DISEASES OF THE GRAPE 



\V. T. MACOUN, HORTICULTURIST, C. E. F., OTTAWA. 



'I ' J 1 1{ brown rot, downy mildew, gray 

 J. rot, is the rot which up to recent 

 years proved most injurious in Ontario. 

 The general appearance of this rot as it af- 

 fects the fruit has already been noticed. 

 Like the black rot, it affects leaves, stems, 

 and fruit. The disease causes slightly de- 

 pressed patches on the shoots, somewhat 

 like anthracnose, but they are not so deep. 

 The stems, however, are not usually badly 

 afifected, but it is the leaves and fruit which 

 suffer most. I'nlike the black rot, in the 

 case of brown rot once an infection takes 

 place the disease spreads through the tissues 

 of the vine. 



When the leaves are affected they turn 

 pale w^here the disease has been at work, 

 and about this time the under part of the 

 affected leaf becomes downy, indicating the 

 presence of spores and presenting the 

 downy mildew stage of the disease. After 

 this the aft'ected parts of the leaves turn 

 brown. The diseased condition of the 

 fruit is indicated by a brown patch which 

 gradually spreads over the whole grape, 

 which gradually withers. The absence of 

 black pustules readily distinguish this at 

 this stage from the black rot. Sometimes, 

 after the fruit has withered, it becomes cov- 

 ered with a white powdery substance indi- 

 cating the spores, but these do not always 

 develop, much depending on healthy condi- 

 tions. Spray with Bordeaux mixture just 

 before blossoming, after fruit has set. and 

 lo to 14 days later. 



POWDERY MILDEW (Uuci)iula Spiralis). 



This disease does not penetrate into the 

 tissue of the plant as the black and brown 

 rot, but grows upon the surface, n^aking it 

 much easier to treat. Unlike these diseases 

 also, it spreads more rapidly in rather drv 

 weather. The mildew grows on the voung 

 shoots and under surface of the leaves and 



on the fruit, giving them a grayish, pow- 

 dery appearance easily recognized as being 

 caused by the powdery mildew. This dis- 

 ease feeds on the plant by sending small 

 suckers into the plant cells from which it 

 gets food. Spores are produced early in 

 the season and these being scattered about 

 soon infect other leaves or vines and spread 

 the disease. 



A second crop of spores are produced 

 later in the summer and these carry the 

 disease over the winter. These are en- 

 closed in a hard, roundish case which be- 

 comes black during the latter part of the 

 season. 1 his is a very easy disease to treat 

 and yields readily to fungicides. Dry sul- 

 phur and sulphur and water have been 

 found effective, but as this disease often ac- 

 companies other diseases of the grape the 

 sprayings with Bordeaux mixture recom- 

 mended for black and brown rot are pre- 

 ferable and will effectually check it. 



A disease noticed in the vineyards at 

 Winona, Ont., is undoubtedly this species. 

 It causes a withering of the leaves somew'hat 

 like the brown rot, but the fruit is not af- 

 fected nor has the under surface of the leaf 

 the dowmy appearance of the brown rot. 

 The leaves on the vines at Winona had the 

 burnt appearance which is peculiar to many 



The patches on the leaves indicating the 

 disease are large and irregular in outline. 

 The patches become quite dry and will 

 break from the leaf very readily. The 

 spores are borne on the under surface of 

 the leaf on slender filaments and are pro- 

 duced in large numbers during damp 

 weather. This disease lives over the win- 

 ter in the fallen leaves. It has not received 

 much attention, but it weakens the vines and 

 prevents the full development of the fruit. 

 Spraying the vines, as for black rot, should 

 prove quite effectual. 



* Extrart from an address delivered at the last annual convention of the Ontario Fruit Growers' Association. The first portion of this, 

 address will be found in the January issue. 



104 



