Cures for Mold on Dahlia Leaves

Powdery Mildew

• There are a variety of fungal pathogens that cause powdery mildew to appear on dahlias. Fungal diseases like powdery mildew are not always fatal to plants, but they can be if left untreated. Powdery mildew begins as small white spots of mold on the leaves of the dahlia; as the disease progresses, the leaves will be covered with a white fuzz and gradually curl up, turn yellow and die prematurely. Untreated mold problems spread throughout the garden.

Early Detection

• Catching powdery mildew before it progresses too far is crucial for successfully treating the disease. Avoid overhead watering when watering dahlias, as excess moisture on the leaves provides a place for mold to grow. Check leaves regularly for the presence of fungal spore spots. If these are noticed, it is possible to treat the dahlia with a fungicide that controls the spread of the disease. Fungicides containing propiconazole help stop powdery mildew from spreading; the Clemson Cooperative Extension recommends rotating chemicals and spraying regularly.

Controlling Powdery Mildew

• If powdery mildew has spread to cover the leaves of a dahlia, the plant can still be saved from an early demise. Pinch off all of the infected leaves and remove them from the garden to stop fungal spores from spreading. Pick up any fallen leaves or flowers from around the dahlia plant. Fallen organic matter often acts as a host for remaining spores. Prune any portions of the dahlia that show signs of dieback to prevent them from hosting the disease over the winter.

Preventative Care

• Preventing powdery mildew from returning to attack dahlias in subsequent growing seasons is important for the health of the flowers. Each spring, start a regimen of regular fungicide sprays. As with early detection and control of powdery mildew, rotate the chemicals used to prevent resistant strains of powdery mildew from taking root in the dahlia plant. Keep the growing area of the dahlia clean and avoid over-watering and over-fertilizing the plant, as excess moisture and nitrogen feed fungal pathogens.