PLANT DISEASES. 247 



upon the timeliness and the thoroughness with which 

 the work is done. Spraying is most profitable and 

 successful for the diseases that infest their hosts at par- 

 ticular periods. 



Preparation of Fungicides. The chemical sub- 

 stances most often used as fungicides are copper sul- 

 phate or bluestone, sulphur, corrosive sublimate and 

 formalin. The most generally useful fungicide is 

 Bordeaux mixture. To prepare 50 gallons of usual 

 strength, 5 pounds of bluestone and 5 pounds of 

 freshly slaked stone lime are dissolved separately, each 

 in 25 gallons of water. The two solutions are poured 

 together while they are stirred thoroughly. The lime 

 neutralizes the caustic action of the copper sulphate, 

 which has a tendency to injure leaves and fruit. 



Sulphur Mixtures. Two sulphur mixtures are im- 

 portant. One is the boiled lime-sulphur wash, gener- 

 ally used against San Jose scale, but equally effective in 

 destroying fungus spores. This wash is too strong 

 to be used on any but dormant plants. Fifteen pounds 

 of sulphur and 20 pounds of lime are required to 

 make 50 gallons, and the mixture is boiled for an 

 hour. Quite different in composition and. use is the 

 self-boiled lime-sulphur mixture. It requires 8 pounds 

 of sulphur and 8 pounds of lime for 50 gallons, and 

 it does not require boiling. The lime is slaked with 

 cold water, and the sulphur added as the slaking be- 

 gins; the heat thus developed causes as much of the 

 sulphur as is needful to go into solution. This mix- 

 ture is even safer to use on foliage and fruit than the 

 Bordeaux mixture. 



Corrosive sublimate and formalin are merely diluted 

 with water before using. Their most important use is 

 for disinfecting seed, soil, wounds or implements. 



EXERCISE. If any of the members of the class have ever seen 

 fungicides made and applied, he prepared to tell the rest of the 

 class the process and the crop or crops which were sprayed. 



