PICKERING SPRAYS. 17 



Rotten tubers. — Check plat, 3 per cent; plat sprayed with Bordeaux, 

 5-5-50, 4 per cent ; plat sprayed with Bordeaux, 3-3-50, 8 per cent ; 

 plat sprayed with Bordeaux, 3-1^-50, 8 per cent. 



The Bordeaux, 5-5-50, spray gave the lowest average readings for 

 blight. The largest yield of tubers came from the plat sprayed with 

 Bordeaux, 3-1^-50. Apparently the percentage of rotten tubers was 

 not influenced by the spray used. The fact that the plats sprayed 

 with Bordeaux, 3-3-50 and 3-1^-50, were on lower ground than the 

 other two plats, together with the wetness of the season, accounted 

 for the high percentage of rotten tubers found on them. 



REDUCED MILK-OF-LTME SPRAYS IN 1918. 



In 1918 one-acre plats were sprayed with Bordeaux, 4-4-50, 4-2-50, 

 and 4-1-50, to determine the influence of varying amounts of lime 

 on a definite amount of copper. The average results of these tests, 

 which were conducted on the same fields as the Pickering and barium- 

 water tests, appear in Table 3. 



The blight readings are so low that it is impossible to draw a definite 

 conclusion from them. Those for the plats sprayed with Bordeaux, 

 5-5-50 and 4-4-50, are lower than those for the plats sprayed with Bor- 

 deaux, 4-2-50 and 4-1-50. While the Bordeaux, 4-1-50, gave some- 

 what larger yields than the other sprays, the average yields of tubers 

 were practically the same for all the sprayed plats. The slight varia- 

 tion which exists is undoubtedly due to the location of the plats and 

 the fertilizer used rather than to the sprays. 



Adherence of Copper prom Sprays to Leaves. 



The power of various sprays to adhere to potato leaves was tested 

 by Girard (11), who employed standard Bordeaux, Bordeaux made 

 with half the usual amount of lime, Bordeaux made with aluminum 

 sulphate, copper and soda mixture, and copper and acetate of lime 

 mixture. The sprayed plats were subjected to artificial rain for vari- 

 ous periods. The Bordeaux spray made with half the usual amount 

 of lime left the largest amount of copper on the leaves. The addition 

 of sulphate of aluminum was of no value. Butler (7) also concludes 

 that a Bordeaux mixture made with a medium amount of lime has 

 greater adhesive properties than one to which the full amount of lime 

 has been added, and considers the alkaline Bordeaux sprays more 

 adhesive than the acid or neutral Bordeaux sprays. 



Method of estimating copper on leaves. — To determine how much 

 of the copper from the various sprays actually remained on the potato 

 leaves, sets of 50 leaves were picked from the vines on the different 

 plats, the leaves from each plat being placed in separate envelopes. 

 Directly after picking tracings were made of the outlines of the leaves 

 and were later measured with a planimeter to obtain the areas of 



180971°— 20— Bull. 866 3 



