10 Ji-LY, 1918. 1 Xofes on Vine Black Spot. , 421 



(h) Spring and suinmer sprayings with copper mixtures, to 

 prevent the spread of the fungus, resulting from the 

 development of any wintering forms which may have 

 escaped destruction by swabbing. 



The Winter Swab. 



The following is the formula now recommended as most generally 

 satisfactory : — 



35 lbs. Iron Sulphate. 

 8 lbs. Sulphuric Acid. 

 10 gallons Water. 



For convenience in measuring the acid, it may be mentioned that an 

 ordinary wine bottle (reputed quart size) holds 54 ozs., or nearly 3^ lbs. 

 of sulphuric acid. 



To make the solution, place the iron sulphate crystals in a wooden 

 tub or barrel, pour the sulphuric acid over them, add the water (pre- 

 ferably hot), taking care to avoid splashes of the acid; stir occasionally 

 until dissolved. If the iron sulphate is dissolved first, and the acid 

 added subseqiiSntly, this should be poured in, in a thin stream, with 

 constant stirring to avoid splashes. 



It will be observed that the solution now recommended contains 

 somewhat more acid than that suggested a year ago. Several considera- 

 tions have lead to this alteration, mainly the extreme virulence of the 

 disease last season, and the great abundance of sclerotia, or wintering 

 forms, left by it. Though the 3 to 5 per cent, acid previously recom- 

 mended is capable of destroying the sclerotia, the higher percentage of 

 acid should necessarily prove even more fatal to them; the extra cost 

 per acre is trifling, and if an error is made, it is well that it should be 

 in the direction of extra efficiency.* 



Some growers may even prefer to bring the acid strength up to 

 10 per cent. Though such does not appear to be necessary, there is no 

 serious objection to doing so. In France, damage, in the shape of 

 splitting of the wood of the vine, has sometimes been reported after 

 swabbing with 10 per cent, sulphuric acid (without iron sulphate). In 

 Mildura last season, some growers who used up to 10 per cent, acid, 

 with iron sulphate, found that no damage was done to the wood. 

 Obviously, a couple per cent, of acid more or less will neither make nor 

 mar the swab. 



Thoroughness of application is probably of greater importance than 

 actual percentage of acid ; any sclerotia missed by the swab will naturally 

 survive, irrespective of acid strength. 



Simplification by discarding the iron sulphate and swabbing with 

 10 per cent, sulphuric acid 'only, is sometimes suggested; this is not 

 recommended, the complete formula given above is certainly preferable. 



Though the mnnner in which the iron snlphnte acts is not very clear 

 (see previous article), its value in increasing the efficiency of the swab 

 seems undeniable; it is corroborated both by French and Australian 



• It is worthy of note thit French authorities h v^ for rnvny year^ been content w'th :i sohition 

 cont ining \--> pr rent, arid, 3 p t rent, beng rar 'ly re onim-rdr-d Qn'te rerentiy, however, 

 inrr'-a-^od .^tre-inth i- b^ing ^idvi od— the latest formnli p ib ished going as liigh as 8 per cnt. 

 (Drgrnl'y, Prnnri>s Aijricnlf 1017). 



W'd 'ly (lifP.ir nt fo-inulfp I'avc b en bte'y '■e^ommendrd v>rvin<? from 50 per rent, iron sulphate, 

 with 2 p:r cent, sulphuric acid, to 5 per cent, iron sulph..te w th 10 per cent, sulphuric acid. 



