DISEASES OF CULTIVATED PLANTS 661 



Dust Bordeaux Mixture Formula. The formula given by Mr. 

 W. M. Scott, of this Bureau, for dust Bordeaux mixture and the 

 method of preparation are as follows: 



4 pounds of copper sulphate in 4 gallons of water. 

 4 pounds of lime in 4 gallons of water. 

 60 pounds of slaked lime dust. 



Dissolve the 4 pounds of copper sulphate in 4 gallons of water 

 and slake 4 pounds of lime in 4 gallons of water. When cool pour 

 the two solutions together simultaneously into a tub. Allow the re- 

 sulting precipitate to settle, decant off the liquid, pour the wet mass 

 of material into a double flour bag, and squeeze out as much water as 

 possible. Then spread out the dough-like mass in the sun to dry. 

 After a day's drying it can easily be crumbled into an impalpable 

 powder by crushing with a block of wood or even with the hand. 

 This powder should be screened through a sieve of brass wire having 

 at least 80 meshes to the inch and should then be thoroughly mixed 

 with 60 pounds of slaked lime dust. 



The lime dust is best prepared by slowly sprinkling a small 

 quantity of water over a heap of quicklime, using barely enough 

 water to cause the lime to crumble into a dust. The heat generated 

 will soon drive off the excess of moisture, and the dust should then 

 be passed through a screen of 80 meshes to the- inch. This powder 

 is usually applied by means of a blower. If desired, 4 pounds of sul- 

 phur and 1 pound of Paris green may be added to each 60 pounds 

 of Bordeaux mixture dust. 



Finely powdered copper sulphate, used with lime as a conveyer, 

 is also sometimes applied to plants. When so employed at least 15 

 pounds of slaked lime dust should be used to each pound of copper 

 sulphate, as this will make a pretty strong fungicide. The manufac- 

 turers of dust sprayers have on the market several ready-made prepa- 

 rations. As a rule, these do not contain as much copper sulphate as 

 is recommended in the above formula. 



Value of Dust Sprays. The expense of handling large quan- 

 tities of water in making up the liquid Bordeaux mixture has de- 

 terred many orchardists from using it. In case of certain mountain 

 orchards, it is not practicable to haul the water up the steep hills or 

 mountain sides, nor is it feasible to drive between the tree rows with 

 heavy spraying tanks. There is a very urgent demand, therefore, 

 for successful dry fungicides to be applied without the use of water, 

 as the weight of the material handled is very much reduced. So far, 

 however, in the treatment of apple scab, bitter-rot of the apple, pear 

 leaf-blight, black-rot of the grape, and other fungous diseases requir- 

 ing careful spraying, the dust method may be regarded as still in the 

 experimental stage and of doubtful value. It is not to be compared 

 with properly made Bordeaux mixture applied as a spray in the 

 treatment of these diseases. In the treatment of the codling moth, 

 however, better success has been obtained, and some help may be ex- 

 pected against fungi. Mr. 'Scott's formula is the result of consider- 

 able experimenting, and it is recommended as the best one to use. 

 The writer is not able, however, to recommend dust spraying for 



