PROCEEDINGS, 1918 33 



lime. This mixture was stirred together thoroughly and ap- 

 plied with a dust blower. For the apple this formula was 

 halved, making it two and one half per cent metallic copper 

 and one per cent metallic arsenic. It may be that a stronger 

 dust will be required for the apple. 



Experiments were made to determine the possibility of 

 making the dust by grinding stone lime and copper sulphate 

 crystals. Under some conditions the stone lime was found to 

 extract the water of crystallization from the copper sulphate, 

 and the resulting product was a pure white, fine, powder. This 

 method has not as yet, however, been tried on a practical basis. 



All who used the dust remarked on its mechanical super- 

 iority over any commercial Bordeaux or sulphur dust. Al- 

 though this is true, we can still further improve the dust me- 

 chanically as we used arsenate of lime that occupies 80 cubic 

 inches to the pound in 1918, while in 1919 it is probable that a 

 better dusting arsenate such as is being developed for use on 

 cotton will be used. In the same way the dehydrated copper 

 sulphate used in 1918 passed a screen of 100 meshes to the inch, 

 and the firm that is making our experimental material for 1919 

 is grinding it to pass a screen of 250 meshes to the inch. It may 

 be that the insecticidal and fungicidal action of the dust 

 will be influenced by this fine grinding as well as the mechanical 

 application of the dust. 



Results from Field Tests on Potatoes. 



Various tests were made of the 5-2 dust on potatoes. In 

 all cases late potato blight was effectually controlled. At the 

 Experimental Farm, Fredericton, N. B., the dust plot gave 

 396 bushels of potatoes per acre, while the average of 24 plots 

 that received 4.4.40 Bordeaux was 407 bushels per acre, and 

 the average of the unsprayed plots was 23S frushels per acre. 

 The very poorest type of hand duster on the market was used 

 in applying the dust at Fredericton. At Truro under the di- 

 rection of Prof. W. H. Brittain, the new 5-2 dust was compared 

 with 4.4.40 Bordeaux and the following results obtained: 



5-2 copper dust 744 bushels per acre 



4.4.40 liquid Bordeaux, ars.of lime.. . . 652 bushels per acre 

 unsprayed 550 bushels per acre 



