H'yl INSECTICIDES, FXTNGICIDES, AND WEED KILLKES. 



of 5 per cent of sulphate of magnesia and 1 per cent carbolic acid. 

 Although of an elViciency which is highly contested, followers of this 

 practice include responsible experts (^larek, Pagnoul). 



Peronospora viticola, De Bary (mildew of the vine). — Solutions of 

 magnesia sulphate act on the spores of this fungus, but they are not so 

 poisonous as the salts of copper, so the experiments of Sbrozzi on 

 diseased vines gave only very imperfect results. 



53. Magnesium Bisulphite, MgH.,(S03),. — Preparation.— By 

 treating magnesia stirred up in water with sulphurous acid. 



Use. — Botrytia cinerea, Monilia fruticjena, Coniotlujvium diplodi- 

 ella. — Istvanffi found that bisulphite of magnesia had the same action 

 on spores of these fungi as calcium bisulphite, of which an O'O per cent 

 solution acted in the same conditions eighteen times more energeti- 

 cally than a 10 per cent, solution of bouillie bordelaise. He advises the 

 use of a 0"4-0"5 per cent solution of bisulphite of lime or magnesium 

 to combat these fungi, a dose which can be increased to 1 per cent 

 without drawback. 



54. Silicates of Magnesia. — Occurrence. — Two natural silicates 

 may be used against plant diseases; they are steatite, 3Si022Mg0.2, 

 talc, SSiO.^iMgO. These two compounds are widely distributed in 

 nature. 



Properties. — The silicates of magnesia are neutral, inactive bodies 

 insoluble in water. Owing to their fine division [and unctuosity] 

 steatite and talc show a very great adherence to plants. 



Use. — Their extreme fineness and lightness render steatite and talc 

 highly appreciated for assuring to anticryptogamic substances a perfect 

 distribution on diseased plants. These two silicates, therefore, enter 

 into the composition of a large number of powders. Their role is to 

 dilute the active principle. 



Uncinula Americana, How. — One of the chief uses of talc is in the 

 PowfZre/o?tto used against oidiura and consisting of talc 90 per cent, 

 sulphur 10 per cent. 



Perojiospora viticola, De By. — Steatite and talc are the most 

 appropriate substances for the prepai^ation of copper powders used to 

 combat mildew. Sulpho-steatite consists of talc and blue vitriol. The 

 powder Fostit made at Antwerp contains 90 per cent of talc and 10 

 per cent of blue vitriol. These two preparations are those most used, 

 as owing to their lightness they penetrate vines better than any other 

 preparation. 



Botrytis cinerea, Pers. (grey rot of the vine). — The powder which 

 has been most successful against this disease is that used by Dr. 

 Baretto, on the advice of the Baron de Chefdebien. It consists of talc 

 92 per cent, sulphate of alumina 3 per cent, sulphate of lime 4 per 

 cent, green vitriol 1 per cent. This mixture should be applied by 

 copious dusting before and after flowering if it be desired to remove 

 mould ; if it be desired to arrest the grey rot it is necessary to apply 

 this treatment every ten to twelve days after the disease appears. 



According to recent trials talc does not play any active role in this 

 preparation ; the active agent is the sulphate of alumina ; the sporicidic 

 property in this special case is superior to that of blue vitriol. But 



