Producing large clusters of brightly colored blooms, hydrangeas (Hydrangeas) provide a cottagelike feel to gardens in U.S. Department of Agriculture hardiness zones 3 through 9. When the hydrangeas show symptoms of a fungal disease, immediate action will help reduce the damage and increase the plants' survival rate. Unfortunately, commercial fungicides add unnecessary chemicals to the environment and may not control the fungus. Instead, opt for organic ways to treat fungal problems.
A highly contiguous fungal disease, powdery mildew affects many different species of plants, including hydrangeas. It presents itself with a white, powdery growth appearing on branches and leaves. The leaves begin to yellow, brown, wilt and fall from the plant. The hydrangea's shoots and leaves may distort and twist. Powdery mildew thrives in shaded areas and temperatures of 60 to 80 degrees Fahrenheit but does not require moisture to grow. A homemade solution of 2 to 3 drops of dish soap that does not contain heavy fragrances or bleach, 1/2 tablespoon of baking soda and 1/2 gallon of water will change the pH balance and prevent powdery mildew from spreading and forming. Liberally mist the foliage with the solution for an organic control of the fungus.
Sooty mold produces a fuzzy, black substance that covers buds, stems and leaves and can interfere with the hydrangea's photosynthesis ability. Sooty mold forms on honeydew, which is a sticky substance secreted by garden pests such as aphids. Once these pests are gone, the sooty mold will wear off on its own, or you can gently wipe off mold with a damp towel. Introducing predatory insects will control honeydew-secreting pests. These beneficial insects -- predatory wasps, lacewings and ladybugs -- are available for purchase at garden centers. Alternatively, plant flowers -- such as marigold, tansy and fennel -- to attract the predatory insects to your garden.
The same chamomile tea that you drink will help hydrangeas inflected with mildew and fungus. Simmer 16 chamomile tea bags in 2 quarts of water for about 20 minutes.Then remove the tea from the heat and let it steep for at least four hours. Chamomile tea contains anti-fungal and anti-bacterial properties that combat fungus and mildew. Transfer the tea to a spray bottle and liberally mist the leaves of the hydrangeas.
Creating a foliar spray of two aspirin tablets dissolved completely in 1 quart of water and applying it to the hydrangea will treat damaging fungal diseases such as powdery mildew, black spot and rust. Just be sure to use aspirin tablets that are uncoated.
If the hydrangea is under attack from viral, bacterial or fungal diseases, create a homemade garlic spray to combat the disease. Chop up two garlic cloves in a blender for a few minutes. Add about a quart of water to the blender, blend for six minutes and carefully strain the mixture into an airtight container. Mix in 1/8 teaspoon of dish soap and cover the container until ready to use. Before applying the garlic mixture, dilute it with water at a ratio of 1 part garlic mixture to 10 parts water and transfer it to a spray bottle. Thoroughly coat the leaves -- tops and underside -- with the mixture to get rid of the disease.
Keeping the hydrangea healthy and actively implementing good cultural control reduce the possibility of fungal problems. Water the hydrangea early in the morning to allow the plant enough time to dry before the sun sets. In addition, forgo watering the hydrangea from above and instead apply the water at the base of the shrub. When you notice living, dead or decaying plant matter has fallen on the garden, remove and dispose of it immediately.
- University of California Integrated Management Program: Hydrangea—Hydrangea spp. Family Saxifragaceae (Saxifrage Family)
- Fine Gardening: Genus Hydrangea
- Lady Bird Johnson Wildflower Center: Powdery Mildew Hits Rock Rose in Round Rock Texas
- UC IPM Online: Sooty Mold
- Fine Gardening: 35 Pest and Disease Remedies
- Jupiterimages/Creatas/Getty Images