Powdery mildew

Identifying Features
Infected plants are covered in a dusty, furry-looking greyish-white mould, mainly on the upper surface of the leaves and young shoots.

Treatment
As powdery mildew does not like wet conditions, wetting the leaves reduces the severity of attack. A "wetter", e.g. detergent, has to be added (just a squirt); plain water will just run off the leaves. Weeds can over-winter the fungus, so good garden hygiene is essential. Remove and bin or burn infected leaves, do not compost them.

Prevention
Ensure plants have adequate water, especially those in containers, and apply mulches over moist soil if grown in open soil. Avoid overcrowding plants to give good air circulation and minimise humidity. Don't feed plants too much nitrogen-rich fertiliser because this encourages lush sappy growth which is more susceptible to infection.