PROCEEDINGS, 1918 35 



Action When Applied to Foliage. 



The mechanical mixture of dehydrated copper sulphate 

 dust, hydrated lime, and arsenate of lime, dusts on as a white 

 powder. It sticks very well even if the leaf is dry. The first 

 dew that falls furnishes enough moisture for the reaction be- 

 tween the copper sulphate and the hydrated lime, and the blue 

 Bordeaux is formed just where it is to remain on the dusted 

 surface. A plant freshly dusted will look white but the next 

 morning will sometimes look as blue as though recently drench- 

 ed with Bordeaux. Very efficient work may be done and it is 

 altogether practical to apply the dust during a fog or when the 

 plants are damp from a previous rain, fog or dew. In this way 

 a Bordeaux is made immediately the dust strikes the damp sur- 

 face. 



Storage. 



The completely mixed dust may be stored in fairly open 

 containers such as drums or barrels in a dry atmosphere, for 

 some months without deterioration. 



We believe the most practical method of all on a commer- 

 cial basis, would be for the user of the dust to equip himself 

 with a dust mixer and to buy ingredients separately. The de- 

 hydrated bluestone must be kept in tight containers. The ar- 

 senate of lime and hydrated lime can be shipped and stored in 

 much cheaper containers. In this way the grower can vary 

 his formula as he pleases and as necessity or the plant to be 

 treated dictates, and his container cost would not be so high as 

 if he bought complete mixtures in relatively tight containers. 



Cost. 



In devising the formula for the dust it was the aim to have 

 as much actual metallic copper applied per acre, as would be 

 applied in liquid Bordeaux. Recognizing that there is a great- 

 er waste of material in dusting than in spraying, allowance was 

 made to have a slight excess of copper in the dust, over the 

 liquid. The cost of this dust mixture then, to cover a given 

 area, is the same as required for the materials to liquid spray 

 the same area, plus the cost of the additional copper to over- 

 come wastage, plus the cost of dehydrating the copper sulphate 



