I04 



The Canadian Horticulturist. 



TREATMENT OF GRAPE MILDEWS. 



HERE are two kinds of mildew which interfere with the prosperity 

 of the vineyardist, and, while we in Ontario have had comparative 

 immunity from the Downy mildew which is the most destructive 

 form, yet the Powdery mildew, which is only too familiar to us, is 

 rapidly gaining ground in our vineyards. While it does not come 

 within the scope of a horticultural journal like this to enter into any 

 scientific description of these fungi, it is yet necessary for us to be able 

 to distinguish the one from the other. 



The Downy mildezv (Peronospora viticola), which in the south is very common 

 and destructive, appears to be slowly invading our territory. When it affects the 

 berry, it is spoken of as the Grey Rot, and at a later stage as the Brown Rot ; as 

 seen upon the leaves in the summer season, this mildew has the appearance of 

 a shining white powder, on the under side, and by the aid of the microscope this 

 is seen to consist of summer spores growing in thousands upon little branches 

 which spring up through the breathing spores, or stomata, of the leaves, 

 (Fig. 28). There are also parts which correspond to roots, and which draw 

 nutriment for this fungus from the cells of the leaf, and sooner or later cause it 

 to die and fall to the ground. The little summer spores are produced in count- 

 less numbers, and may be carried from one affected leaf over the whole vineyard. 



Late in the fall the winter spores are 

 formed, which live inside the leaf through 

 the winter, and in the spring are just in the 

 right condition to propagate the disease. 

 The dry leaves are blown about in every 

 direction, and, when disintegrated by the 

 spring rains, set free hosts of spores to settle i^'^ 

 upon the young foliage. These quickly send 

 down minute suckers to absorb the nutri- 

 ment which was intended for the develop- 

 ment of the leaf itself. 



The Poivdery 7nildew (Uncinula spira- 

 lis) which is so common a pest in our Cana- 

 dian vineyards, differs from the one just des- 

 cribed, first, in appearing upon the upper 

 side of the leaves and berries as a dirty 

 white coating, from which it takes its name ; 

 and, second, that it is wholly external and 

 does not penetrate to the interior of the 

 leaf or fruit; and, third, the winter spores are 

 not within the leaf but upon its surface, 



where they may be easily discerned when 



Fig. 28. — Spore-Producing Branches 

 OF Downy Mildew. 



