88 



by packing the trees in a air-tight room and subjecting 

 them to the fumes of hydrocyanic acid for thirty-five 

 minutes. The gas is generated by treating chemically 

 pure potassium cyanide with the best grade of commer- 

 cial sulphuric acid at the rate of 1^ oz. of cyanide, If 

 oz. of acid and 5 oz. of water to every 150 feet of cubic 

 space in the room. 



Preliminary Treatment. 



Unfortunately there seems to be no satisfactory sum- 

 mer treatment for the San Jose scale, and winter appli- 

 cations must be chiefly depended upon for the control of 

 this pest. However, it is not infrequent that summer 

 spraying can be done to advantage. This insect mult- 

 plies at a rapidly increasing ratio during the breeding 

 season until checked by cold weather about the middle 

 of November or later. In this climate, therefore, the 

 period of greatest reproduction among the scale insects, 

 and consequently of greatest damage to the infested 

 trees, is from about the middle of September to the mid- 

 dle of November. Trees that are only slightly infested 

 in July may become encrusted with scales by November. 

 Frequently this rapid fall multiplication of the scale, 

 if left unchecked, results in the death of a great many 

 trees before a winter wash can be applied. 



The value of late summer or fall spraying in checking 

 the progress of the scale has been determined not only 

 by our experiments, but also by practical work in large 

 orchards. A 10 per cent, strength (or even 15 per cent, 

 when carefully used) of kerosene or crude oil applied 

 in mechanical mixture with water, or in soap emulsion, 

 does not materially damage peach trees in foliage and 

 does destroy large numbers of scale insects, especially 

 the recently issued young and a considerable per cent, of 

 the breeding females. During the breeding season the 

 progress of the scale should be watched, and if it threat- 

 ens to kill or impair the infested trees before winter 

 sets in, two or three applications of oil should be made. 

 These may be made at intervals of two or three weeks, 

 as occasion seems to demand, but even two applications 

 on successive days or with one day intervening, are con- 

 siderably more effective than a single one. The trunks 

 and larger limbs should be thoroughly sprayed, but 



