THE POTATO 183 



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5. Neither the planting of vigorous varieties 

 nor cultivation can be trusted to ward off the 

 disease in a wet season, but spraying with Bor- 

 deaux mixture has been found effective and is now 

 a part of the regular routine of cultivation in humid 

 districts. Even in dry seasons when no disease is 

 apparent the treatment is found to be beneficial, 

 producing a longer period of growth and an in- 

 creased yield. This is so generally recognized that 

 spraying has become general in several potato- 

 growing districts, whatever the season promises 

 to be. As the disease does not as a rule make 

 much headway before the end of July, spraying is 

 seldom wanted for the first early sorts, the leaves 

 of which will be dying down before any great harm 

 is done. 



** Bordeaux mixture may be prepared as follows : 



Sulphate of copper or bluestone 12 lbs. 



Freshly burnt quicklime 8 lbs. 



Water 75 to 100 gals. 



"In order to obtain good results from Bordeaux 

 mixture, careful attention must be given (1) to the 

 materials employed, and (2) to the preparation. 



"1. Materials: Copper sulphate of 98 per 

 cent, purity should be obtained, 'Agricultural' 

 copper sulphate, which usually contains iron sul- 

 phate, must be avoided. Iron sulphate or cop- 

 peras is valueless for this purpose. 



"An easy test for the presence of iron in the 

 copper sulphate is to dissolve a little in water and 

 add ammonia with constant stirring until a deep, 

 blue liquid forms; any quantity of brown flocks 

 floating about in this blue liquid indicates the 

 presence of so much iron that the material should 

 be subjected to a proper analysis previous to use. 



