Under favourable conditions, powdery mildew can take hold on many common garden plants, both ornamental and edible. Despite looking similar plant to plant, powdery mildews are often host specific, so the disease when seen on a delphinium will be different to that seen on a grape vine for example. Fortunately prevention and control is the same for each.
The disease is easily spotted. White, powdery patches appear most commonly on foliage but can also affect flowers and fruit.
The disease becomes a particular problem during periods of high humidity, especially when soils or container compost is dry.
To reduce the risk of infection, water plants regularly but avoid wetting foliage. Mulching around plant bases will help keep soils moist, reducing the chance of infection.
Affected plant parts can be removed to reduce spread but, being a surface problem, powdery mildew can be easily brought under control with the use of fungicidal sprays.
Plant Rescue Fungus Killer (available as concentrate or as a ready to use spray) can be used on both ornamental and edible plants. For quick control on ornamental plants apply Westland Rose Rescue. Repeat the application two weeks later for total control.
Powdery mildews overwinter on fallen foliage, releasing their spores in spring to start the cycle all over again. Removing fallen leaves from the garden each autumn will help prevent the problem occurring the following year.