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



of the field, respectively. Plat 2a, receiving the Pickering spray 

 which contained 0.38 per cent of copper sulphate and was mixed 

 with rosin-iish-oil soap, showed 5 and 3 per cent of blight, and a yield of 

 1,098 pounds, while plat 2, receiving the same spray without the soap, 

 showed 21 and 7 per cent of blight, and a yield of 1,261 pounds. Plat 

 3, receiving Pickering spray with an 0.13 per cent copper sulphate 

 content, showed 13 and 5 per cent of blight, while plat 7 gave 36 and 

 6 per cent for blight. All the Pickering-sprayed plats were next to 

 a check plat, while those receiving the Bordeaux were protected by 

 sprayed plats on each side. 



No rotten tubers were found on any of the plats. As is often the 

 case, some variation occurred in the yields from different portions of 

 the held. The vines of the check plats were not injured by driving 

 through the plats, a factor of some importance in view of the fact 

 that the spray cart was driven twice through some of the sprayed 

 plats and four times through others when each spray was applied. 



It is interesting to note that the average yields of the Pickering- 

 sprayed plats just discussed varied with the percentage of copper 

 sulphate present in the spray. The increased yield of the sprayed 

 vines over that of the unsprayed vines was small, because of the dry 

 weather and the early date at which the vines died. 



The weak Pickering sprays (containing 0.23 per cent of copper 

 sulphate or less) did not give satisfactory blight readings or results 

 for yield. While the 0.64, 0.38, and 0.36 per cent copper sulphate 

 Pickering spra}^s gave little indications of controlling the late blight 

 in the front plats, they showed some control on the rear plats, and 

 all the yields were satisfactory. No differences in the action of the 

 Pickering (A) and Pickering (C) sprays were noticed. The copper in 

 these sprays did not appear to be 12 times as effective as that in 

 the starfdard Bordeaux sprays, but per unit of copper present the 

 Pickering sprays looked promising. It was accordingly decided to 

 try Pickering sprays containing a higher percentage of copper sulphate 

 the following year. 



PICKERING AND BORDEAUX SPRAYS IN 1917. 



The arrangement of the plats adopted in 1916 (p. 8) was varied 

 somewhat in 1917, in that the plats were arranged in triplicate and 

 the various plats receiving the same treatment were placed in three 

 different sections of the field. 



The copper sulphate content of the Pickering sprays tested varied 

 from 0.3 to 0.7 per cent (Table 2). Kosin-fish-oil soap, 2 pounds to 

 50 gallon-, was added to the Pickering (A) spray applied to plat 12, 

 and dry arsenate of lead, 1 pound to 50 gallons, to the Pickering 

 (A) spray applied to plat 13 and to the Pickering (C) spray applied 

 to plat 14. Each of these three sprays contained 0.5 per cent of cop- 



