UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 866 
SL&*&Jl> 
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. 
1 
2 
6 
22 
Page 
Results of investigation— Continued. 
Apples 29 
Cranberries 37 
Suggestions for the preparation of Pickering 
spray on a commercial scale 42 
Summary '. 44 
Bibliography 46 
INTRODUCTION. 
When, in 1916, the price of copper sulphate (bluestone 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 
i 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 Farms, N. J., and 
J. E. Sullivan, Superintendent of Aroostook Farm, Maine. 
180971°— 20— Bull. 866 1 
