Powdery mildew: This is a common fungal disease for courgettes, especially in dry conditions when plants are under stress. You will see white, powdery patches of fungus on leaves, stems and, in severe cases, the fruits.
Remedy: Mulching and watering reduces water stress and helps make plants less prone to infection. Promptly removing any infected shoots will reduce subsequent infection. There are no chemicals to treat powdery mildew, but you can use plant and fish oils, or sulphur dust as a preventative.
No fruit, or fruit rotting when very small: This is a physiological problem, caused by the growing conditions, not a pest or disease. It is a problem when the weather in early summer is cool and this causes inadequate pollination.
Remedy: This is usually a temporary problem, and once the weather starts to improve, so will pollination. You can try to hand-pollinate plants yourself by removing a male flower (male flowers don’t have a swelling at their base) and brushing the central parts against the centre of a female flower (female flowers have a swelling at the base – this is the beginning of the fruit). But this is a bit of a hassle, and normally the plant will correct this problem itself.
Grey mould: This is a problem normally in wet conditions, and is usually worse on weak or damaged plants. The mould normally enters through a wound but, under the right conditions, even healthy plants will be infected. You will see fuzzy grey mould on affected buds, leaves, flowers or fruit. Infected plant parts eventually shrivel and die.
Remedy: Hygiene is very important in preventing the spread of grey mould. If you see grey mould, remove the infected material and destroy. Grey mould is encouraged by overcrowding, so make sure you plant your courgettes at the appropriate distance apart. No fungicides are approved for use by amateur gardeners against grey mould. Products containing plant and fish oil blends may be used, but are unlikely to have much impact.
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