20 BULLETIN 866, U. S. DEPARTMENT OF AGRICULTURE. 



Lot /.—The copper of the Pickering sprays adhered to the leaves 

 in proportionally greater amounts than that of the Bordeaux spray. 

 Per unit of copper sulphate in the spray more copper was deposited 

 on the leaves sprayed with the three Pickering sprays which contained 

 the highest percentages of copper sulphate than on those sprayed 

 with Bordeaux, but less on the leaves treated with the other Pick- 

 ering sprays. The results for copper on the leaves sprayed with 

 barium water were low. Of the leaves treated with the 3-3-50 and 

 3-1^—50 sprays those receiving the 3-1^-50 spray showed the largest 

 deposits. 



Lot 2. — As a rule, more copper adhered to the leaves sprayed with 

 Bordeaux than to those to which any of the other sprays were applied. 

 In several instances, however, the results for the Pickering-sprayed 

 leaves were equal to those for the Bordeaux-sprayed leaves per unit 

 of copper sulphate in the spray. The addition of lead arsenate or 

 rosin-fish-oil soap to the Pickering sprays did not increase the amount 

 of copper which adhered to the leaves. More copper adhered to tke 

 leaves sprayed with standard Bordeaux than to those sprayed with 

 barium water or Burgundy mixture. 



Average results.— -More of the copper of the Pickering (A) than of 

 the Pickering (C) sprays adhered to the leaves. In three of the eight 

 Pickering sprays tested, the copper adhered to the leaves in a higher 

 proportion per copper sulphate content of the spray than the copper 

 of the standard Bordeaux,. 5-5-50. The Bordeaux, 3-1^-50, spray 

 gave higher results than either the Burgundy mixture or barium water. 

 In proportion to the amount of copper sulphate present in the spray, 

 the Burgundy mixture gave the lowest results of all. 



During the season of 1918, the adherence of copper to potato leaves 

 was determined for Pickering (A) spray, containing 0.7 per cent 

 of copper sulphate, for barium-water spray, with the same copper 

 sulphate content, and for Bordeaux, 4-4-50, 4-2-50, and 4-1-50, 

 sprays, each containing 1 per cent of eopper sulphate. The results 

 (Table 5) are very uniform except those for the Bordeaux, 4-1-50, 

 spray, used on plat 5, which gave lower figures than the sprays used 

 on plats 1, 2, 3, 4, and 6. The highest average figure for copper per 

 unit of copper sulphate in the spray was obtained in the case of the 

 Pickering (A) spray with a copper sulphate content of 0.7 per cent, 

 applied to plat 1. In the tests on plats A, C, D, E, and F, in which 

 sprays containing 0.6 per cent of copper sulphate were employed, the 

 amount of copper adhering on the leaves treated with Pickering (C) 

 spray was the same as the amount adhering to those sprayed with 

 Bordeaux. The leaves sprayed with Pickering (A) spray gave 

 slightly lower results and those treated with the barium-water spray, 



