APPLE POWDERY MILDEW AND ITS CONTROL. 17 



frequently results from the use of acid arsenate of lead applied after 

 the early foliage has developed. 



SPRAYING FOR APPLE SCAB. 



Considering the climatic conditions of the Pajaro Valley, one 

 might expect apple scab to become a serious disease of the fruit, and 

 for that reason its relative absence is the more striking. Occasionally 

 scab does considerable damage in scattered orchards, but in those in 

 which the writers have carried on investigations in its control it has 

 never been sufficiently abundant to make the experiments satisfactory. 

 It is therefore not of sufficient importance in this district to require 

 regular attention in spraying. Apple scab, in the degree in which it 

 is present, is the only fungous disease of the fruit occurring in the 

 Pajaro Valley. 



GENERAL FORMULA FOR THE SPRAY MIXTURE. 



Stock iron-sulphid mixture 1 20 gallons. 



Arsenicals and nicotine solution to be added as required. 



Water, to make 200 gallons. 



When arsenicals and a nicotine solution are to be used in conjunc- 

 tion with the iron-sulphid mixture, the combined spray may be 

 prepared by first running about 150 or 160 gallons of water into the 

 spray tank. The agitator is then started and the 20 gallons of stock 

 iron-sulphid mixture is poured in, after which the nicotine solution 

 and the arsenicals may be added in the usual way. Sufficient water 

 should then be added to make 200 gallons. 



This same strength of iron-sulphid mixture, namely, 20 gallons in 

 200 gallons of spray, is to be used in all of the mildew applications. 

 It will be seen that the 20 gallons of stock mixture used in each 

 200 gallons of spray contains the product from 4 pounds of iron 

 sulphate. If commercial iron-sulphid preparations or other com- 

 mercial products containing sulphur in very finely divided form are 

 employed, they should be used in such quantities as to give the same 

 sulphur content as the above amount of iron-sulphid mixture, or, 

 better, the optimum dosage for mildew control should first be deter- 

 mined by experiments, since the fineness of the product will influence 

 its effectiveness and therefore the amount to be used. 



SPRAYING SCHEDULE. 



The following spraying schedule for the control of apple powdery 

 mildew has been worked out for the Pajaro Valley in particular, but 



1 See page 15,' " Preparation of the iron-sulphid mixture.'' 



