270 VEGETABLE GARDENING 



germs will be largely destroyed. It would be a good plan 

 to turn such potatoes occasionally in order to expose them 

 fully to the light. 



Blight of potatoes is a disease which attacks the leaves 

 and stems of potatoes, and sometimes even the tubers are 

 affected. It is most prevalent during moist, warm weather, 

 when sometimes the fungus may be seen as a delicate 

 white mildew on the stems and leaves of the potato vines. 

 In seasons favorable to it, the tops of an entire field may 

 be killed in a few days from the time the disease was first 

 noticed; at other times the tops die so gradually that it 

 is mistaken for natural dying of the vines. Rotting of the 

 tubers often follows the dying of the tops. It has been 

 quite clearly shown that this disease may be kept in check 

 or the trouble entirely prevented by spraying the tops 

 with Bordeaux mixture occasionally. It is, however, 

 somewhat doubtful about the benefits being sufficiently 

 certain in the Northwest to justify the expense; but should 

 this disease become more abundant spraying may prove 

 a paying operation. The cost of treating one acre with 

 the Bordeaux mixture is about $5. There is little use 

 of applying this mixture after the damage from the disease 

 is apparent, for it is a preventive and must be used be- 

 fore the disease is seen. 



Bordeaux mixture is made as follows: Dissolve five 

 pounds of blue vitriol (sulphate of copper) in ten gallons 

 of water in a wooden or earthenware vessel. As this 

 substance dissolves very slowly in cold water and solu- 

 tions of it are very heavy, it is well to suspend it near the 

 top of the water. (It dissolves more quickly in hot water.) 

 In another vessel, slake five pounds of good, fresh quick- 

 lime in ten gallons of water. When the mixture is wanted, 

 pour the blue vitriol and lime slowly at the same time into 



