THE PRINCIPLES OF DISEASE CONTROL 91 



Copper sulfate. Copper sulfate is frequently employed as a 

 wash for dormant trees and also for disinfecting seed of grains 

 which may be contaminated by adherent fungous spores. The 

 solution may be prepared as suggested under Bordeaux mixture. 

 When diluted, it should consist of : 



Copper sulfate I lb. 



Water . 15 gal. 



It is seldom that one would desire to apply copper sulfate 

 to the growing tree, on account of its injurious action upon the 

 leaves, but occasionally it has been employed at a strength of 

 1 pound to 100, gallons of water. 



Corrosive sublimate. Bichloride of mercury, commonly known 

 as corrosive sublimate, is an unusually strong poison for man as 

 well as for animals ; at the same time it is a very effective disin- 

 fectant and is very generally employed for potato scab. The 

 solution consists of : 



Corrosive sublimate ... . . 2 oz. 



Water .... . . . 15 gal. 



This is practically a solution of 1-1000 by weight, a strength com- 

 monly employed by physicians for disinfecting purposes. Seed 

 potatoes which may have come in contact with the scab fungus 

 should be soaked for one and a half hours in a solution of the 

 strength indicated. This solution may also be used as an anti- 

 septic dressing for wounds, especially after pruning. It should be 

 made in a wooden or earthenware vessel, since it attacks metallic 

 substances vigorously. 



Formalin. Formaldehyde vapor dissolved in water to give a 

 solution which is ordinarily 40 per cent bears generally the com- 

 mercial name formalin. It is like the last-mentioned fungicide, 

 also a strong disinfectant, and is used very extensively for treating 

 seed potatoes and seed oats and wheat. It should be employed of 

 the following strength : 



Formalin 1 oz. 



Water 2 gal. 



Since formalin is a chemical which may be handled more con- 

 veniently and with less danger than corrosive sublimate, it must be 

 given the preference. 



