Rose mildew, the fungus Sphaerotheca pannosa, is one of the many pests of Roses. It attacks plants both in the open air and under glass, covering them with a whitish down, and causing loss of foliage and general ill-health.
Mildew is not usually a source of serious trouble on outdoor Roses when the soil is deeply and well cultivated, and the plants are well fed. Yet unkindly weather may predispose them to attack.
Plants under glass are almost sure to be affected if cold draughts blow on them, and not a few cultivators screw down their ventilators late in summer in order to prevent any risk of an attack from this source.
The favourite remedy for mildew is flowers of sulphur, which is usually dusted on by hand. It is often effectual, especially if applied during an early stage of the attack. Those persons who have many Roses would do well to procure a pair of Malbec bellows from the florist or sundriesman, as with their aid the sulphur (which may with advantage be mixed with one-third of lime) can be thoroughly distributed, both on the under and upper surface of the leaves.
A modern remedy for mildew which is worthy of mention is liver of sulphur (sulphide of potassium). Half an oz. of this ill-smelling substance may be dissolved in 1 1/2 gallons of hot water and sprayed on.