418 Jijiiriial of Agnenlturi--, Victoriii. [10 July, 1917. 



la Giroday found later (about 1895) that dilute sulphuric acid alone 

 was capable of giving good results. 



All authorities are in agreement as to the immeuse^ superiority of 

 preventive winter treatment over summer, or curative applications, 

 made whilst the vine is in active growth. Prevention isi better than 

 cure. In connexion with this fungus, the old adage is peculiarly ap- 

 propriate. The winter swab is undoubtedly the standard treatment. 

 Spring or summer ap])lication& can only be looked upon as supplemen- 

 tary, they may do son.e good, but too much must not be expected of them. 

 Summer treatment may be held over for the present, though it niay be 

 briefly explained that it includes dusting with dry mixtures of lime and 

 .sulphur and spraying with Bordeaux mixture, or other copper-contain- 

 ing sprays ; the last-named seem to be the more effectual. 



The Winter Swab. 



From the above it is evident that both concentrated iron sulphate 

 solution, and 10 per cent, sulphuric acid, are effectual destroyers of the 

 resting stages of Black Spot. Each, however, has its disclavantages. 

 The first must be very strong (about 50 per cent.) in order to be effec- 

 tual ; at this strength it must be kept warm and applied warm to avoid 

 crystallization, and this is inconvenient in practice. Ten per cent, 

 sulphuric acid is very corrosive, and requires careful handling. It has 

 a rather drastic action on the vine, sometimes causing the wood to split 

 in an alarming manner, especially if dry, windy weather follows its 

 application. A compromise, in the shape of a combination of both of 

 the above formulae, would seem to be the best way out of the diffi- 

 culty. In France, very varied formulaj are given by different authori- 

 ties, the amount of sulphate of iron varying from 10 per cent, to 50 per 

 cent., and that of sulphuric acid from 1 per cent, to 10 per cent. It 

 would appear that the greater the sulphuric acid strength, the less iron 

 sulphate is needed, and rice versa. The action of iron sulphate is some- 

 what obscure; this salt is a poor fungicide as compared with copper 

 sulphate. Nevertheless, the latter seems quite useless, at least against 

 the resting stage of the fungus; it would, no doubt, be mere active 

 when spore production has commenced in spring. 



Taking all these facts into consideration, we are led to recommend 

 the following as the most generally satisfactory formula : — 



Iron sulphate, 35 lbs. 



Sulphuric acid, 3 to 5 lbs. 



Water, 10 gallons. 

 For convenience in measuring the acid, it mav be mentioned that 

 ar ordinary wine bottle (reputed quart size) holds 54 oz., or nearly 

 3i lbs. of sulphuric acid. 



The solution, being very corrosive, must not be placed in rec°'>tacl6s 

 made of any metal other than lead; it can be most conveniently handled 

 in wooden vessels, preferably painted or paraffined inside and out, and 

 with hoops tarred or paraffined before being driven on. To make it, 

 place the iron sulphate crystals in the tub, pour the sulphuric acid 

 over them, add the water, and stir occasionally until dissolved; if hot 

 water be used, solution will be more rapid. 



Another way of making it is by tying the sulphate of iron in a 

 piece of hessian or bag2;ing, and suspending it in the upper part cf the 

 water in which it ia to be dissolved, the sulphuric acid being added after 



