White Fluffy Fungus
One of the challenges with gardening is to keep an eye out for unwanted growths appearing on plants. Several fungal pathogens can cause white, fluffy growths on leaves, stems, flowers or the surrounding soil. Some fungal diseases only cause cosmetic issues, while others can cause serious damage to infected plants if left untreated.
Various fungi cause downy mildew while other fungal pathogens cause powdery mildew, both diseases that cause white, fluffy growth to appear on the foliage of fruits, vegetables and ornamental plants. With downy mildew, the cottony growth appears on the undersides of leaves, while small, light yellow spots appear on top of the foliage. These spots might enlarge and merge to form large lesions. Infected leaves often drop prematurely from the plant. Severe infections can kill a plant.
Powdery mildew disease causes a powdery, white to grayish-white growth to appear on the tops of leaves, but occasionally the fluff forms on the undersides of leaves as well as on the stems, flowers or fruits. Infected leaves can curl up, look distorted and new growth may be stunted. Powdery mildew infections might make your plant look unattractive, but this disease rarely kills.
White mold is caused by fungal pathogens (Saprophytic spp.) that attack more than 370 different plants, including vegetables, perennials and annuals. Early signs of white mold include wilted foliage and a white, fluffy growth that appears on leaves or blooms only during wet weather. After about a week, the white fluff turns into a darker sclerotia, a structure that protects the fungal pathogens. Other signs of a white mold problem include brown, water-soaked spots forming on stems. These spots often grow and turn into soft, slimy, rotting plant tissue. The leaves above infected stems turn yellow or brown before falling from the plant. White mold infections can kill entire plants.
Fungal disease pathogens germinate and spread quickly when humidity levels run high. Lower the humidity levels around your plants by increasing the space between them to increase air flow. Prune out crowded interiors to allow ample circulation throughout entire plants. Avoid using overhead watering systems and water your plants early enough in the day that the foliage can thoroughly dry in the sun. Help prevent powdery mildew by planting susceptible varieties in sunny parts of the garden. Remove any diseased plants to prevent fungal infections from spreading. Avoid attracting white mold pathogens by planting only in well-draining soil.
No chemical controls exist for white mold once it occurs, and fungicidal treatments aren't recommended for downy mildew problems in home gardens. You can use a simple, homemade recipe to treat mild to moderate powdery mildew infections. Combine 2 1/2 tablespoons of lightweight horticultural oil and 4 teaspoons of baking soda in 1 gallon of water. Thoroughly spray the foliage with the solution and repeat treatments every seven to 10 days during humid weather to help prevent new infections.
- The University of Georgia College of Agricultural & Environmental Sciences: Downy Mildew
- Oklahoma State University Entomology & Plant Pathology: Downy Mildew of Ornamentals
- University of California UCNFA News: Management of Downy and Powdery Mildews: Three New Diseases Hit California
- North Carolina State University: Powdery Mildew of Ornamentals and Shade Trees
- University of Illinois Extension: Sclerotinia White Mold
- Oregon State University Extension Service: Controlling Powdery Mildew With Horticultural Mineral Oil
- University of California Statewide Integrated Pest Management Program: Powdery Mildew on Ornamentals