﻿COPPER SPRAYS ON IRISH POTATO TUBERS. 7 



Dudley and Wilson (13) report that the potato leafhopper is one 

 of the most important enemies of the potato in the United States. 

 Bordeaux repels the leafhopper and therefore effectively controls 

 the potato leafhopper and hopperburn. According to Fenton and 

 Hartzell (18) , the leafhopper can be effectively controlled and hop- 

 perburn can be prevented by covering the potato plants with Bor- 

 deaux spray. This spray keeps the adult insects from laying their 

 eggs on the plants and kills many of the young insects. 



EXPERIMENTAL PROCEDURE. 



Three kinds of sprays containing copper were used in the experi- 

 mental work reported here: (a) Ordinary Bordeaux spray, pre- 

 pared by mixing milk of lime and copper sulphate solutions; (b) 

 Pickering spray, prepared by mixing a saturated solution of lime- 

 water with a dilute solution of copper sulphate; and (c) a barium- 

 water spray, prepared by mixing barium hydroxid with a dilute cop- 

 per sulphate solution. These sprays are discussed fully in United 

 States Department of Agriculture Bulletin 866. 



The yield data were obtained from the two middle rows of a 4-row 

 plot. Care was taken to select for these experiments plants which 

 were as free as possible from late blight, mosaic, leaf roll, etc. The 

 tubers from six plants receiving the same treatments were placed in 

 a sack and immediately taken to the laboratory for analysis. For 

 each analysis six medium-sized tubers were selected from the sam- 

 ple and the analyses were made the day on which the tubers were 

 dug. All of the samples were run through a Herles press which gives 

 a very finely divided product. All determinations were made in 

 duplicate, the average figures being recorded in the tables. With 

 the exception of the 1921 data, which include detailed analyses, only 

 solids, starch, and total nitrogen determinations are reported. 



Solids, ash, insoluble ash, sugars, total nitrogen, and phosphorus 

 were estimated by the methods of the Association of Official Agri- 

 cultural Chemists (3). Starch was determined by the Herles method 

 (23) which depends upon the conversion of the insoluble starch to 

 a soluble starch by means of hydrochloric acid and a reading of the 

 percentage of soluble starch in the polariscope. Copper (9) was 

 estimated on 10 grams of the dried sample by the colorimetric pro- 

 cedure, using potassium ferrocyanid. Soluble nitrogen, soluble phos- 

 phorus, ammonia nitrogen, coagulable nitrogen, and nitrogen as 

 monoamino and amid nitrogen were estimated on water extracts 

 of the finely-divided samples of tubers as previously outlined by the 

 writer (10) . The pH data were obtained on the water extracts of 

 the tubers, using the colorimetric procedure of Clark and Lubs (7). 



RESULTS OF EXPERIMENTAL WORK. 

 CHANGES IN COMPOSITION OF TUBERS DURING GROWTH. 



During the season of 1921 tubers from four varieties of potatoes 

 grown at Presque Isle, Me., were analyzed. Some of the plants 

 had been sprayed with copper sprays, while others had not. The 

 tubers were analyzed at various periods during their growth in order 

 to determine when the influence of the copper sprays was exerted, 

 and also to show the changes that take place in the composition of 

 American-grown tubers during their development. These data are 

 given in Table 1. 



