Apple Spraying Experiments in 1916 and 1917. 109 



io in 1917 were the same as those used on plots 6, 5, 4, 1, 3, 9 

 and 8 respectively in 191 6. 



Two new features were included in the 191 7 experiments 

 in order to obtain farther light on the question of the fungicidal 

 action of arsenate of lead in controlling apple scab. Plot 8 was 

 sprayed with standard dilution lime-sulphur alone with no ar- 

 senical added, in order to secure a check on this point from 

 another angle. On plots 1 and 7 a different form of arsenate of 

 lead was used than that previously employed. 



The writer's first observations indicating the possible value 

 of arsenate of lead in controlling apple scab were made quite 

 unexpectedly in 1912 in connection with this series of experi- 

 ments. For the most part it has been the custom to utilize for 

 experimental work the same supply as that bought for general 

 use as an insecticide on the farm orchards. In the earlier work 

 no attention was paid to the character of the material used, 

 whether it was acid, neutral, or basic, or a mixture of two or 

 more of these different forms. Samples were saved from the 

 lots used in 1915 and 1916 and analyses of these samples by the 

 Chemical Department of this Station showed that each, although 

 purchased from different manufacturers, was practically of the 

 same composition as a pure acid, or lead hydrogen arsenate. 

 No accurate data is obtainable as to the composition of the ma- 

 terials used in former years. However, a study of the reports 

 of analyses of the same brands as were used in these years, 

 based upon samples taken by the inspection service from goods 

 on sale in the State, shows that in all probability these results 

 showing a fungicidal action on apple scab have been obtained! 

 throughout the series of experiments with an acid arsenate of 

 lead, previous to 191 7. 



"Taken as a whole, the literature indicates that there are 

 at least two common lead arsenates, lead hydrogen arsenate 

 and lead orthoarsenate ; that these two compounds are the main 

 components present in ordinary commercial lead arsenate "* 



The authors of the publication just quoted made a very 

 thorough chemical study of the subject of the arsenates of lead 

 used in spraying. Among other things, they attempted to pre- 



*Robinson, R. H. and Tartar, H. V. The Arsenates of Lead. Bui. 

 Ore. Agl. Exp. Sta. 128, p. 6, 1915. 



