1907.] American Gooseberry Mildew. 



545 



and the procedure to be adopted in cases where the disease 

 is suspected. 



Description and Life History. — The disease usually first 

 appears as a delicate white mildew on the expanding leaf -buds, 

 extending later to the young wood and fruit. The mildew 

 generally becomes visible during the latter half of May or the 

 first half of June, when it appears in the form of " glistening 

 frost-like spots " on the fruit on the lower part of the bush, 

 where there is usually dense shade. It then spreads to 

 the leaves and tender shoots. In its earlier stages it has a 

 cobwebby appearance, which soon becomes white and powdery 

 owing to the development of the light conidial spores.* 



During the summer and autumn great numbers of spores are 

 produced, which are conveyed from infected to healthy shoots 

 or adjoining bushes by wind, rain, insects, &c. The patches of 

 mildew gradually change from white to a dingy brown colour, 

 and at a later stage become densely studded with the winter 

 fruit, which appears in the form of very minute black dots. 

 The spores contained in the winter form of fruit germinate the 

 following spring and give rise to the white summer mildew. 



In this country the fungus appears to be mostly confined 

 to the tips of the shoots, which, when badly affected, present 

 a brown and shrivelled appearance, somewhat similar to that 

 produced by an attack of " green fly." On such shoots, if 

 carefully examined, especially with the aid of a magnifying 

 glass, the brownish patches of mildew studded with black winter 

 fruit can be readily seen. 



Precautions. — All nurserymen and market-gardeners who 

 purchase gooseberry bushes or Ribes aureum (the stock upon 

 which the standard gooseberry bush is worked) should observe 

 the following precautions : — 



(1) Only to purchase from those growers or dealers who 

 are prepared to offer a guarantee that the plants they are 

 selling are of their own growing, and that no case of American 

 gooseberry mildew has ever appeared in their gardens or in 

 the immediate neighbourhood, and that the said plants have 

 not been near any gooseberry plants recently brought on to 

 the seller's premises. 



* Reference should be made to the illustrations given in the May issue of the 

 Journal. 



(2579) 2 M 



