INSECTS AND DISEASES 45 



organism are usually unknown; the form in which 

 the insect does its damage and the manner of its 

 attack are likewise unfamiliar. The result is that 

 much of the spraying done in the past, and even at 

 the present, is mere guesswork. Insecticides and 

 fungicides of various kinds are applied when it hap- 

 pens to be inconvenient to do other work and in 

 many cases the wrong organism is blamed for the 

 damage being done. Under these conditions treatment 

 is unsatisfactory, and the grower becomes dis- 

 couraged in every effort to fight the common pests. 

 With so much available information as to the kinds 

 of materials to use and their exact methods of ap- 

 plication some brief discussion of the more funda- 

 mental things usually neglected will be more to 

 the point. 



The importance of the subject, however, seems 

 to justify some further discussion of the insect and 

 disease problem from the larger standpoint. There 

 can be no question but what insects and diseases are 

 much more common at the present time than they 

 were formerly. Many of my older readers will 

 remember when there were no potato bugs or potato 

 blight ; no San Jose scale, codling moth, or many of 

 the numerous insects and disease now so frequent 

 and so destructive in the orchards and gardens of 

 the country. The question naturally arises as to 

 why these later days are so filled with these pests. 

 In the first place, by cultivation man forced many 

 insects to change their habits. Formerly they fed 

 upon plants of no particular commercial importance 

 to man. They were held in check by the natural 

 enemies of the forest and field, and development 

 was, therefore, retarded, and their damage was 

 comparatively insignificant, or at least unnoticed 



