ARSENICAL RESIDUES AFTER SPRAYING. 



W. C. O'Kane, C. H. Hadley, Jr., and W. A. Osgood. 



(A list of references will be found at the end of this bulletin. 

 The numbers in parentheses in the text refer to these cita- 

 tions.) 



INTRODUCTION. 



The experiments described in this bulletin have been in progress 

 during the last five years, beginning with the year 1912. They 

 were undertaken with the intention of discovering the possi- 

 bility of danger resulting from residues of arsenate of lead remain- 

 ing on fruit or foliage after spraying with that material. 



The immediate circumstance leading to the investigation was 

 the invasion of the browntail moth in New Hampshire apple 

 orchards. Altho many orchard owners adopted the practice of 

 cutting off the winter nests of this pest, the fact remained that 

 this treatment, while effective in avoiding injury the next spring, 

 resulted in more or less unfavorable trimming of the trees. It 

 was found that a poison spray applied to the foliage about the 

 first week in August killed the young caterpillars when they 

 first hatched from the egg and before they had opportunity to 

 make up the winter nest. This spraying in August was, there- 

 fore, recommended. 



Immediately, the question arose as to the possible danger that 

 might result to persons eating fruit from trees sprayed at this 

 time in the growing season, especially in the case of eaily fruit, 

 which would be nearly or quite ripe at the time such spray was 

 applied. Along with this arose the question of possible poisoning 

 of live stock allowed to graze beneath trees so sprayed, or fed on 

 hay cut from beneath such trees. 



The investigation at first contemplated only experimental 

 spraying, and analyses of the residues on fruit from such trees. 

 At the close of the season it appeared wise to expand the in- 

 quiries, in order properly to interpret the results of the analyses. 

 Sufficiently detailed or accurate data as to the poisonous piop- 

 erties of arsenate of lead did not appear to be in existence. 



The study was, therefore, widened to include experiments 



