688 Journal of Agriculture, Victoria. [10 Nov., 1917. 



At the commencement of the 1916 seiisoi. there was every reason to fear 

 severe visitations; plentiful germs from hist year, a moist soil during spring, and 

 sufficient rain to permit contamination. In the development of this disease, 

 however, it is not sufficient that a group of favorable conditions should occur, 

 it is essential that every condition should be favorable. It is sufficient that one 

 such should be absent in order for the invasion to fail. Now, in .Tune, 1916, the 

 soil was unusually dry .... hence low receptivity of the vine for the 

 disease. This view receives confirmation from the fact that, at many points, 

 though invasions exist which are at least two or three weeks old, they are 

 discernable in the shape of spots which are only visible by transparence, and 

 which have failed. 



But all districts were not equally fortunate; in certain centres, fortunately 

 very limited, .... the disease has been able to develop very freely, and 

 several invasions have appeared on leaves and bunches. Such contaminations 

 are all distinguished by the fact that at least one heavy fall of storm rain 

 occurred which wetted the soil and left it wet. This rain did not cause con- 

 tamination, but it favoured the appearance of down beneatli the spots, which 

 were only waiting for it, and which in its absence would most probably have 

 continued to remain latent, and would liave failed." 



The origin of tlie 1917 outbreak is and must remain obscure, but 

 tbere can be no doubt tbat the abnormal weather conditions of last 

 summer permitted its development and spread over the large extent of 

 country mentioned above. The weather conditions during the 1916-17 

 summer were altogether abnormal. Hot north winds, usually so common 

 in northern Victoria, were conspicuous by their absence; on the other 

 hand, rains were frequent, the following falls being registered at the 

 Rutherglen Viticultural Station during January and February, 1917: — 

 Sixteen points on 12th January, 42 on 13th, 23 on 21st, 11 on 27th, 

 29 on 31st; 31 on 1st February, 7 on 6th, 22 on 16th, 4 on 18th, 5 on 

 19th, 21 on 20th, 36 on 21st, 7 on 22nd, 34 on 23rd, and 5 on 26th. 

 Heavy night dews, quite unusual in the district, were common, and 

 fogs, most unusual summer visitations on the Murray, occurred on 

 several mornings. In the opinion of the writers, it is solely owing to 

 the unusual amount of moisture present last summer that the fungus 

 was able to show up at all. Whence did it come, and by what means 

 was it introduced? These are questions which can never be answered. 



The grafted resistant rootlings largely imported from France at 

 various times during the past ten years have been suspected as carriers, 

 and it is quite possible that this view is correct. It is equally possible, 

 however, that the fungus was introduced with dried grapes from Spain, 

 Greece, or Turkey, in all of which countries the fungus is abundant. 

 The outbreak in Baron von Mueller's garden, at any rate, did not 

 originate through importation of vines from France.* It is quite 

 probable that the fungus has long been with us, but, owing to climatic 

 conditions, it was not until the very wet summer of 1916-17 that the 

 white, downy efflorescence was able to manifest itself, and without this 

 the fungus cannot be readily identified. Even though infection should 

 take place, and the fungus obtain an entry into the tissues of the plant, 

 its development may only reach the stage characterized by the appear- 

 ance of the yellowish-green spots (becoming brown later) known in 

 Fi-euch as taches d'huih, or " oil spots." Unless sufficient moisture 

 be present, these are unable to sporulate, and there is no appearance on 

 the under surface of the leaf of the characteristic white down, without 

 which the identification of the fungus is only possible by microscopic 

 investigation or artificial incubation in moist media. 



• It is inconceivable that the Baron should have disregarded the stringent legislation then in force 

 against the introduction of vines and tlie heavy penalties it provided. 



