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Powdery Mildew


Powdery Mildew

Usually appear in

Spring to Autumn.

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Caused By:-     Various Fungal spores


Although several Powdery Mildew fungi are non specific, often different powdery mildew fungi tend to infect either plants in the same family or only one species of plant. Some powdery mildew occur on top of the leaves, stem, flowers and fruit and some above and below the leaves and around the stems.
Some Genera causing Powdery Mildew are Erysiphe, Microsphaera, Phyllactinia, and Podosphaera.
All powdery mildew fungi require living plant tissue to infect and grow. Powdery mildew fungi grows as a thin layers of mycelium on and in the surface of the affected plants. The symptoms are usually very similar regardless of the specie of fungus and host plant, which are whitish/grey fungal mycelium and fruiting bodies, carrying spores on leaf surfaces, shoots, flowers and fruits.
New soft growth, especially those created by high nitrogen feeding, is usually affected first later spreading to older growth.
Growth may be dwarfed, distorted, die and drop from the plant earlier than healthy leaves.
Two types of spores that spreads the disease is usually produced. The first type is unenclosed spores, usually grey in colour, that spread the disease in the summer and enclosed spores, usually black, the enclosure which protect the spores over the winter until it breaks down and releases the spores in the Spring. Wind and water splashes carries powdery mildew spores to new hosts.
Moderate temperatures of 21°C, high humidity and shady conditions with low airflow are the most favourable for Powdery Mildew development, but most Powdery Mildew do not require the presence of water to infect a host. The fungus overwinters as growth in buds, on fallen leaves or as spores inside a enclosure which eventually breaks down to release the spores.
The severity of the disease depends on several factors such as variety of the host plant, age and condition of the plant, and is especially severe in warm, dry climates. This is because the fungus does not need the presence of water on the leaf surface to infect it. However, 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.
Picture by Howard F. Schwartz, Colorado State University,
See also these other Powdery Mildews Apple, Begonia, Hydrangea, Oak, Pansy, Pea, Phlox, Quince, Rose.
See also Downy Mildews Brassica, Downy, Hebe, Lettuce, Onion, Pansy, Pea.
See also other Mildews American Gooseberry, European Gooseberry, Gooseberry.


The best method of control is prevention therefore good hygiene and cultural practices are essential to avoid this disease.
Raking up fallen leaves, placing plants in full sun with pruning that allows good airflow through the plant, Winter tar, oil or fungicide wash and pruning out severely infected branches and burning them will all help in preventing attack from these fungi.
Fungicides are often ineffective and special fungicides will have to be used.
A weekly spray of milk at a concentration of at least 10% (1 part milk to 9 parts water) is said to significantly reduced the severity of powdery mildew infection.
Weekly preventative sprays of baking soda( 1 tablespoon of baking soda a few drops of washing up liquid to 1 Gallon of water) makes an inexpensive control for powdery mildew on plants. Once the infection has taken hold baking soda offers only minimal benefits.
Some plants can be burnt by the baking soda therefore test before use on specific plants.
Spraying 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.
Mulching the plants should help in preventing many Powdery Mildews which prefer dry conditions.

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