xvi PLANT DISEASES 



AMERICAN GOOSEBERRY MILDEW 



{Sphaerotheca mars-uvae, Schw.) 



In the first edition of this book, this disease was briefly 

 alluded to, as proving injurious to European varieties of 

 gooseberries in the United States. In the second edition 

 its presence in Ireland was recorded, where it had proved 

 destructive in some districts, and appeared to be extend- 

 ing its area. We have now to record its occurrence in 

 England; it has also appeared in several European 

 countries. This disease is much more injurious than the 

 European gooseberry mildew, described at p. 95 of this 

 book, inasmuch as it attacks the fruit and renders it 

 useless, whereas the European mildew does not pass on 

 to the fruit. It first appears on the leaves and young 

 shoots as a white mildew, resembling in appearance the 

 hop mildew, to which it is allied. At a later stage the 

 fruit is attacked. The white mildew film gradually 

 becomes thicker in substance, and changes to a dingy 

 brown colour, and can be peeled off the fruit as a thin 

 felt-like layer. Numerous summer spores are produced 

 during the white stage; these are scattered by various 

 means and infect other bushes. At a later stage con- 

 siderable numbers of the winter form of fruit, under 

 the form of minute black points, are produced on 

 the matted, felt-like mycelium. These fruits remain in a 

 stationary condition during the winter, and start the infec- 

 tion the following spring. Experiments extending over 

 the last fifteen years have clearly proved that, by the usual 

 methods of spraying, this disease can be held in check. 

 Nevertheless, now that the disease has appeared in Eng- 



