Diseases and Pests of the Apple and Their Control 239 



(1) Insecticides for biting insects — arsenate of lead, 

 paris green, calcium arsenate and arsenite of zinc. 



(2) Insecticides for sucking insects — lime-sulfur, 

 nicotine solution, miscible oils, so-called dry-lime-sulfur 

 compounds. 



For biting insects. 



Arsenate of lead is the most widely used poison for chew- 

 ing and biting insects. It is particularly effective against 

 the codlin-moth. Both powdered and paste forms are in 

 common use, the powder having come into recent popular- 

 ity on account of convenience in handling. Of the two 

 kinds of lead arsenate, one is known as ortho, triplumbic 

 or neutral lead arsenate and the other as standard or 

 diplumbic lead arsenate. The diplumbic or acid lead is 

 now being employed almost to the exclusion of the ortho 

 or triplumbic form, although the latter is sometimes recom- 

 mended for more tender foliage or in regions where foliage 

 is likely to be burned by arsenicals. Best brands of paste 

 lead contain from 15 to 17 per cent of arsenic oxide, while 

 powdered forms usually contain approximately double that 

 amount, the 50 per cent water-content having been 

 removed. Two pounds paste or 1 pound arsenate of lead to 

 50 gallons of water are standard strengths. Before the 

 lead is added to the spray-tank, it should be made into a 

 thin paste by the addition of water or preferably reduced 

 to a solution in 3 or 4 gallons of water. Particular atten- 

 tion should be given to mixing the powdered forms so that 

 the suspension will be complete. Strengths of less than 2 

 pounds of paste lead arsenate to 50 gallons of water have 

 not as a rule given satisfaction. ' At present a number of 

 experiments are being conducted in the Northwest in 



