464 journal (if AgricuUure. Victoria. \io July. 191 i. 



naked eye, which occur on the under surface of the leaves, and also on un- 

 ripe berries, attacked by Mildew. In the thickness of the leaves are shown, 

 the oospores, or winter eggs, by which the perpetuation of the disease, from 

 one season to another, is insured. 



It is of interest to note that in the closely allied Potato Blight fungus 

 {PhytophtJiora infestans) this form of reproduction has not as yet been 

 ob.served. 



It was at one time thought that the removal of all leaves and their 

 destruction by hre would, by the elimination of the oospores, constitute 

 a u.seful preventive treatment, which would prevent, or at any rate reduce, 

 the intensity of the first outbreak of the fungus, the following sea.son. 

 Experiments, however, showed the absolute futility of such treatment: 

 The spread of the fungus is so rapid that one single spore, germinating in 

 the spring, would be sufficient to invade a whole district, provided, of" 

 course, that climatic conditions were suitable. 



The conditions necessary for the de\elopment of the fungus are such, 

 fortunately for us, as do not occur in Victoria, at least, not in the districts 

 where the vine is now cultivated. Simultaneous warmth and moisture are 

 indispensable. Such conditions are frequently realized in France. In 

 fact, in Southern Europe generally, where the warm southern wind is 

 charged with moisture, it is the cold north wind which is dry. This is the 

 rever.se of Victorian experience. Our warm wind is the dry north wind, 

 fatal to all forms of fungus life. Even on the coast side of the Dividing 

 Range, dry and warm north winds are frequent, such as are absolutely 

 unknown in Europe. 



In its moisture requirements, Mildew differs altogether from Oidium. 

 The latter can develop if the air be moist or muggy j the former must have 

 drops of water (either dew or rain), at a suitable temperature for the germi- 

 nation of its spores, and this frequently repeated before an outbreak can 

 attain any seriousness. Conditions are frequently suitable for Oidium here, 

 but never for Mildew. The moist warm winds of France, the heavy dews 

 resulting from them, and warm rains of frequent summer storms, provide 

 the drops of water in which Mildew spores readily germinate. The 

 difference between dry Australian heat and the oppressive heat of summer in 

 viticultural Europe, has only to be experienced in order to understand our 

 immunity from similar fungi. 



As regards treatment, the situation of the mycelium in the interior of 

 the tissues, renders direct or curative methods, such as are so successful in 

 the case of Oidium, hopelessly powerless. Preventive measures alone 

 can be of use. Treatment has for its object the prevention of the entrv of 

 the fungus into the tissues of the plant. This can only be achieved bv 

 spraying the whole of the surface, liable to attack, with a substance capable 

 of dissolving in the dew or raindrops, and thus rendering them unfit for the- 

 germination of the fungus spores. The spraving substance must not be too 

 soluble or the first shower of rain would wash it awav. A suitable sub- 

 stance has been found in various copper salts of slight solubility. The- 

 Bordeaux mixture (lime and copper sulphate),- so well known to orchardists, 

 is the oldest and, even now, the standard treatment ; many variations of it 

 are in general use. These will be dealt with in detail later, together with 

 .some other metallic salts, notablv those of mercury, and even of silver, the- 

 most recent innovation. 



The sprav must be fine and e\en. so that no portion of the \ine surface 

 is left untouched by it, sufficiently large to contain a dew or raindrop. 

 Three sprayings are considered necessary in order to insure protection 



