Pest Control Library: Powdery Mildew

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By National Gardening Association Editors

This fungus disease occurs all over the North America and infects a wide variety of plants, including beanscucurbitslettuce, and peas. A powdery white growth covers the upper surface of leaves, which eventually turn yellow and dry. Older leaves are usually infected first. The fungus competes with the plant for nutrients, reducing yields and weakening or even possibly killing it if infection is severe. Fruits and pods may also be covered with mildew. This disease usually develops late in the season on mature plants and thrives in both dry and humid weather. It can spread rapidly.

  • Photo by Suzanne DeJohn
  • Prevention

    Preventing powdery mildew is crucial for maintaining healthy vegetables and reducing the need for treatments later. Here are some preventive measures:

    • Select Resistant Varieties: Choose vegetable varieties that are resistant or less susceptible to powdery mildew. Seed catalogs and plant tags often indicate resistance.

    • Proper Spacing and Air Circulation: Plant vegetables far enough apart to allow for good air circulation. This reduces humidity around the plants, which is conducive to powdery mildew development.

    • Adequate Sunlight: Ensure your vegetable garden receives ample sunlight, as powdery mildew thrives in shaded areas.

    • Watering Practices: Water plants at the base to avoid wetting the foliage. Wet leaves can promote fungal diseases. Morning watering is preferable to give plants time to dry during the day.

    • Regular Monitoring: Keep an eye on your plants for early signs of infection so you can take action immediately.

    Organic Controls

    If prevention measures fall short and you notice signs of powdery mildew, here are some organic treatment options:

    • Remove Affected Parts: Prune and dispose of infected leaves or plant parts to reduce the spread of the fungus.

    • Neem Oil: Apply neem oil to affected plants. Neem oil is a natural fungicide and insecticide that can help control powdery mildew without harming beneficial insects.

    • Baking Soda Spray: Mix 1 tablespoon of baking soda, 1/2 teaspoon of liquid soap, and 1 gallon of water. Spray the mixture on affected plants. The baking soda alters the surface pH, making it less hospitable to powdery mildew.

    • Milk Spray: A solution of milk and water (1 part milk to 2-3 parts water) has been shown to be effective against powdery mildew on some vegetables. The exact mechanism is not fully understood, but it's believed that the proteins in milk act as an antiseptic.

    • Sulfur and Copper-Based Fungicides: These are traditional organic fungicides effective against a broad range of fungal diseases, including powdery mildew. Use according to the label's directions, as they can be harmful to beneficial insects and plants if misused.

    Conventional Controls

    If organic controls do not effectively manage the powdery mildew problem, you may consider conventional fungicides as a last resort. Here are some options:

    • Systemic Fungicides: These fungicides are absorbed by the plant and can provide protection and treatment from within. They are effective but should be used sparingly and as directed to avoid resistance.

    • Contact Fungicides: These products are applied directly to the plant surface and act on the powdery mildew spores and mycelium present on the leaves. Repeated applications may be necessary.

    Always follow the label instructions carefully when using any fungicides, whether organic or conventional. Rotate between different fungicides to prevent resistance development in the powdery mildew population.

    Together with Victory Seed Company:
    Victory Seed Company Logo Victory Seed Company has all the seeds you want for your best garden in 2024.

    For 25 years, the family-owned Victory Seed Company has provided the highest quality vegetable, herb and flower seeds to families across the country. We are passionate about providing you the best seeds available that give excellent germination, robust plants, and the harvest you want. With a catalog of over a thousand varieties, we have everything, and our prices are the kinds that we'd want to pay. We have hundreds of yesterday's heirloom vegetables, as well as today's award winning hybrid selections. Get to know us by visiting our website and browsing through our online vegetable seed catalog.

    This article is a part of our Pest Control Library.
    This article is a part of our Pest Control Library.
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