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Rose Powdery Mildew


Rose Powdery Mildew

Usually appear in

Spring to Autumn

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Caused By:-     The Fungus Podosphaera(Sphaerotheca) pannosa


Rose Powdery Mildew is caused by the fungus Podosphaera(Sphaerotheca) pannosa. It is only one of many powdery mildews most of which are host specific to certain from cereals and grasses, to fruit trees, and broad-leaved shade trees.
The majority of the growth of most powdery mildews is found on the plant surface. The fungus sends feeding structures into the surface cells, greatly reducing the vigour of the plant.
The disease is usually observed on the upper sides of the leaves with a whitish fungal growth developing on the leaf surfaces in patches which eventually coalesce to cover the leaves, stems or buds. The infected areas dies or may become soggy.
The fungi produce microscopic air-borne dispersal spores from the fungal growth on the plant surface.
The white powdery mildew mould start off on the leaves and soon spreads to buds and other young rose shoots. The affected foliage curls up and eventually falls off if not treated. Flower buds may not open properly, and if they do, will be severely affected.
This fungus is more prevalent in dry warm climates, but if the relative humidity is high the problem will be worse, but it does not tend occur when leaf surfaces are wet. Therefore, Crowded plantings where air circulation is poor damp and in shaded areas makes the problem worse. Young growth usually is more susceptible than older plant tissues.
Powdery mildews either spend the winter as dormant infections on green tissues, or as resting structures on fallen leaves which then release spores the following spring.
Picture by Clemson University - USDA Cooperative Extension Slide Series,
See also these other Powdery Mildews Begonia, Hydrangea, Oak, Pansy, Pea, Phlox, Powdery, Quince.
See also Downy Mildews Brassica, Downy, Hebe, Lettuce, Onion, Pansy, Pea.
See also other Mildews American Gooseberry, European Gooseberry, Gooseberry.


Improve circulation by pruning and keep the tree growing healthily with adequate water and mulching to conserve water as dry conditions exacerbate the conditions.
Mulching around the rose root system in early spring will help prevent water stresswhich will lead to less chance of getting this fungus.
A winter tar or oil wash may help as this fungus overwinters in the buds as well.
Spraying, every two weeks, with a mixture of baking soda(sodium bicarbonate) or potassium bicarbonate combined with a lightweight horticultural oil is said to cure and prevent the problem.
Succulent tissues are more susceptible to infection therefor high nitrogen feeding may exacerbate the condition.
Once the disease is a problem, avoid late summer applications of nitrogen fertiliser. You can also grow mildew resistant Rose varieties instead of more susceptible Roses.

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