Insect and Disease Control 239 



to kill the insects beneath their protective scale covering 

 will seriously injure the f()liaf]:e. 



Spraying may be done in the fall, or during mild periods 

 in the winter when it is practicable to work in the orchard, 

 or in the spring before the buds have swelled very much. 

 Badly infested trees are sometimes sprayed twice, in the 

 fall and again later. Such trees may well be headed back 

 considerably to increase the thoroughness of the spraying, 

 since it is practically impossible to cover the small limbs 

 completely with the spray mixture. 



Fumigating nursery stock. 



As previously stated, one of the most common and far- 

 reaching means by which the San Jose scale has been dis- 

 seminated has been through the distribution of infested 

 nursery stock. To overcome this menace to the fruit in- 

 dustry, a method of treating nursery trees with hydrocyanic 

 acid gas before they were shipped from the nursery was 

 worked out early in the history of this insect in the East. 

 This treatment is required by law in some states. 



The requisites for efficient fumigation of nursery stock 

 are : (1) a gas-tight box or building (depending on the 

 amount of stock to be treated) in which the trees are placed ; 



(2) a supply of potassium cyanide, 98 to 99 per cent pure ; 



(3) commercial sulfuric acid testing about 66° Baume, 

 that is, a grade approximately 93 per cent pure ; (4) water. 



Many nurserymen have constructed houses especially 

 designed for this purpose into which a wagon loaded vMi 

 nursery stock can be run and treated without unloading. 



Trees that are to be treated should be in a dormant con- 

 dition and should not be wet, that is, no free moisture should 

 be on the surface. 



