How to recognise it
A white, powdery, fungal coating on leaves (generally the top surface), stems, buds and occasionally flowers and fruits. It initially appears as small, off-white patches on leaves, which then spread. The leaves may yellow, wilt and drop early and the entire plant may wilt due to a severe infection.
Why it’s a problem
As well as being unsightly, powdery mildews can weaken the plant, causing wilting and early leaf drop.
Where you are likely to find it
There are many different species of powdery mildew which affect many different plants. Infections are usually most severe in dry, warm climates, particularly where there is reduced air flow around plants (eg where they are grouped closely together).
How to prevent it
Good hygiene will help prevent the spread of powdery mildew. Ensure that hands and equipment (especially secateurs) are cleaned between different plants and clear debris at the end of the season to remove any overwintering fungal spores.
Ensure that plants are kept well watered in dry periods (mulching well early in the season will also help) and that the flow of air around them is not restricted (eg by crowded herbaceous growth which could be thinned out, other plants or hedging).
Some cultivars have been developed with a level of resistance to mildews.
How to get rid of it
Fungicides, including sulphur (although this can damage some plants), can be effective against powdery mildew and should be applied at least fortnightly in dry, summer periods.
You can remove the infected plant parts (particularly leaves) however you must be careful when doing this, so you don’t shower neighbouring leaves with fungal spores. An easy way around this is to carefully place a bag over the leaf to be removed before pruning it, so any spores fall into the bag. Any diseased cuttings should be destroyed (eg burned) and not put on the garden compost heap.
Is it good for anything?!
Other useful information
There are many different specific powdery mildew diseases. We have further details about: