A group of fungi appears as a white, often crusty growth on leaves of plants such as grapes, vine crops, lettuce and onion and flowers such as stocks. It can lead to leaf drop, stunted growth, or plant death. Individual species of downy mildew affect specific plants such as brassicas. It can spread rapidly to other related plants but is unlikely to affect unrelated plants.
Young plants such as seedlings may also be affected by some downy mildews and die without other signs of infection. Wet cool weather favours downy mildew, which is usually spread by moisture or wind.
One way of preventing downy mildew is to ensure water doesn’t stay on leaves especially at night, so water your plants via the soil, not the foliage. Good hygiene in the garden including removing dead and diseased foliage, can halt or reduce downy mildew. Selective pruning for good air circulation around the plants and crop rotation are essential.
Downy mildew doesn’t like warm or dry weather, so this is likely to stop the disease. Organic controls include trying 3 parts of milk to 10 parts of water or one tablespoon of baking soda into one litre of water. Mix either option into a spray container and spray the affected foliage weekly.
Other control options include removing early signs of the disease or applying copper. Fungicides such as EarthCare Black Spot & insect spray may be applied to ornamental plants affected by downy mildew and other diseases. Check the label before applying a fungicide to an edible plant. Regular fortnightly applications of Seasol may reduce downy mildew in susceptible plants, as it helps to improve plant health and disease resistance.