UNITED STATES DEPARTMENT OF AGRICULTURE 
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WASHINGTON, D. C. PROFESSIONAL PAPER April 5, 1923 
THE INFLUENCE OF COPPER SPRAYS ON. THE 
an oy COMPOSITION OF IRISH POTATO 
ERS. 
By F. ©. Coox, Physiological Chemist, Insecticide and Fungicide Laboratory, 
Miscellaneous Division, Bureau of Chemistry. 
CONTENTS. 
Page. Page. 
Purpose of investigation__________ 1 | Results of experimental work—Con. 
Results of previous investigations: Influence of strength and num- 
weieldoor potatoes. =. 2 aos ee 2 ber of applications of copper 
Composition of potatoes ______ 3 sprays on composition of 
Pl antse ce SeCNeT Al 2 4 tubers #2. 2 eee eee 17 
Experimental procedure___________ 7 | Influence of environment on com- 
Results of experimental work : MOSsition Of. tupeESs | — eee 18 
Changes in composition of tubers Copper content of vines, stems,. 
Gunns! -STOw theese SE es bs tl roots, and tubers of sprayed 
Effect of copper sprays on yield and unsprayed plants ______ 19 
and composition of tubers___ 10 |" General ‘discussion == aaa 21 
Proportion of tubers to vines Summ anya 5 te ee ee 23 
DLS. GUDeCISS sos eke ee Gel iteracure’ Cited. = oe a eee 24 
PURPOSE OF INVESTIGATION. 
For years Bordeaux sprays have been applied to the potato plant 
to control fungous diseases, particularly in the northern parts of the 
country where the late blight (Phytophthora infestans) frequently 
causes serious losses. In those parts of the Central and Southern 
States where potatoes are grown the only spray ordinarily applied 
igs an arsenical to control the Colorado potato beetle. Arsenicals are 
‘usually added to the Bordeaux sprays. The formule of Bordeaux 
sprays may vary in different localities. A 5-5-50 spray is one in 
which 5 pounds of copper sulphate and 5 pounds of lime are used 
and the spray is made to 50 gallons with water. 
The fact that potato plants treated with Bordeaux spray give 
larger yields of tubers than those which do not receive such applica- 
tions‘ has been established by a series of experiments extending over 
many years at the Vermont, Maine, and New York agricultural ex- 
periment stations. The influence of the copper sprays on the com- 
position of the tubers, however, has received no detailed study in this 
country. In view of the importance of the potato crop it is surpris- 
ing that practically no detailed analyses of potato tubers grown in 
the United States are available. 
meager pa se oy 
