2OO 



Commercial Gardening- 



is checked, and they usually soon die. In the case of old leaves, only the 

 parts attacked by the fungus turn brown and die, the remainder usually 

 undergoing no change. Young shoots that are attacked turn black and 

 die, as does also the inflorescence. Berries soon crack and become distorted 

 (fig. 391). 



As the fungus is quite superficial, it can readily be reached by fungicides, 

 and should cause but little trouble if promptly attacked. Spraying at 

 intervals ot three days with a solution of sulphide of potassium is the most 

 certain remedy. Flowers of sulphur dredged or blown over the affected 

 parts is also efficient, but it is more difficult to cover every part with a dry 



powder than with a sub- 

 stance in solution. 



The common practice of 

 placing sulphur on the hot 

 pipes is a practice that can- 

 not be recommended. It is 

 risky, and if the tempera- 

 ture exceeds a certain limit, 

 scorching of the foliage is 

 the result. 



Grape Mildew (Plasmo- 

 paraviticola). This disease 

 (fig. 392) is said to have 

 been introduced into Europe 

 from the United States, 

 where it is very destructive 

 both to cultivated and native 

 wild vines. Every part of 

 the plant is attacked, al- 

 though the foliage suffers 

 most, where its presence is 

 first indicated by the ap- 

 pearance of sickly yellowish- 

 green patches on the upper 

 surface of the leaf, corres- 

 ponding in position with 

 patches of a very delicate 

 greyish mildew on the under 

 surface of the leaf. Under 

 favourable weather condi- 

 tions that is dull, warm, 

 and moist the patches of 

 mildew rapidly increase in size, and often cover the greater portion, or the 

 whole, of the leaf. After this stage is reached, the leaf turns yellow, then 

 brown, and falls. Tendrils and flowers are as promptly killed. Even if 

 the berries are not attacked they do not mature properly, owing to the loss 



Fig. 392. -Vine Mildew (Plaamopara (Peronospom) viticola) 



1, Summer form of fungus on grapes (natural size). 2, Summer 

 fruit (magnified 80). 3, 4, 5, Detached spores of summer fruit (mag- 

 nified 350). 6, Winter form of fruit formed on the mycelium of the 

 fungus present in the tissues of the diseased portion of the plant 

 (magnified 350). 



