34 



PLANT DISEASES 



mixture is unsafe, and more lime must be added. If, on 

 the other hand, the blade of the knife remains unchanged, 

 it is safe to conclude that the mixture is as perfect as it can 

 be made. As an additional test, however, some of the 

 mixture may be poured into an old plate or saucer, and 

 while held between the eyes and the light, the breath should 

 be gently blown upon the liquid for at least half a minute. 

 If the mixture is properly made, a thin pellicle, looking 

 like oil on water, will begin to form on the surface of the 

 liquid. If no pellicle forms, more lime should be added.' 



It is very important to remember that air-slacked lime 

 should never be used in the preparation of Bordeaux 

 mixture, since its use results in injury to the foliage. 



The adhesive property of Bordeaux mixture is much 

 increased by adding soft soap in quantity equal to that of 

 the copper sulphate. This is especially necessary when 

 spraying smooth or waxy leaves, the soap increasing the 

 tendency of the liquid to spread instead of forming into 

 large drops, which roll off the surface of the leaf. 



Since the discovery of Bordeaux mixture by Millardet in 

 1885, the general tendency has been to reduce its strength ; 

 and even prepared in the proportions given above, it some- 

 times slightly scorches tender, young foliage. Hence it is 

 advisable to dilute the mixture for spring spraying, using 

 the full strength when the leaves are full grown, and again 

 reducing the strength when spraying young fruit. Apples, 

 pears, and cherries may be sprayed until half grown, when 

 the operation should cease, otherwise the ripe fruit is liable 

 to be spotted. 



With the dilute mixture found to be efficient, the sprayed 

 foliage does not present the appearance of having been 

 whitewashed to the same extent as when a denser mixture 



