CHAPTER XVIII 

 INSECTICIDES AND FUNGICIDES (continued) 



COPPER FUNGICIDES (Reports, VIII, 5 ; XI, i; XIV, App.) 



OF the various compounds of copper used as fungicides, the 

 chief ones are the basic sulphates and the basic carbonates. 

 The former are the active substances in Bordeaux mixture, the 

 latter in soda Bordeaux, more recently termed Burgundy 

 mixture. 



(i) Bordeaux Mixture 



This has been in use since 1882, the recognition of its value 

 as a fungicide being due to accident. It had been the practice 

 in the vineyards in the neighbourhood of Bordeaux to sprinkle 

 those vines which were near a road with verdigris, in order to 

 give them the appearance of having been poisoned, and so to 

 prevent depredations. A mixture of lime and copper sulphate 

 was soon substituted for the verdigris, being cheaper, and, when 

 the downey mildew of America (Peronospora viticola) made its 

 appearance in Europe, it was noticed (1882) that those vines 

 which had received the copper dressing were those which kept 

 their leaves longest, and were least affected by the disease. 



The mixture in general use in this country is made by adding 

 1-6 parts by weight of quick lime, previously slaked and made 

 into a milk, to 1-6 parts of crystallised copper sulphate, dissolved 

 in 100 parts of water (16 Ibs. to 100 gallons). This is known in 

 America as the " normal " or " 1-6 " mixture. Occasionally, 

 stronger or weaker mixtures are used, and al;o the proportion of 

 lime to sulphate is varied. For complete decomposition, the 

 crystallised sulphate requires only one-fifth of its weight of pure 

 lime, therefore the lime used in practice is always in consid- 

 erable excess, even when a liberal allowance is made for 

 impurities in it. 



It is somewhat remarkable that, in spite of the large amount 

 of work which had been done on Bordeaux spraying, both in 

 France and America, no attempt had been made to obtain 

 information on the point of most fundamental importance, 



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