72 



THE DEPARTMENT OF AGRICULTURE. 



TREATMENT WITH CORROSIVE SUBLIMATE. 



This is the most effective treatment and the only satisfactory one against 

 RMzoctonia (black scurf). It may be used for treating potatoes which are affected 

 with scab ; however, the formalin treatment is safer and just as reliable. When it 

 is considered necessary to treat potatoes to prevent both scab and Rhizoctonia, then 

 corrosive sublimate should be used. 



To make corrosive sublimate solution use 4 oz. of the sublimate (mercuric 

 chloride) to each 30 gallons of water and soak potatoes from one and a half to two 

 hours. The corrosive sublimate should be dissolved in hot \vater and an earthen or 

 wooden receptacle used, since it corrodes metal. Potatoes should be treated before 

 cutting. Barrels or vats (Fig. 76) may be used for disinfecting seed-potatoes with 

 this treatment. It is essential that all containers used after treatment be clean and 

 that the same precautions taken as are necessary under the formalin treatment. 



Fig. 77. Sprayer in operation. 



The corrosive-sublimate treatment has the following drawbacks: 



(1.) Corrosive sublimate is a violent poison to human beings and animals if 

 taken internally. It must therefore be used and disposed of with great care. After 

 using, dig a hole where there is no danger of the liquid draining into surface 

 channels, and pour it in. 



(2.) It corrodes metals, including tools, knives, etc., itself becoming weakened. 



(3.) The solution becomes weaker with each lot of potatoes treated. It is 

 generaly recommended to discard it after four lots of potatoes have been immersed; 

 this makes the treatment expensive. (The price of corrosive sublimate in whole- 

 sale quantities is about $3.50 per pound.) 



(4.) Treated potatoes cannot be used for human or stock food. 



SPRAYING. 



Spraying for plant-diseases is preventive only. Once the fungus has obtained 

 entrance, spraying cannot cure the resulting disease; The object of spraying is to 



