How to prevent powdery mildew in the garden

    Are you always fighting with powdery mildew on plants? It shows up about mid-summer to fall when warm days are followed by cool nights. The high humidity at night favors the fungus spores. Does this mean stop watering at night? No, because powdery mildew requires no water to germinate and infect a leaf.
    How can you manage to prevent and control powdery mildew? Air circulation is one of the best ways. Give your plants proper spacing. Any plants that are planted in a heavily shaded area with no air circulation will probably end up with higher humidity. This will help cause the mildew.
     The next best preventative you can do is remove old debris from the garden. This will remove any infected leaves. The less spores the less disease inoculum available to spread through the garden.
     Having an understanding of a few common plants, which can acquire powdery mildew, is helpful. Here is a brief list of plants, then their common name and some resistant cultivars:
    —Monarda spp., Beebalm, ‘Marshall’s Delight’/‘Raspberry Wine’
    —Delphinium spp., Larkspur, ‘King Arthur’/‘Blue Lace’
    —Hydrangea macrophylla, Hydrangea
    —Pelergonium spp., Geranium, ‘Alan Bloom’/‘Biokovo’
    —Phlox paniculata, Phlox, ‘Alpha’/ ‘Pastel Dream’
    —Rudbeckia spp., Black-Eyed Susan ‘Tiger Eye Gold’
    —Rose spp., Rose
    —Salvia spp., Sage, ‘May Night’/‘Rose Queen’
    —Sedum ‘Matrona’, Sedum, Most others are resistant
    —Veronica spp., Speedwell, ‘Icicle’/’Crater Lake’
    —Verbena spp., Verbena, ‘Verbena Aztec Violet’
    ­—Zinnia spp., Zinnia, ‘Oklahoma’/ ‘Profusion’
    Keep an eye on your plants about mid-summer and watch for the first signs of infection. These are leaf curling and spotting. Next comes the white patches on the leaves. As the disease progresses, the buds fail to open and the stems become distorted.

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