CONTROLLING VINE DISEASES 



281 



Controlling Tuber Diseases. The diseases transmitted on the 

 exterior -of the tuber are treated by soaking in some disinfectant that 

 will destroy the disease, but not the eyes of the potato. Common 

 scab and rhizoctonia (Fig. 110) are the most common diseases 

 transmitted on the tuber. The common treatment for scab is to soak 

 tubers in formalin solution (one pint to 30 gallons of water) for 

 one hour. This, however, will not kill rhizoctonia. Black leg is 

 killed by corrosive sublimate solution one ounce to seven gallons of 

 water, soaking the seed for ten minutes. 



FIG. 111. A power sprayer, that will spray seven rows at one time. 



As the latter treatment will also kill scab, it is advisable to use 

 the corrosive sublimate treatment, thus treating against both diseases 

 at once. 



Controlling Vine Diseases. Late blight is the principal vine 

 disease to be contended with. This is controlled by the use of 

 Bordeaux spray mixture (Fig. 111). Late blight (Fig. 112) is a 

 fungous disease, growing on the outside of the leaves, and is killed 

 by a very weak solution of copper sulfate, which, however, does not 

 injure the leaf if properly neutralized by lime. 



The strength of the Bordeaux mixture is expressed as 3350 or 



