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 3-1J-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-LIME SPRAYS IN 1918. 
In 19 IS 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 from 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 
