The fungal spores will live safely in the winter time inside the buds of the tree or inside little cuts in the bark or branches. If you decide to treat, try one of the eco-friendly fungicides like Neem or the Cornell baking soda mix. It often appears in late spring and early summer. Powdery mildew grows best in conditions where you'd least expect it--instead of a cool, moist environment, powdery mildew prefers warm and dry conditions where there is high humidity combined with moderate temperatures. Different types of powdery mildew affect different types of maple trees. This tree disease is a biotrophic pathogen meaning it can only grow on living tissue so doesn’t kill the host directly. Fortunately a healthy plant can tolerate the damage. But in every case, this disease is not harmful, as the powdery substance merely sits atop leaves. The fungal spores are spread primarily by wind, which can spread them to the rest of the tree or to nearby trees. How Powdery Mildew Spreads. Whenever possible grow ninebarks and other powdery mildew susceptible plants in full or morning sun. Powdery mildew, shown here on a peony, is a fungal disease that attacks many plants including cherry trees. A white powdery substance on the top of the leaf and on the twigs is powdery mildew. Cornell University found baking soda helped suppress powdery mildew. Wind spreads powdery mildew spores from plant to plant, but they only germinate if the leaves they land on are dry. Replied June 29, 2016, 8:31 AM EDT . The white substance is all over the bark of the Bush almost as if someone has painted all of the branches White. These have an unusually high water content, enabling them to infect under drier conditions than most other fungal pathogens. Anonymous Guest. Powdery mildew is caused by a fungus that makes white powdery areas on the leaves of the bay tree. Powdery Mildew Jerzy Opioła / CC BY-SA 4.0. They're most damaging to ninebarks growing in excessive shade, and most active during humid weather with temperatures between 60 and 80 degrees Fahrenheit. Powdery mildew fungi produce microscopic air-borne dispersal spores from the fungal growth on the plant surface. There is no cure for oak powdery mildew, but nurseries routinely have to spray fungicides to prevent the pathogen from stunting the growth of young trees. The roots system is never invaded, and the fungus does not eat away at the leaves. Powdery mildew is a common disease that appears as a white powdery substance on a tree leaf surface. Symptoms: Appearance of white, powdery substance on leaves Causes: The Phyllactinia … Powdery mildew attacks all kinds of landscape plants, including Is this a different form of powdery mildew? The powdery appearance comes from millions of tiny fungal spores, which are spread in air currents to cause new infections. Powdery Mildew.