10 BULLETIN 712, U. S. DEPAETMEXT OF AGRICULTURE. 



.resulted in injury. In some cases intense burning sunlight has not 

 occurred until fully two weeks after the spraying was completed, 

 but still severe burning of the fruit resulted. 



The adoption of adequate spraying methods is largely dependent 

 on the safety with which they may be used. The data secured 

 on injury in connection with the use of various sprays during the 

 course of the experiments reported below will therefore be of value 

 in pointing out the weather conditions under which burning occurs, 

 the type of injury resulting, and the time at which the sprays may be 

 safely applied. These data are presented in connection with the ex- 

 periments herein reported. 



ORCHARD SPRAYING EXPERIMENTS. 1 



The orchards used were adjacent to each other and for the 

 purposes of this work can be considered as one. The trees use'd 

 were a solid block of the Pryor Red and Jonathan varieties, the 

 experimental plats each consisting of adjacent rows of seven trees 

 each, while the Black Ben Davis plats comprising a like number of 

 trees were located in double rows extending across the orchard. The 

 trees were 14 years old at the beginning of the experiments in 1915. 



The Pryor Red trees have a very open habit of growth, and al- 

 though they had been cut back severely to bring them into more 

 workable shape they still had a spread of about 30 feet and were 

 about 30 feet high. When in full foliage they required about 25 

 gallons of spray material per tree. The Black Ben Davis trees 

 were not spread out as much, but were more compact and dense. 

 They required about 20 gallons of spray material each. The 

 Jonathan trees were smaller than those of the Black Ben Davis and 

 more open, requiring about 10 to 15 gallons of spray material per 

 tree. All had been infected with mildew for several years, the dis- 

 ease being especially severe in 1914, when the crop of the Pryor Red 

 trees was reduced to an average of 2 bushels each, although the trees 

 were otherwise capable of producing at least 30 bushels. The Black 

 Ben Davis and Jonathan trees had produced a somewhat heavier 

 crop than those of the Pryor Red, but in every case the foliage and 

 twig growth had been seriously infected and many terminal branches 

 had been killed. 



The experiments were undertaken to determine — 



(1) The most effective fungicides for use against apple powdery mildew. 



(2) The most desirable dates for spraying. 



(3) The possible toxic effects of the various spray materials tested. 



A high-power spraying outfit of 200-gallons capacity was em- 

 ployed, a pressure of 200 to 250 pounds was maintained, and eddy- 



1 These experiments were carried out at Wenatehee, Wash., in the orchards of the 

 V. & W. Land & Improvement Co. and of Mr. A. P. Kornbau, to whom acknowledgment is 

 due for many courtesies extended during the course of the investigations and for active 

 cooperation at all times. 



