Minnesota Plant Diseases. 



217 



When it is desired to make a barrel of bordeaux mixture, stir 

 the stock solution thoroughly, dip six gallons from each barrel 

 and place in separate tubs. Now dilute each to twenty-five 

 gallons and pour together as already described. The use of 

 the lime is to combine with the copper and form a compound 

 that will not burn the foliage. It also tends to make the fungi- 

 cide adhere to the plant upon which it is sprayed and later dis- 

 solves slowly in rain and dew water to form solutions poisonous 

 to the fungus. To test the mixture to see if all of the copper 

 is combined with the lime, add a drop of potassium ferrocyanide 

 solution. If it changes color upon coming into contact with 

 the bordeaux mixture more lime should be added ; if it does not 



FIG. 107. A barrel pump in action on farm of B. Hoyt, St. Anthony Park, Minn. 



change color the combination is complete. In using bordeaux 

 mixture upon peach or plum foliage it is better to use only four 

 pounds of copper sulphate per barrel instead of six. This is 

 the most common fungicide in use at the present time, but it 

 must be remembered that it stains the foliage and the fruit and 

 should therefore not be used when the fruit is approaching 

 ripening season." Maryland Ex. Sta. Rep. 13: 67-68, 1900. 



The proportion of lime and copper sulphate varies in differ- 

 ent formulae of the bordeaux mixture; six pounds of each is 

 frequently recommended and in weaker solutions six pounds of 



