Powdery Mildew

Erysiphaceae

Powdery Mildew

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Powdery Mildew is a fast-spreading fungal disease. It is one of the most common and recognisable problems in a garden but doesn't cause significant damage to plants. Unlike other fungal diseases, powdery mildew does not require moisture to infect a plant and is mostly associated with water stress of plants (due to unusually high water content in the spores of the fungi). There are many different species of powdery mildew, and these species tend to have a narrow host range allowing them to infect very few species. This tends to mean that if an apple tree had an infection that it could not transmit it to an oak tree, but it is possible for some plants to be infected with multiple species of powdery mildew at the same time.

Identification

Plants may look like they have been dusted with baby powder or flour. A white, dusty coating on leaves, stems and flowers will be visible, especially on the plant surface.

Growth factors

Poor air circulation, facilitated by low planting distance between plants. High humidity at night followed by low humidity during the day.

Symptoms

Older lesions turn brown and appeared shriveled
White 'powder looking' substance on leaves
Leaf curl
Leaf drop
Infected fruit and flowers are often aborted or malformed

Biological treatment

Milk is probably the most trusted organic method of combating powdery mildew. Dilute it 1:10 and spray onto the plant. Growing resistant cultivars of plants.

Chemical treatment

Fungicides are rarely necessary to manage powdery mildew in a home garden but if you would like protect a special plant choose a fungicide which includes sulfur, lime-sulfur, neem oil, and potassium bicarbonate

Lifecycle

Powdery mildew requires living plant tissue to grow, and either spend the winter as dormant infections on green tissue or as resting structures on plant debris and begin producing spores in the spring. These spores are carried to plants via wind, insects, and splashing water.

Prevention

General hygiene around plants – e.g. Remove, prune out and destroy infected parts, and clearing dead leaves from the base of plants etc. Mulch and water to reduce plant stress but do not fertilize as powdery mildew favours young, succulent growth. Don't water plants from above. Having good airflow through and around the plants. Keeping the plant free of piercing and sucking insects.

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