1906.] 



Spraying Mixtures. 



green with Bordeaux mixture containing 8 lb. of sulphate of 

 copper to 100 gallons of water. The use of lime with Paris 

 green to neutralise its action upon foliage is also commonly 

 recommended ; but this probably decomposes the poison to a 

 much greater extent than does the Bordeaux mixture. 



In consequence of the injurious action of Paris green upon 

 foliage in a tender stage, the use of arsenate of lead is becoming 

 more and more common as a substitute. As this poison is quite 

 harmless to foliage, it is a pity that it cannot be mixed with 

 either of the two ordinary fungicides without losing its efficiency. 

 Dr. Dyer was consulted upon the point, and he stated that if 

 arsenate of lead were mixed with Bordeaux mixture, the lead, 

 by the action of the sulphate of copper, would be converted 

 into ineffective sulphate of lead. Similarly, if potassium sulphide 

 as a fungicide, instead of the Bordeaux mixture, were mixed 

 with arsenate of lead, the result would be the formation of 

 ineffective sulphide of lead and comparatively useless potassium 

 arsenate or potassium sulpharsenate. Again, the mixing of 

 Paris green and potassium sulphide would lead to the conversion 

 of the copper in the former into useless copper sulphide, leaving 

 only the arsenic to be relied on as a poison. In this case appar- 

 ently the fungicide would be the agent rendered ineffective, 

 while the insecticide would still retain considerable virulence. 



For two seasons some extensive spraying experiments have 

 been carried on by the authorities of one of the principal 

 experiment stations in the United States, in which Bordeaux 

 mixture and arsenate of lead have been combined for the pur- 

 poses, mainly, of checking attacks of the Codlin moth cater- 

 pillar and scab in apples and pears. The constituents were 

 10 lb. of copper sulphate, 7 lb. to 10 lb. of lime, and 3 lb. of lead 

 arsenate to 100 gallons of water. The trees were sprayed three 

 times, and the results were decreases of both attacks, but not 

 to a nearly sufficient extent to be regarded as satisfactory. No 

 doubt the explanation is the impairment of the constituents in 

 the way described by Dr. Dyer. As Paris green had proved 

 harmful to foliage, the arsenate of lead was used instead, appar- 

 ently without any consideration of possible decomposition. 

 There is nothing unusual in this neglect of an important con- 

 sideration. In all the numerous reports from American experi- 



