Of all the garden diseases, powdery mildew is one of the most widespread and easily recognised. No plants are safe from this disease, but it most commonly affects edible plants including apples, squash, cucumbers and ornamental flowers such as lilac, zinnia, rose and phlox.

Fortunately, powdery mildew will not affect more than one variety of plant at a time; for example, the species of fungus infecting lilacs will not cause powdery mildew on apples. Its spores are spread extensively by the wind.

How to spot powdery mildew

There are several types of powdery mildew fungi, but they all produce similar symptoms on plants. Powdery mildew, which is spread extensively by the wind, causes the surface of the leaves to develop spots or patches of white to greyish talcum powder-like growth.

If the surface of the leaf gets covered with powdery mildew then photosynthesis can be impaired, in which case, look out for distorted, weakened plants. However, powdery mildew also affects the bottom sides of leaves, so remember to check the underside of the plants to catch the disease early.

How to treat powdery mildew

For powdery mildew treatment and control, you can do a number of things.

Firstly, powdery mildew treatment involves removing and destroying all infected plant parts immediately. Powdery mildew grows best in damp or high humidity, so avoid overcrowding plants by pruning and thinning, as this will create good air circulation and minimise humidity. 

It is also a good idea to avoid sheltered spaces, such as walls or fences, as this is where the air is most likely to be still – increasing the likelihood of infection. Instead, we recommend planting seeds in sun-soaked areas of your garden or allotment and avoid overhead watering early in the morning or in the evening.

To remove the spores, wash the leaves thoroughly top and bottom every 1-2 weeks. You can use an appropriate fungicide to treat this disease, but make sure you follow the manufacturer’s instructions.