SCALE INSECTS. 23 



and quality of soap used has much to do with results at- 

 tained. Whale-oil soap is far superior to any other kind. 

 In this soap, however, there are different qualities. The 

 soap, to be most suitable, must not at the given amount 

 used become a glutinous, stringy mass upon cooling. 

 Common soap and many of the fish-oil soaps will do this 

 It is not very difficult to secure the death of 75 to 90 

 per cent, of the scale. It is the remaining 10 to 25 per 

 cent., which if allowed to survive will soon replace the 

 fallen, that demands strong solutions and thorough appli- 

 cation. 



Effects of Wash. — Upon Scale. The young scale lar- 

 vae during growth are killed almost immediately, death to 

 mature scale results slowly, due to time required for i^ene- 

 tration of insecticide and the action of weather upon scales 

 loosened by the wash. Two months are sometimes required 

 ±o determine fully the exact results obtained. 



Upon Tree. — The fall application increases vigor and 

 growth of tree. The following year a heavier, brighter 

 foliage appears, but the bloom and fruitage are noticeably 

 less. In spring, at blooming time, no perceptible effects 

 could be noticed from the wash. 



Gas Treatment. Where large orchards must be treated 

 or a number of orchards are quite generally infested, the 

 work had better, as in California, be given by contract to 

 parties owning complete apparatus and being familiar with 

 best methods of application. This plan is highly advisa- 

 ble, since the d*eadly effects of the gas make its use by in- 

 experienced persons extremely dangerous. In short, the 

 treatment is as follows : The tree is covered by a tent 

 made of blue or brown drilling, or eight-ounce duck painted 

 or oiled to make air-tight. The gas generated beneath this 

 tent is made from one ounce fused cyanide of potassium 

 (58 per cent, pure), one ounce of sulphuric acid, and three 

 fluid ounces of water to every 150 cubic feet of space to be 

 fumigated. This treatment is rarely used against the San 

 Jos6 scale except in case of nursery stock, where cyanide of 

 potassium of much greater strength (98 per cent.) is used. 

 On dormant nursery stock, the space of 150 feet may be re- 



