260 



Sanders (G. E.). Arsenate of Lime in Combination with Soluble 

 Sulphur as a Spray Material for the Apple. — Agric. Gaz. Canada, 

 Ottawa, iii, no. 4, April 1916, pp. 305-307. 



During 1915 a large number of spray materials and combinations of 

 them were tested at the Dominion Entomological Laboratory, Bridge- 

 town, N.S. Among these was a sodium sulphur combination con- 

 taining 56 per cent, sodium polysulphide sold under the trade name of 

 " soluble sulphur." It was tested as a summer spray on apples in 

 combination with lead arsenate, with which it almost invariably 

 produced very severe scorching of the foliage. When tested in the 

 laboratory, the addition of acid or hydrogen arsenate of lead to soluble 

 sulphur resulted in the very rapid formation and precipitation of lead 

 sulphide and the consequent formation of sodium arsenate in solution. 

 With the addition of the neutral or tri-plumbic lead arsenate, the 

 formation of lead sulphide and sodium arsenate proceeded much more 

 slowly, and at a diminishing rate. With the addition of arsenate of 

 lime, no change was apparent ; the affinity of calcium for arsenic 

 was so much stronger than that of sodium for arsenic that there was 

 no apparent chemical alteration. As scorching seldom occurs when 

 soluble sulphur is used alone as a spray, while the contrary is the case 

 when it is combined with lead arsenate, it was decided to test the 

 mixture of arsenate of lime and soluble sulphur for its scorching effect. 

 A table of results is given. A mixture of arsenate of lime, f lb. to 

 40 gals., and soluble sulphur, 1 lb. to 40 gals., caused practically no 

 scorching on apple foUage. The season of 1915, on account of the high 

 winds and excessive moisture, gave rise throughout the AnnapoHs 

 Valley to more scorching from lime-sulphur than had previously 

 occurred. FoUage sprayed with lime-sulphur and Bordeaux mixture, 

 even where not scorched, had a dwarfed and pale appearance. With 

 the soluble sulphur, while many leaves were scorched at the tip or edge, 

 the unscorched portions of the leaves were exceptionally dark green 

 and healthy. In one orchard where the mixture of soluble sulphur 

 and arsenate of lead was used without scorching, the filling station was 

 within 25 yards and the material was put on the trees before the change 

 to lead sulphide and sodium arsenate had gone very far. In another 

 orchard the owner sprayed one-half of his tank of soluble sulphur and 

 arsenate of lead as soon as it was mixed, with very little scorching ; 

 a breakdown in the pump caused a delay of 24 hours in using the 

 remainder, with the result that the trees thus sprayed were practically 

 defoliated. A frequent mistake made in using soluble sulphur is to 

 allow the sodium sulphide crystals to come in contact with the air. 

 Contact with oxygen causes a change to sodium thiosulphate, which 

 is valueless as an insecticide or fungicide. This change is indicated 

 by a change in colour from 3^ellowish green to yellowish grey. This 

 evidence, and the fact that there is a marked difference in the action 

 of neutral or tri-plumbic lead arsenate and hydrogen or acid lead 

 arsenate on soluble sulphur, may account for the varied results which 

 have been obtained with this material. 



