238 The Commercial Apple Industry 



time it has not been altogether sucecssful in controlling 

 bad scab infection, excessive codlin-moth, or apple-blotch, 

 the three most serious apple diseases and pests. It seems 

 possible that dusting may prove better adapted to regions 

 where the codlin-moth is not particularly serious or scab 

 infection critical. For hilly orchards or orchards where 

 water supply is remote, or where liquid spraying is exceed- 

 ingly difficult, the use of dusting may be recommended as 

 a substitute. 



The power duster is usually operated by a two- or 

 three-horse-power gasoline engine. The dust mixture is 

 fed into a rapidly revolving fan by means of a hopper and 

 a strong current of air forces the dust out through a dis- 

 charge pipe. A single operator directs the cloud of dust 

 by shifting the discharge pipe. 



INSECTICIDES 



In studying insect control, the first consideration should 

 be given to the methods by which insects secure their food. 

 Generally speaking, there are two classes of insects: (1) 

 biting and chewing insects such as codlin-moth and tent- 

 caterpillar; (2) sucking insects such as aphids and scale. 

 When insects feed on such exposed parts as the buds or 

 leaves, arsenicals or other stomach poisons are necessary. 

 In the case of chewing insects which feed beneath the 

 bark, such as borers, other control methods must be em- 

 ployed. Sucking insects are best checked by the use of 

 contact sprays such as lime-sulfur, nicotine, and kerosene 

 emulsion. 



Following is a general classification of common insect- 

 icides : 



