230 The Canadian Horticulturist. 



MILDEW OF THE GRAPE. 



HE disease, particularly referred to in the following, is known 

 among viticulturists as " downy mildew," " brown " or "gray 

 rot " of the grape, and to scientists as Peronospora viticola. and 

 was very severe last year in many grape growing districts. It 

 has been particularly destructive in the Eastern and Central 

 States, and also in Western Ontario. Last year it was pre- 

 valent in vineyards in the Province of Quebec, and also in the Ottawa Valley. ^ 



As a rule it is first noticed on the fruit when about half formed, presenting 

 a downy and frosted appearance, which gives place to a grayish-brown in the 

 later stages. The berries shrivel and fall to the ground when slightly shaken. 

 Beginning with one or two varieties in the vineyard, the disease if allowed to run 

 its course will spread rapidly, attacking other kinds, which were at first entirely 

 exempt. 



It usually affects the leaves and wood later in the season, sometimes in the 

 case of early varieties after the fruit has been gathered. This stage of the disease 

 was prominent as affecting the Roger Hybrids in the Experimental Farm vine- 

 yard last season. 



At first it is seen on the upper surface of the leaf shown in brown spots, 

 while the lower surface presents the frosted appearance resembling that form of 

 the disease affecting the fruit. This particular leaf form is not easily detected on 

 grapes having the thick pubescent leaves characteristic of the Concord family. 



TREATMENT. 



Carbonate of copper 2 oz. 



Ammonia i >^ pints 



Water 25 gals. 



As soon as the mildew made its appearance last year on our vines they were 

 thoroughly sprayed with the above mixture. Two applications and the removal 

 of all diseased berries had the effect of checking the spread of the malady, but at 

 the same time demonstrated — when compared with the results of my former ex- 

 periments — that the proper line of treatment leading to complete success, lies in 

 the early application of the remedy. 



The following is the course of treatment planned for the vineyard of the Ex- 

 perimental Farm this season : 



1. All prunings, leaves, etc., to be carefully burned. 



2. When vines are uncovered spray them — including the posts and trellises — 

 with a simple solution of copper sulphate (blue vitriol) i lb, dissolved in 1 5 gal- 

 lons of water. 



3. Spray with the ammoniacal copper carbonatei using the formula already 

 given soon after the fruit sets ; make two or three additional applications at in- 

 tervals of ten days or two weeks, as the necessity of the case seem to demand. 



4. Remove and destroy diseased parts of the fruit and foliage. 



Bulletin 10, Experimental Farm, Ottawa. 



