UNITED STATES DEPARTMENT OF AGRICULTURE 





Contribution from the Bureau of Chemistry 

 CARL L. ALSBERG, Chief 



Washington, D. C. 



August 24, 1920 



PICKERING SPRAYS. 



By F. C. Cook, 1 Physiological Chemist, 

 Insecticide and Fungicide Laboratory. 



CONTENTS. 



Introduction. 



Results of previous investigations. 

 Purpose of present investigation. . 



Preparation of sprays used 



Results of investigation : 



Potatoes 



Grapes 



Page. I Page 



1 ; Results of investigation— Continued. 



2 Apples 29 



6 Cranberries 37 



7 Suggestions for the preparation of Pickering 



spray on a commercial scale 42 



8.1 Summary 44 



22 i Bibliography 46 



INTRODUCTION. 



When, in 1916, the price of copper sulphate (bhiestone or blue 

 vitriol) rose to 25 and 30 cents a pound in certain parts of the country, 

 the United States Department of Agriculture began to receive many 

 inquiries as to the possibility of controlling certain fungous diseases 

 of fruits and vegetables, either by using sprays other than those 

 containing copper or by reducing the amount of copper sulphate 

 used per given amount of spray. Past work having failed to show 

 any fungicides which could replace the copper sprays for certain 

 important plant diseases and the search for a new spray appearing 

 rather unpromising, it seemed advisable to seek a copper spray 

 which was more effective per unit of copper than the standard 

 Bordeaux mixture and at the same time not so caustic as to injure 

 vegetation. Accordingly, the Bureau of Chemistry, in cooperation 

 with the Bureau of Plant Industry and the Maine Agricultural Ex- 

 periment Station, undertook an investigation to determine the com- 

 parative efficacy of the so-called Pickering sprays, which had been 



1 The author wishes to express his appreciation of .the cooperation he received from J. K. Haywood,. 

 Bureau of Chemistry; from W. B. Clark, H. A. Edson, L. H. Evans, W. A. Orton, J. W. Roberts, E. S. 

 Schultz, C. L. Shear, M. B. Waite, E. Wallace, and R. B. Wilcox, of the Bureau of Plant "Industry; 

 from Donald Folson, W. A. Morse, G. B. Ramsey, and C. D.Woods, of the Maine Agricultural Experi- 

 ment Station; and from Franklin Chambers, Superintendent of Whitesbog, Hanover JF arms, -N. J., and 

 J. E. Sullivan, Superintendent of Aroostook Farm, Maine. 



180971°— 20— Bull. 866 1 



