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



treated with Pickering sprays containing less than 0.4 per cent of 

 copper sulphate yielded less than the corresponding Bordeaux- 

 Sprayed plats but more than the check plats. The yield of tubers 

 from the sprayed plats showed an increase of from 30 to 40 per 

 cent over that from the unsprayed plats. 



A high proportion of rotten tubers was found on all the plats. 

 This was due principally to the wet weather, but partially to the 

 late start made in applying the sprays. The percentage of rotten 

 tubers from the various plats is too variable to permit of any definite 

 conclusions. The tubers from the check plats showed no more rot 

 than those from the sprayed plats. Barrels of potatoes from several 

 of the plats treated with Pickering and Bordeaux sprays, as well as 

 from the check plats, were stored in a potato cellar until February, 

 1918, when the tubers were sorted. The percentage of rot found 

 among the potatoes from the various plats was very uniform. 



In 1917 the blight was severe, and the land used for the experi- 

 ments was uneven, which gave some of the plats a decided advantage 

 over others. The results showed that a Pickering spray containing 

 0.7 per cent of copper sulphate is in all respects as efficient as a 

 Bordeaux, 5-5-50, containing 1.25 per cent of copper sulphate. 

 No differences were noted in the relative efficiency of the Pickering 

 (A) and (C) sprays. While these sprays were not shown to be 12 

 times as effective as standard Bordeaux, the indications were that 

 they were more efficient per unit of copper in the solution used than 

 the Bordeaux mixture. 



PICKERING AND BORDEAUX SPRAYS IN 1918. 



Series 1. — Tests with Pickering (A) spray, containing 0.7 per cent 

 of copper sulphate, were made on two farms in the vicinity of Presque 

 Isle, as well as on the farm used hi 1916 and 1917. Each spray was 

 applied five times to acre plats, using a Watson sprayer, two nozzles per 

 row, hi two instances, and a new single-nozzle sprayer in the other. 

 Twice during the season the vines were double sprayed. 



The blight, while widespread in July, and threatening to do as 

 much damage as in the previous season, was stopped by the dry 

 weather during August. The blight readings on the vines, made by 

 three individuals working independently, were low, 2 per cent or less, 

 for the Pickering- and Bordeaux-sprayed plats. The check plats 

 showed from 20 to 50 per cent of blight. Evidently, then, the 

 Pickering sprays applied in 1918 checked the blight as effectively 

 as did the Bordeaux mixture. 



The yield results on two of the farms varied greatly, according to the 

 location of the plats, because of an uneven distribution of manure 

 and fertilizer over the fields. On the farm previously used for the 



