﻿COPPER SPRAYS ON IRTSH POTATO TUBERS. 23 



The results reported in this paper appear to establish the fact that 

 copper sprays not only increase the yield of potatoes in various 

 tions of the country, but favorably influence their composition. 2 Bor- 

 deaux sprays, Pickering sprays, and barium-water sprays seemed to 

 give the increased yield and increased solids of the tubers which 

 apparently depend on the presence of copper in the spray. In addi- 

 tion to plant-disease control and insect control, the copper appeals to 

 exert a stimulating action on the potato plant. 



Bordeaux an(i other sprays containing copper are usually applied 

 to the potato to control the late blight. In some States such a spray 

 is applied as a repellent to the flea beetle and the potato leafhopper, 

 thereby reducing the injury to the foliage from these two insect pests 

 and at the same time lessening tip burn and hopperburn. The im- 

 portance of the effect of copper sprays on the yield of potatoes, in 

 addition to their control of diseases and insects, has not been gener- 

 ally recognized or at least emphasized. Nor has the fact that tubers 

 from copper-sprayed plants may be stored more satisfactorily — that 

 is, with less loss from rot — than tubers from noncopper-sprayed plants 

 been widely advertised. When, in addition, an increased yield of 

 potatoes and a higher proportion of solids in them follow the appli- 

 cation of copper sprays, important additional reasons for their more 

 general use become evident. 



SUMMARY. 



Tubers from copper-sprayed potato plants at the time they were 

 large enough for analysis (about one inch in diameter) were usually 

 higher in solids, starch, and nitrogen than the tubers from un- 

 sprayed vines. The starch content increased approximately 50 per 

 cent as the tubers matured, while the dextrose disappeared and the 

 sucrose was materially reduced. The early varieties of potatoes 

 showed a decrease in their sugar content to accompany an increased 

 starch content in the copper-sprayed tubers during the early stages 

 of development. The proportion of insoluble ash decreased during 

 the growth of the tubers, although the total ash content remained 

 constant. The total nitrogen increased. The figures for soluble, 

 coagulable, and particularly the monoamino and amid nitrogen 

 increased as the tubers matured. 



The proportion of tubers to green vines appeared to be higher for 

 the copper-sprayed than for the unsprayed plants. 



Average data for seven States obtained in 1919 showed the food 

 value of an acre of copper-sprayed potatoes to be 839 pounds more 

 than that for an acre of noncopper-sprayed potatoes. Two factors, 

 increased yield (48 bushels an acre) and an increase of solids (5.6 

 per cent), are involved. 



Some results obtained at Arlington Experimental Farm, Va., 'com- 

 paring a 10-10-50 Bordeaux and a 5-5-50 Bordeaux, suggest that 

 the former spray has no advantage over the latter and may possibly 

 furnish too much copper for the maximum stimulating or protective 

 effects. Results from New Jersey, where a 1-1 50 Bordeaux spray 

 was applied eight times, compared with results where the same spray 



2 Attention is called to the experiments of Gray and Rvan, Monthly Bull. Dept. Agr. 

 State of California, Chemical Number, vol. 10, no. 1, pp. 11-33, 1921. They showed that 

 the acidity of oranges was reduced by the arsenical spray. 



