10 Nov., 1917.] Notes on Downy Mildew. 689 



These oil spots, and especially the brown or dead portions of leaf 

 they result in, are not very charactoristic; various causes may lead to 

 quite similar manifestations. Possibly such may have occurred on 

 several previous occasions, but without attracting the attention of vine- 

 growers. The behaviour of the fungus at Fairfield, as described above, 

 is quite in accord with this view. 



The Preponderant Influence of Climate. 



Such freedom from the fungus, almost amounting to immunity, is 

 not peculiar to inland Victoria. It is also a feature of several coun- 

 tries with dry climates — California, for instance. Though Downy 

 Mildew is prevalent to an extraordinary extent in the Eastern States of 

 the North .Vmerioan Union,* so much so that European vines cannot 

 be profitably cultivated, it is practically unknown west of the Rocky 

 Mountains, where climatic conditions are very similar to those of north- 

 ern Victoria. Possibly Mildew may do some damage in the coastal 

 districts of New South "Wales and Queensland, but Victoria and South 

 Australia have far less to fear, at least in normal seasons. _ 



As regards the absence of Downy Mildew from California, Professor 

 Bioletti, in reply to inquiries on the subject, wrote as follows in 1910: — 



This disease iias never been found in California, so far as I am aware. 

 It is reported tliat Dr. FTarkness, of tlie California Academy of Science, once 

 collected a specimen of Peronosporaf on a wild vine in the Sacramento Valley, 

 but the specimen was burnt up in the fire, and in any case it simply proves the 

 extreme rareness of the disease, if it ueciu-s at all here. Anthracnose and Black 

 Rot are also unknown here. Indeed our only serious fungus disease of the vine 

 is the Oidium, and even this, except along the fog belt near the coast, is very 

 easily controlled. 



I think the evidence is conclusive that the reason the serious fungus diseases 

 of the vine do not occur in California is that the climate conditions prevent 

 them. Vines are being continually imported from the eastern States and from 

 Europe, and until lately most of them were not disinfected in any way. It 

 seems certain, therefore", that the spores of all these diseases must have been 

 introduced many times. Our dry summer, four months absolutely without rain, 

 and two or three months with very little rain, sufficiently accounts for th(? 

 difficulty these diseases encounter in becoming established. All I have read of 

 the climate of the main vine-growing regions of Australia shows that it 

 resembles very closely our climate, and if this is true, you need have no fear 

 of the introduction of either Black Eot or Peronospora, 



Likewise in South Africa, as will be seen from the following extract 

 from a reply received from Mr. Watermeyer, manager of the State 

 Vineyard at Constantia : — 



J'lasmopara viticola. — This disease was first found to exist in this country in 

 the Botanic Gardens at Grahamstown, in the Eastern Province, late in January, 

 1907. No clue exists as to how it came, for no one there imported grape vines 

 from Europe. It is not an important grape-growing centre, but there are vine- 

 yards scattered all over the place, and most were found to be infected. Some 

 growers were inclined to the belief that the disease was long established, but had 

 previously been confused with the more common diseases, as Oidium, &c. The 

 disease made its appearance after most favorable weather conditions for its 

 development. Subsequently all districts to which Grahamstown vine 



nurserymen had sent cuttings were inspected, also all the important viticul- 

 tural districts of the colony, in the Western Province. In the latter no infection 

 was found. 



• Downy Slildew l3 in fact indigenous to that part of Norfcli America east of tile Rocky Mountains. 

 It was from liere tiiat it W.1S introduced into Europe in 1879, according to V, V\a\a, Leg Maladies (It la 

 Vigne, p. 77. " In the first year of invasion in France, in 1879, it was not observed until fairly late. Since 

 then the parasit* has appeared as early as the month of May, but never before, since 1879 until 1892. 

 It is well to note this fact, because it should guide for fixing the periods for treatment." 



t The Downy Mildew fungus was formerly Itnown as Peronospora viticola, a name which has since 

 been changed to Ptasmopara viticola. The older name Is still very usually given to it in France. 



