These appear on leaves and stems as a white powdery substance that spreads rapidly throughout your plants, causing leaves to curl and the overall health and production of the plant to suffer. The highly-prevalent foliar diseases around at the moment are downyand powdery mildew that affect the cucumbers, squash and zucchini families. Lots of our summer plants are being affected by fungal diseases this month - these include tomatoes, potatoes, zucchini, squash, cucumbers and capsicums to name a few. Share this article facebook copy link twitter linkedin reddit email