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powdery mildew My peas have Powdery Mildew

With the rainy, humid, and cool weather we’ve been experiencing this May in Tulsa and Oklahoma City, fungus diseases both in turf and ornamentals are out in full force. Powdery Mildew is one disease that is host-specific to shrubs, flowers, trees, and some vegetables in the vegetable garden. Common susceptible plants are azalea, crabapple, sprirea, euonymous, crepe myrtle, oak, rose, and certain flowers and vegetables. I have a good case of Powdery Mildew in my pea patch at home, but since we’ve just harvested them, it’s no big deal. And yes, they were very yummy!

Powdery Mildew often shows signs of a white, powdery substance forming over the surface of leaves. The powdery fungal growth can usually be found on the upper surface of the leaves, and tends to begin on lower leaves. As the disease progresses, leaves can become dwarfed, curled and somewhat distorted. In severe cases, leaves can turn yellow and even dried and brown. As powdery mildew fungi grow over the plant surface, they develop structures that are inserted into plant cells and extract nutrients necessary for growth and spore production. This results in a general decline in plant growth and vigor of the host, as well as the common visible symptoms.

Powdery Milder thrives in moderate temperatures and high humidities, which is exactly what we have now. As the summer heat comes on and things dry out some, the disease pressure tends to go away. In the meantime, consider pruning to allow better air circulation and more sun exposure to dry things out. Application of a horticulture oil may help if you don’t want to use fungicides. Control can be provided with timely applications of fungicides such as propiconazole (Banner), myclobutanil (Eagle), and thiophante-methyl (Danonil). I’d recommend Eagle for best results. Spraying at the first onset of symptoms is always best, and always follow label instructions.

Fescue turf can at times develop Powdery Mildew, but not to the point of justifying a fungicide treatment. Do bag the clippings to remove the spores, and don’t over-water. As the weather becomes hotter, as it will, the disease pressure will subside.

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