Plant Sanitation. 



226 



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 sulph- 

 ide as a fungicide, instead of the Bordeaux mixture, Avere 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 apparently 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 

 purposes, mainly, of checking attacks of the Codlin moth caterpillar 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 exteut to be regarded as satisfactory. No doubt the explan- 

 ation 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 Avas used 

 instead, apparently without any consideration of possible decomposition. There 

 is nothing unusual in this neglect of an important consideration. In all the 

 numerous reports from American Experiment stations relating to spraying that 

 I have read, not one has entered into the subject of the effect of mixing 

 spraying materials from the point of view of possible decomposition. It is not 

 surprising, then, that in the numerous pamphlets on spraying issued in the 

 United States, chiefly by manufacturers of spraying machines, the point in question 

 is ignored ; and the most incongruous mixtures are commonly to be found among 

 the prescriptions- 

 It appears that a combination of Paris green and Bordeaux mixture 

 in spite of the partial decomposition of the former, remains the most effective 

 combination of an insecticide and a fungicide used at present. For the first appli- 

 cation, just before the buds open, it would be harmless to the trees ; but if 

 applied immediately after the blossom has fallen, when it is most needed for 

 the destruction of the Codlin moth caterpillar, my experience in last season's 

 operations induces me to advise that only 6 oz. instead of the usual 8 oz. per 

 100 gallons should be used, because the foliage is then in a tender stage. The 

 use of 8 oz., with Bordeaux mixture, at this stage, greatly injured the foliage 

 of my apples and plums. That the Paris green was the cause of the injury was 

 proved by precise trials on trees not previously sprayed, a branch on each of 

 several apple trees being treated with Paris green at the rate of 8 oz. to 100 

 gallons, other branches on different trees with Bordeaux and Paris green, and a 

 third set with Bordeaux alone. Each branch was labelled in reference to its 

 treatment, and it was found that the Bordeaux mixture alone had no injurious 



