46 



The white form appears as glistening white patches o$ 

 mildew on the berries, shoots and under-sides of the young 

 leaves (see Figs. 1, 2 and 3).* This stage may occur at 

 any time from May to October, and is consequently often 

 referred to as the summer stage. Whilst in this form the 

 mildew produces vast quantities of minute spores (conidia) 

 which are readily spread, and, germinating at once, produce 

 fresh spots of mildew on any young growth on which they 

 may alight. In this way the mildew is very rapidly distri- 

 buted, especially in warm and moist weather. Suckers or 

 soft, quick-growing shoots on bushes which have been highly 

 manured or grown upon deep porous soils containing an 

 abundance of moisture are particularly liable to be attacked. 



The brown stage is a subsequent development of the white 

 stage, and it occurs abundantly on the shoots and berries 

 and, less often, on the leaves (see Figs. 3 and 4). It takes the 

 form of a thin felt which can be peeled off easily with a knife 

 or with the finger nail. The felt consists of fine threads of 

 fungus mycelium, and in it will be found embedded minute 

 spore-cases known as perithecia, which contain the resting or 

 winter-spores. The perithecia- are just visible to the naked eye 

 as minute black specks (see Fig. 5). 



As in the case of other mildew fungi, these bodies are 

 produced in late summer and autumn, and normally remain 

 dormant till spring, when they discharge their spores and 

 bring about the infection of the new foliage. It is known, 

 however, that a certain number of spores are discharged 

 from the perithecia the same season that they are produced. 

 Notwithstanding this autumn spore-discharge, it is of the> 

 utmost importance that as many perithecia as possible should 

 be destroyed by the practice known as " tipping," or cutting 

 away of affected shoots, in September. There is, however, 

 another point of importance to remember in connection with 

 tipping, namely, that many of the perithecia do not remain 

 attached to the brown felty mycelium till spring, but fall 

 out on the ground during the autumn and winter. The 

 necessity, therefore, of early tipping as insisted upon in the 

 paragraph on " Tipping " is clear. 



Measures of Control. There are two principal lines of 

 treatment against American Gooseberry Mildew : (1) spraying, 

 to prevent and to destroy the white or summer stage ; and (2) tip- 

 ping, to eliminate the brown stage with its resting: spores. In 

 addition, it need hardly be said, that all possible measures 

 should be taken to prevent the disease from gaining access to 

 areas not affected. 



* This serves to distinguish it from the very much less serious disease 

 known as European Gooseberry Mildew, in which almost invariably the 

 leaves only, and chiefly the old ones, are affected. (See Leaflet No. 52.) 



