The Bordeaux Mixture. - It is an interesting fact pertaining to the now general use of the sulphate of copper for controlling the fungous diseases of cultivated plants that its value for such use was discovered by chance (155. Evolution of Spraying). In south France near the city of Bordeaux, grape-vines near the highway suffered loss by stealing of the ripe fruit. The practice soon became quite general of sprinkling the foliage near the highway with a solution of milk of lime and sulphate of copper. This colored the leaves and gave rise to the belief that the fruit was poisoned. It was soon noticed that the vines thus treated were relatively free from mildew. Since that time the use of what became known as the Bordeaux mixture has rapidly extended to all parts of the earth occupied by civilized man, and is used for controlling nearly all fungous diseases of the orchard, vineyard, small fruits, flowers, and garden crops. The most approved formula for making the Bordeaux mixture at this time is to dissolve four pounds of copper sulphate in two gallons of hot water in a wooden pail with constant stirring. When dissolved pour the solution into the barrel or tank to be used, adding five gallons of hot water. Then slake four pounds of fresh lump lime thoroughly and strain the milk through a brass strainer - with not less than thirty meshes to an inch - and while hot pour it into the tank with hot water enough to make a total of fifty gallons.
In using, the solution must be kept stirred to prevent clogging the sprayer and to secure an even distribution. Some successful users throw away what is left and clean the tank and pipes and make a fresh supply at each successive spraying. But others - including the professional sprayers - keep on hand a stock solution of the sulphate and slaked and strained lime in separate barrels.
For the stock solution one pound of sulphate is dissolved in one gallon of hot water. In this proportion a barrel of the solution will keep through the season if well covered, and the same is true of the milk of lime in a separate barrel. In use the lime and sulphate are mixed in the proportions wanted for varied uses as noted in succeeding sections.