Powdery Mildew
Disease · Commonly affects: courgettes, roses, apples, pumpkins, squashes, peas, gooseberries, phlox
Powdery mildew is a common fungal disease that forms a pale coating over leaves, shoots and sometimes fruit. It is familiar in UK gardens and allotments, particularly in dry spells with humid air. Although it rarely kills established plants outright, it weakens them, spoils crops and makes ornamental plants look tired and untidy.
How to identify it
The first signs are small, dusty white or pale grey patches, commonly 2-10 mm wide, on upper leaf surfaces. These enlarge and merge into a flour-like coating. Young leaves may curl, pucker or become distorted, while older leaves can turn yellow or brown around the patches. On courgettes, the white markings of some varieties can be mistaken for mildew, so look for a wipeable powdery surface and spreading patches on several leaves.
Damage
A heavy coating shades the leaf and reduces photosynthesis, slowing growth and reducing flowering or cropping. Repeated infection can cause leaves to yellow, dry and drop early. Courgettes and other cucurbits may produce fewer or poorer fruit, while roses and apples can lose vigour. Stressed plants are less able to cope with hot, dry weather.
Prevention
Keep roots evenly supplied with water, as drought-stressed plants are particularly vulnerable, but water the soil rather than leaves. Mulch with organic matter to conserve moisture and improve soil structure. Space plants for airflow, prune congested growth where suitable, and avoid overfeeding with nitrogen-rich feeds. Choose resistant varieties when available. Clear fallen leaves and old infected growth at the end of the season to reduce carry-over.
How to manage it
Remove badly affected leaves or shoot tips as soon as practical and place them in household waste rather than leaving them beside plants. Water deeply during dry spells so roots remain steady in moisture. Improve airflow by gently tying in, thinning or pruning overcrowded growth, without stripping plants bare. Continue harvesting courgettes and fruit regularly. Healthy established plants often outgrow mild infection once weather conditions become less favourable.
Powdery Mildew: frequently asked questions
How do I identify powdery mildew?
The first signs are small, dusty white or pale grey patches, commonly 2-10 mm wide, on upper leaf surfaces.
How do I prevent powdery mildew?
Keep roots evenly supplied with water, as drought-stressed plants are particularly vulnerable, but water the soil rather than leaves.
How do I get rid of powdery mildew?
Remove badly affected leaves or shoot tips as soon as practical and place them in household waste rather than leaving them beside plants.
General guidance for UK home gardens and allotments, focused on prevention and non-chemical control. For a confirmed diagnosis, the RHS or a local garden centre can help. Page updated 19 Sep 2026.