DOWNY MILDEW - organic control

Downy mildew is a group of fungal diseases which are common in cool, wet weather. It affects a wide range of vegetables, ornamental plants and fruit trees including grapevines. The fungal spores are spread by wind. First of all small, angular, light yellow or brownish spots appear on the upper surface of leaves. Underneath the leaf these spots produce white fluffy spores.  It causes stunting, wilting, yellowing and the death of seedlings.

The fungal spores cannot germinate in dry conditions and need to be moist for a number of hours in order to germinate so doing everything possible to reduce moisture on the leaves and improve air circulation is important. In areas with high humidity this can be impossible to achieve at certain times of the year.

Suggested Organic Strategies:

• Avoid overhead irrigation.

• Select resistant varieties. Try to remove leaves as soon as they are affected.  Certain vegetables are particularly susceptible including peas, rockmelons and apple cucumbers. Grow plants on a trellis to improve the air circulation around them.

• Spray vulnerable plants regularly with a seaweed based product to build plant vigour.

• Mulching acts as a barrier and helps restrict the spread of fungal spores from the soil onto the plant.

• Dispose of fallen leaves and prunings.

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