Rural School Leaflet 



925 



While the solution of lime is being added to the dilute copper sulfate solu- 

 tion in the sprayer tanlc, the material in the tank should be stirred 

 constantly. The sky-blue bordeaux mixture will result. 



The mixture should now be tested with a few drops of a solution of 

 potassium ferrocyanide. This is made by dissolving crystals of potas- 

 sium ferrocyanide in soft water. Five cents' worth of crystals dissolved 

 in a pint of water will provide enough of the solution to last throughout 

 the season. Should a brown-colored precipitate result when a few drops 

 of this solution are added to the bordeaux mixture, it would indicate that 

 more limewater is needed to neutralize the copper sulfate solution. When 

 sufficient lime is added no precipitate will be formed by the potassium 

 ferrocyanide solution. Bordeaux mixture not properly neutralized will 

 burn the foliage of plants when applied to it. 



POTATO SCAB 



This disease is characterized by a roughened, brown, corky area on the 

 surface of the tuber. While these affected areas extend but slightly below 



Potato tubers badly affected with scab 



the skin, the appearance presented by scabby potatoes renders them less 

 valuable than smooth ones. The yield also from fields where the tubers 

 are badly scabbed is inferior. So that it is desirable, from the grower's 

 point of view, to grow clean potatoes. 



Potato scab is common throughout the United States and Europe where 

 potatoes are grown. The surface of a tuber may be roughened by worms 

 and grubs, but this is unlike the scab. In Europe several organisms are 



