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



occur, and the white down appear, fresh contamination becomes possible 

 unless the tissues have been protected by spraying. Any infection which 

 does occur must incubate before it again reaches the oil-mark stage. 



According to Professor Ravaz, the incubation period has a duration 

 of seven days.* Spraying must not, therefore, be delayed beyond this 

 period, but the nearer its execution to the fatal seventh day the more 

 effectual will its protection prove. 



Another question of considerable importance in deciding the best 

 moment to spray is the receptivity, in other words, the liability of the 

 vine to infection.f Much useful work has recently been done in issuing 

 warnings as to when to spray, based on the co-ordination of meteoro- 

 logical data and receptivity. To the late Cazeaux-Cazalet must be 

 given the credit of being the pioneer in this work, which he first under- 

 took in 1895, in connexion with Black Rot, a totally different fungus. 

 It was found later that similar methods could be applied to Mildew 

 with almost equally satisfactory results. 



In 1898, in collaboration with M. J. Capus, he undertook the warn- 

 ing of vine-growers in the neighbourhood of Cadillac, where he resided, 

 by means of posters, as to the best moment to spray. These warnings 

 proved so valuable that, at the request of vine-growers in neighbouring 

 departments, who subscribed to defray the expense involved, several 

 .stations d'advertissement, or warning stations, were established. This 

 work, which is under the direction of M. J. Capus, has been consider- 

 ably extended during the past few years, with most valuable results. 

 It is highly probable that similar investigations could with advantage 

 be extended to other fungus parasites. 



Without going fully into the rather complex method by which the 

 proper time for warnings is determined, it may be briefly stated that 

 receptivity corresponds with periods when vegetative activity slows 

 down. This is usually due to a spell of cold weather, but, curiously 

 enough, it may also be caused by the soil being too dry. Daily measure- 

 ments of cane growth permit of its being ascertained ; should it corre- 

 spond with a falling barometer, or meteorological stations jiredict rain, 

 spraying is opportune, and warning is given. 



It must be remembered that any leaves and tips of shoots which 

 grow subsequently to a spraying are quite unprotected. In dry weather 

 this is of no consequence, but should moister conditions provide the 

 drops of water necessary for germination, these new growths will become 

 infected; seven days later incubation to the dangerous oil-spot stage 

 will have occurred. Should rain again fall, the white down will appear in 

 abundance, providing countless millions of spores, these will germinate, 

 given a continuance of suitable wet weather — not without — on lower parts 

 of the vine from which the protective spray has been washed by rain. 

 Such defenceless tips are in this way a danger, especially to the young 



• This dxiration of seven days of the incubation of the disease has this year shown no variation. It 

 may thus be considered in practice to be constant. Hsnce, when there are' live germs and a fall of rain 

 takes place, one is forewarned as to wliat will Imppen. Ali there is to do is to take steps to check the 

 invasion which wil' result from that which is already under way. — L. Ravaz, Progres Agricole, 12th 

 August, 1917. 



t In order that vegetable parasites may be able to invade the tissues of the vine two sets of 

 conditions must be fulfilled. 1. .atmospheric conditions such as will permit spore germination. 

 2. Conditions connected with the growth of the vine which place it in a stat^i of receptivity as regards 

 diseases. — J. Capus, in Frogres AgricoU. 26th March. 1911. 



