DISEASES DUE TO FUNGI 111 
All infected material should be removed at once and 
burned. Spraying with liver of sulphur and flour paste 
has yielded promising results and vaporizing with 
sulphur is also recommended. 
Powdery Mildew of the Rose.—This disease, caused 
by Spherotheca pannosa (Wallr.) Lév., may cause serious 
trouble under glasshouse conditions. 
On the leaves appear white powdery patches consist- 
ing of innumerable spores (Fig. 31), while dense white 
growths, producing comparatively few spores, develop 
on the fruits and shoots of the plant. These latter 
patches give rise to the perithecia or resistant fruiting 
bodies which carry the disease over the adverse conditions 
of winter. The mildew covers the leaves, especially of 
the young shoots, causing the former to fall, and fre- 
quently deforming the more sappy stems. Usually the 
disease appears in two distinct attacks. One occurs in 
spring, shortly after the leaves have unfolded, while the 
second occurs towards the beginning of July. The 
former attack injures the plant, but does nothing towards 
producing resistant bodies capable of perpetuating the 
disease over the winter. These are, however, produced 
during the second attack, which is therefore the more 
serious. Some roses are more susceptible to mildew than 
others, but in every case moist, crowded conditions are 
most favourable to the disease. Careful attention to 
temperature and ventilation are therefore necessary. 
Dusting with flowers of sulphur at intervals of ten days 
is generally sufficient to control the disease. Liver oi 
sulphur and ammoniacal copper carbonate are also 
effective, while vaporizing sulphur in the houses for two 
hours twice a week is also recommended. 
Rose Leaf Blotch.—This disease, caused by Actinonema 
rose Lib., is second only to powdery mildew in 
destructiveness and frequency. More or less irregular 
purplish spots with a characteristic fringed border are 
