often this is difficult to determine with- 

 out the aid of a good microscope. This difficulty, how- 

 ever, is of little practical importance to farmers. It is 

 desirable to use knife and fire to destroy the diseased 



PEACH ROT. 

 Each eruption is made up mostly of thousands of germs, called spores. 



parts of plants affected seriously by any sort of blight, 

 soft rot, or gall growths ; and when a field crop has been 

 diseased, it is wise not to sow it again in the same field for 

 three or four years. The Bordeaux Mixture which will 

 be described in 158 is supposed only to protect healthy 

 plants, not to cure diseased parts. 



In fighting plant diseases we should remember that we 

 ought to strive for prevention rather than cure. The 

 reason we destroy plants or parts of plants with conta- 

 gious diseases is in line with our practice of quarantining 

 people afflicted with scarlet fever, and with the practice 



