802 



Bordeaux Mixture. 



[JAN., 



Of what value these improvements from the chemical point of 

 view will prove in practical spraying against fungus pests 

 has yet to be ascertained, for there is probably a biological 

 side to the question of the action of fungicides. For the 

 reason given below I consider that the practical fruit-grower 

 should continue to make his Bordeaux mixture with equal 

 parts of copper sulphate and lime, i.e., with a considerable 

 excess of lime. So far as I have seen, if Bordeaux mixture is 

 made (like that made from the Woburn Bordeaux Paste) with 

 practically no excess of lime,* it either does not adhere so 

 well to the parts sprayed, or more quickly washes off under 

 the action of rain or dew, and consequently does not protect 

 the plant for long from fungus pests. In 1908 I compared 

 the adhesive power of Bordeaux mixture made with "milk- 

 of-lime," i.e., a mixture containing an excess of lime, with 

 that of the mixture made with "lime-water," i.e., a mixture 

 containing no excess of lime. The two mixtures were tested 

 in potato spraying on a fairly large scale. It was found that 

 the latter mixture was washed off comparatively soon by the 

 rain, and in consequence of this the "blight" (Phytophthora 

 infestans) was not kept in check to anything like the same 

 extent as where the haulm had been sprayed with the Bor- 

 deaux mixture made with "milk-of-lime." Experiments were 

 made during 1909 with Bordeaux mixture made from the 

 Woburn Bordeaux paste, both on apple trees and on potato 

 haulm. In both cases all visible traces of the spray had dis- 

 appeared several weeks before the spray from Bordeaux 

 mixture made with " milk-of-lirne " had become washed off. 

 In the case of apple foliage, the "scab" fungus began to 

 grow on the leaves, showing that there was a complete 

 absence there of any fungicide. The same experience has 

 been reported to me by a fruit-grower in East Kent, who for 

 several seasons past has been successful in keeping a large 

 acreage of apples practically free from "scab" by spray- 

 ing with home-made Bordeaux mixture, although previously 

 this pest had been very prevalent. This grower writes as 

 follows : " I experimented with the Bordeaux paste and used it 



* Bordeaux mixture containing no excess of lime can be easily made by using just 

 enough lime, in the form of " lime-water," to precipitate all the copper (see Woburn 

 Exper. fit -tut Farm, 8th Report, p. 9 (1908). 



