178 



THP: CANADIAN HORTICULTURIST. 



I shall be obliged if you can procure 

 me specimens of the injured sti-awberry 

 bud. 



THE DOWNY MILDEW OF THE GRAPE. 



BT D. W. BBADLE, ST. CATHARINES, OXT. 



It is very probable that many Can- 

 adian vineyardists have suffered more 

 or less from the ravages of this para- 

 site. Possibly they have not known 

 its proper name, nor Vjeen able to dis- 

 tinguish it from other forms of mildew ; 

 bat it is the most common form that 

 infests our grape vines, and usually the 

 most destructive in our climate. 



We shall endeavor to give our read- 

 ers such a description of it that they 

 will have no difficulty in recognizing it, 

 if it should appear ; and what is better, 

 give them a remedy that has been 

 found effectual in Europe, and there- 

 fore worthy of careful trial here. 



Mr. F. Lamson Scribiier, of the 

 United States Department of Agricul- 

 tui'e, has made a very full report on the 

 fungus diseases of the grape vine ; and 

 having been favored with a copy, we 

 shall avail ourselves of his labors to 

 give further publicity to information so 

 valuable to every grower of grapes. 

 "We shall for the present confine our- 

 selves to the Downy Mildew, hoping 

 at some future time to take up the 

 other fungi. The downy mildew is 

 known to botanists by the narne of 

 ITironospora viticola, and attacks our 

 wild as well as our cultivated vines. 

 It preys upon all the growing parts, 

 leaves, young shoots and berries ; and 

 when veiy abundant so weakens the 

 vine as to render it almost or quite 

 worthless. 



The first intimation that the vine- 

 yardist has of its presence is the 

 appearance of small, irregular, light 

 green, or yellowish spots on the upper 

 side of the leaves. On turning up the 

 leaves he will find that there is on the 

 underside, directly beneath the spots 



on the surface, white patches, which 

 have the appearance of mould or mil- 

 dew. These white patches are com- 

 posed of the spore bearing filaments, 

 little threads which have come up 

 through the pores (stomata) of the leaf, 

 have branched and fructified. The 

 spores are borne on the en Is of the 

 branches. Four to even eight of these 

 spore bearing filaments issue from each 

 leaf pore, and it is because they are so 

 numerous that they become visible to- 

 the naked eye. What we see, there- 

 fore, and call mildew, is only the 

 functifying portion of the plant, the 

 vegetative portion is concealed from 

 view in the body of the leaf. 



The vegetative portion is called the 

 "mycelium," and grows between thecells 

 which compose the ti.?sue of the leaf, or 

 of the young shoots, or grapes. This 

 portion has the appearance of minute 

 thx-eads, on which are formed at fre- 

 quent intervals small lateral projec- 

 tions that penetrate the walls of the 

 cells of the vine, absorbing therefrom 

 the nourishment which supports the 

 fungus. It will be seen therefore that 

 the destructive woi-k is done by the 

 portion of the fungus that lies con- 

 cealed from observation in the tissues 

 of the leaf, or berry, or young shoot. 

 The contents of the cells that are thus 

 perforated by these small lateral pro- 

 jections (called '• suckers ") soon turn 

 brown, which causes the discoloration 

 that meets the eye. 



We shall now show how, and under 

 what circumstances or conditions, this 

 mycelium or vegetative portion of the 

 fungus gains entrance into the tissue of 

 the leaf or fruit. It has already been 

 noted that the downy growth which is 

 seen on the underside of the leaves is 

 composed of filaments bearing, on the 

 ends of their branches, spores. These 

 spores are called by botanists Conidia. 

 They are reproductive bodies. When 

 one of these falls on a leaf wet with. 



