Garden Diseases

Powdery Mildew

Of all the garden diseases powdery mildew is one of the most widespread and easily recognized. 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

There are several types of powdery mildew fungi but they all produce similar symptoms on plants. The surface of the leaves develops spots or patches of white to greyish talcum powder-like growth. You can see the disease easily on the top of leaves. However, powdery mildew also affects the bottom sides of leaves, so remember to check the underside of the plants to catch the disease early.

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.

 

How to treat

For powdery mildew treatment and prevention you can do a number of things: Firstly, remove and destroy all infected plant parts immediately. Don’t put infected plants on your compost.

Powdery mildew grows best in dampness or high humidity so avoid overcrowding plants by pruning and thinning as this will create good air circulation and minimise humidity. 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. Make sure you follow the manufacturer’s instructions.


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