SELECTING AND PREPARING MATERIALS 273 



upon the host. The time of application of control measures 

 is influenced by this fact. 



Some fruit diseases, as fire blight of apples, pears, and 

 quinces, are caused by bacteria rather than fungi. Since they 

 are already established on the host before their presence is de- 

 tected, and since any materials that would control them would 

 also injure the host plant, they must be fought by methods 

 other than spraying. 



Various physiological diseases as bitter pit, drought spot, 

 and cork are apparently associated with poor moisture con- 

 ditions, and injury from these troubles is reduced when mois- 

 ture conditions of the soil are improved. 



(c) Consult Experiment Stations and Other Sources for 

 Complete Information. The experimental stations and colleges 

 of agriculture are public agencies, established in the various 

 states. They are prepared to furnish the latest and most de- 

 pendable information available with regard to the insects and 

 diseases that trouble the grower. The grower should establish 

 and maintain contact with these institutions as a safeguard 

 and insurance. 



The commercial grower cannot afford to turn a business 

 enterprise into an experimental project. He may, however, 

 cooperate with public agencies in conducting field laboratories, 

 tests, and demonstrations that have for their object the ac- 

 quirement or dissemination of greater knowledge, which in 

 turn will bring a larger return to the grower. 



2. Selecting and Preparing Materials for Control. Ma- 

 terials suitable for controlling certain insects may be ineffective 

 against others, and may be useless for the control of diseases. 

 Some materials possess valuable properties for both insect and 

 disease control. Some are effective, but cost so much that the 

 grower cannot afford to use them; others are effective and 

 acceptable as to cost but cause injury to the plant or fruit 

 under certain conditions. New materials are continually 

 being put forward, and the grower must decide whether or 

 not he will discard the old and adopt the new. 



