ENEMIES OF THE ROSE 91 



remove any disease when once established but it can 

 and does help to prevent the spread of the disease by 

 leaving on the surface of the leaves a thin coating of 

 such poisonous material that spores alighting on it are 

 killed at once. Thus it is obvious that spraying is only 

 valuable as a preventive so long as the material sprayed 

 remains on the leaves, and that after a time it must be 

 renewed if there is much fear of mildew. If the weather 

 is fair, and the dew not unusually heavy, it will be sufficient 

 to spray every fourth day in a garden badly affected with 

 mildew, but, of course, should a sharp shower of rain 

 come on immediately after spraying has been done, its 

 good results will be almost neutralised, and it should be 

 repeated as soon as may be. In using spraying solutions 

 it must be remembered that the strength of the solution 

 used depends on the tenderness or hardness of the foliage. 

 A solution which will do no harm at all to the foliage of 

 a plant growing in full sunlight and air, with leaves 

 hardened by exposure, will shrivel and scorch the leaves 

 of a plant growing in a damp, shady, sheltered position. 

 Mildew is more prevalent in certain seasons than in 

 others, and this is due to the effect of the climate and 

 weather conditions on the foliage of the Roses. Thus 

 in wet years when all foliage is " soft " and tender, 

 having missed the heat of the sun necessary for properly 

 hardening it, the spores of the fungus find an easy prey. 

 This accounts not only for the greater prevalence of 

 mildew in damp summers, but also for the fact that some 

 Roses are more liable to infection than others, and that 

 in general those which are grown under glass are ex- 

 tremely susceptible to mildew. The two periods in 

 which mildew is most likely to attack the plants are, 

 first, in the Spring, when the new young leaves are 

 just full grown, and again in the Autumn, when the 

 plants are making their second growth. The Autumn 

 epidemic is the more dangerous of the two, as it is from 



