Problem focus: Powdery mildew

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As sure as the autumn leaves turn orange and fall, you can be certain of this: the leaves of every courgette, every winter squash, every cucumber in your garden will be covered in a downy white powder right now.

Courgette leaf covered in powdery mildew

Let’s get one thing straight: this is not (probably) your fault. Mildew strikes as soon as the air turns…