16 BULLETIN 866, U. S. DEPARTMENT OE AGRICULTURE. 



case of those sprayed with standard Bordeaux and of from 20 to 50 

 per cent in the ease of the unsprayed plats. The barium-water- 

 sprayed plats yielded from 264 to 303 pounds of tubers, the Bor- 

 deaux-sprayed plats from 247 to 313 pounds, and the check plats 

 215 pounds. 



The application of the 0.6 per cent barium-sulphate spray to 

 smaller plats gave an average blight reading of 1.7 per cent, as com- 

 pared with 0.5 and 1.2 per cent for the Bordeaux, 5-5-50, mixture, 

 and 33 and 45 per cent when no spray was used. The yields of 

 tubers from two rows, each 150 feet long, were: Bordeaux-sprayed 

 plat, 244 pounds; check plat, 235 pounds; barium-water-sprayed plat, 

 241 pounds. 



These results, extending over three seasons, particularly those of 

 1917 and 1918, indicate that a spray made with barium hydrate and 

 containing 0.7 per cent of copper sulphate gives a satisfactory control 

 of blight and the same yield of tubers as a Bordeaux, 5-5-50, con- 

 taining 1.25 per cent of copper sulphate. Plate II, figure 2, shows 

 the protective action given by the barium-water spray in 1918, when 

 the blight was severe. 



In preparing the barium-water spray containing 0.7 per cent of 

 copper sulphate, equal parts of copper sulphate and barium hydrate 

 (2.8 pounds of barium hydrate and 2.8 pounds of copper sulphate to 

 50 gallons) were found to be satisfactory. While such a spray gave 

 good results and reduced the copper sulphate used 44 per cent, the 

 price of barium hydrate is so high that such a spray can not be con- 

 sidered commercially practicable at the present time. If the price 

 of barium hydrate drops, or if barium chlorid, which sells for $75 per 

 ton, can be used, an effective spray may be cheaply prepared. The 

 fact that no residue is left, that the barium hydrate may be added to 

 the spray tank with the water and dissolved there, and that there is 

 reduced wear and tear on apparatus, may induce a trial of this spray, 

 particularly if the yields are shown to be stimulated to a greater 

 extent than with Bordeaux, 5-5-50. 



REDUCED MILK-OF-LIME SPRAYS IN 1917. 



Bordeaux, 3-3-50 and 3-l§— 50, sprays were applied to potatoes 

 during the season of 1917. The reason for reducing the proportion 

 of lime used as milk of lime was to determine its influence on the 

 fungicidal power of the copper and its effect upon the adhesive prop- 

 erties of the spray. 



Blight control. — Check plat, 71 per cent; plat sprayed with Bor- 

 deaux, 5-5-50, 13 per cent; plat sprayed with Bordeaux, 3-3-50, 38 

 per cent; and plat sprayed with Bordeaux, 3-1^-50, 26 per cent. 



Yield. — Check plat, 139 pounds; plat sprayed with Bordeaux, 

 5-5-50, 158 pounds; plat sprayed with Bordeaux, 3-3-50, 148 

 pounds; pint sprayed with Bordeaux, 3-1^-50, 172 pounds. 



