White spots (powder) on zucchini plants: how to treat powdery mildew?

Powdery mildew can weaken courgette plants and reduce their crop. Check the leaves regularly so you notice changes early. An established infection cannot always be eliminated completely.

Recognising powdery mildew

Look for a white, powdery fungal coating on leaves and sometimes stems. Affected leaves may turn yellow, become distorted and dry out. Check whether patches are spreading: some courgette varieties naturally have silvery markings on their leaves.

Give plants good growing conditions

Follow the recommended plant spacing and allow air to circulate. Check soil moisture and avoid both drought and waterlogging. Water at soil level where possible. Remove dead plant debris and choose less susceptible varieties when available.

Nettle feed is not guaranteed protection against powdery mildew. Feed according to the crop's needs and avoid unnecessary overfeeding.

What to do when mildew appears

Carefully remove badly affected leaves with clean tools without stripping the whole plant. Watch the remaining leaves and new growth. Treatment will not restore tissue that is already damaged.

Home mixtures containing milk, garlic, bicarbonate or soap do not guarantee a cure and can damage leaves if used incorrectly. Avoid improvised daily spray mixtures. If you consider a crop protection product, check that it is suitable for courgettes and follow its label, including application instructions and harvest interval.

Check cucumbers, pumpkins and melons too. They are also members of the cucurbit family and can be affected by powdery mildew.