COPPER SPRAYS ON IRISH POTATO TUBERS. iy 
The results reported in this paper appear to establish the fact that 
copper sprays not only increase the yield of potatoes in various sec- 
tions of the country, but favorably influence their composition.? 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 appears to 
exert a stimulating action on the potato plant. 
Bordeaux and 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 wide y 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 44-50 Bordeaux spray 
was applied eight times, compared with results where the same spray 
* Attention is called to the experiments of Gray and Ryan, 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. 
