Eco-friendly Powdery Mildew Control
Don’t panic when you find your zinnias, lilac, bee balm or phlox leaves are covered with a white powdery substance. This fungal disease, known as powdery mildew, is often a yearly problem on a variety of plants.
This particular fungus grows on leaf surfaces, preventing sunlight from reaching the leaves. The infested leaves eventually turn yellow, brown and may wither. The disease won’t kill the plant – it just looks bad.
So what can you do? Start with resistant varieties of susceptible plants like Garden View Scarlet bee balm or David garden phlox. Grow plants in full sun and properly spaced for good air circulation and less risk of disease.
If you decide to treat, try one of the more eco-friendly products. Cornell University found mixing one tablespoon of baking soda with one teaspoon insecticidal soap or lightweight horticulture oil in a gallon of water works well.
Spray the Cornell mix or Neem, a plant derived fungicide, weekly. Start at the first sign of the infection and repeat as needed until the end of the season.
A bit more information: Further reduce the risk of powdery mildew with a bit of spring grooming. Remove one fourth of the stems of garden phlox, bee balm and other susceptible perennials in spring when the plants are several inches tall. This increases light penetration and air flow, resulting in stronger stems and less risk of this disease. Or, live with the damage and plant slightly shorter plants in front of the mildew susceptible flowers. The neighboring plants will block the view of the unsightly foliage, but still allow the flowers on the mildew susceptible plants to brighten the garden.