Powdery mildew is easy to identify and is one of the oldest fungal diseases known to man. The infection will cause a white to grey powdery fungal growth on the leaves, stems and heads of plants. Interestingly, although the signs are similar on all types of plants, the disease is species specific, so an infection on your roses, for example, will not affect your grapes. The good news is that powdery mildew is rarely fatal for the plant, but can lead to leaves yellowing, curling and eventually turning brown and falling off the stems. Flower buds can also be affected, reducing the yields of vegetables and fruits.
The disease is more prevalent in high humidity and warm to moderate weather, on dry leaves and in low light – so at just about any time during the warmer seasons.
If you’re growing plants prone to powdery mildew, like pumpkins, melons, squashes, cucumbers, peas, beans and tomatoes, here are a few things to consider:
- Look for disease-resistant varieties to plant.
- Provide enough space around plants for good air circulation.
- Place them in a position where they will get at least six hours of sun a day and minimal shade. The fungus does not like direct sunlight.
- New growth will be more susceptible, but the condition often starts on mature plants.
- Use a slow-release fertiliser and avoid over fertilisation.
Powdery mildew can’t grow on wet leaves. The need for early detection is vital in controlling the problem. Commercial products on the market are often aimed at preventing the problem from occurring, or at least for treating upon early detection. Use a fungicide specific to powdery mildew and use it exactly as per the instructions. If the problem gets out of hand, remove and destroy all the infected plants. Don’t add them to the compost heap as the spores can be passed onto other plants by air movement.