Powdery mildew Erysiphaceae spp.

Look for

Powdery mildew produces a white powdery coating on the surface of plant leaves and fruits and causes plants to become distorted, look unsightly and growth to die back. Affected plants also often display dark brown or bright yellow spots. If it isn't treated, the problem can cause plants to die and crops to become inedible.

Plants affected

• Many garden plants, herbaceous and woody, can be susceptible to powdery mildew. This includes apples, peaches, plums, gooseberries, strawberries rhododendrons, roses, honeysuckle, asters, peas, brassicas and cucumbers, melons and marrows, as well most ornamental plants.

About Powdery mildew

• Powdery mildews are a group of closely related species of fungi that are very similar in appearance, producing a 'powdery' effect on the surfaces of plants.
• The powdery effect is caused by fungal strands throwing out thousands of spores.
• Each species of powdery mildew has a limited host range, and powdery mildew on one species of plant will generally not spread to other unrelated plants.
• All powdery mildews prefer dry conditions on closely spaced plants with poor air circulation and low light.
• Roses growing in dry sheltered areas against walls are prone to powdery mildew.
• Low levels of fungal infection may show no symptoms but develop when conditions are favourable.
• Powdery mildew spores are spread far and wide by the wind.

Treatment

Chemical

Products containing the following chemical ingredients are all effective on Powdery mildew

• Myclobutanil
• Penconazole
• Flutriafol
• Sulphur as a dust, or incorporated in a spray with fatty-acids.

Note: It is important to read manufacturer's instructions for use and the associated safety data information before applying chemical treatments.

Organic

• Prune out infected branches or shoots as soon as you see the first symptoms.
• Do this slowly and put the diseased material into a container to avoid shaking spores on to healthy shoots. Then burn the infected material.
• Some spores of powdery mildew can overwinter on infected material, so remove any sick-looking perennials in the autumn, and clean up thoroughly in the greenhouse with a garden disinfectant.

Prevention

• Ensure plants have adequate water, especially those in containers.
• Keep roots moist by incorporating organic matter in autumn and applying mulches in spring.
• Avoid overcrowding plants or thin out crowded growth, to give good air circulation and minimise humidity.
• Don't give susceptible plants too much nitrogen-rich fertiliser because this encourages sappy growth which is more susceptible to fungi.