10 Sept., 1918. 



Downy Mildew. 



571 



It will suffice to recall here that 2 per cent. Bordeaux mixture 

 (2 lbs, copper sulphate to 10 gallons of water, with enough lime of good 

 quality to neutralize)' is the standard spray; its wetting or spreading 

 power can, with advantage, be increased by the addition of casein at the 

 rate of 1 oz. to 10 gallons of spray mixture.* 



How often must vines be sprayed to insure safety? The answer 

 depends on weather conditions. Given those which prevail in France 

 during spring and summer, the frequent sprayings common in that 

 country would, of course, he needed here; fortunately, our climate 

 diifers altogether from that of France. In normal seasons we have 

 even drier conditions than prevail in Algeria. It is, therefore, probable 

 that mildew control will be at least as easy here as it is in Northern 

 Africa, where the disease is not feared to nearly the extent that it is in 

 France. Indeed, our experience of it in so abnormally wet a season 

 us the last is most reassuring; it encourages the hope that one spraying 



in the early part of the season (before 

 Christmas) will save the grape crop. A 

 second spraying in late January or early 

 February will probably be required, in 

 most seasons, to protect the foliage, thus 

 allowing the grapes to ripen properly, and 

 to accumulate the reserves essential for the 

 following season. Its utility will deipend 

 much on the prevalence of the fungus during 

 the spring. 



Save in altogether abnormal seasons, 

 these two sprayings should suffice. We 

 must not forget, though, that we grow the 

 same vines as in France, and we have the 

 same disease to deal with. Should we, 

 therefore, have the misfortune to experience 

 the same kind of weather, similar treatment 

 to that needed in France can alone protect 

 our vines. 



Fig. 3 



Macroconidium (abovo) resulting 

 germination of oospore (below). The 

 Macroconidium is itself almost ready 

 for germination ; its contents liavo 



The First Spring Spraying. 



divided into numcrons Zoopores. After What our viue-growers particularly want 



Ravaz. (Highly magnified.) ,, ., • ,-, j. < 



to know just now is the most opportune 

 moment for the first spray, a question which it is not nearly so easy to 

 definitely answer as might at first appear. The chief object of the 

 present note is to endeavour to throw some light on the subject. 



Spraying being essentially preventive, it must precede infection; 

 once the fungus has penetrated the tissues, any fungicide application is 

 powerless so far as that particular invasion is concerned, f " Too 

 late" spells disaster; it is, however, also possible to be too early. Any 



* For 50 gallons of spray mixture take 5 oz. Casein ; mix (dry) with three or four handfuls of fresh 

 slaked lime in powder ; make into a smooth paste with a little water ; when quite smooth add water to 

 make half a gallon ; pour through a sieve into the 50 gallons of Bordeaux mixture. 



Casein may also be dissolved in 10 per cent, washing soda solution (1 lb. to 1 gallon). 



Casein must only be added to alkaline " Bordeaux." If it fails to redden phcnolphthalein test paper, 

 add more lime until the paper changes colour. 



The use of casein is to be recomir ended for the first spraying; it increases bunch protection by 

 enabling these to be more thoroughly wetted. 



t The spray material remaining on the vinos will, of course, serve to combat the ne.xt invasion 

 which, after about seven days (the period of incubation) will result from the previous one if weather 

 conditions render it possible. 



