Flowers may be white, pink, red or purple. While beebalms can be beautiful plants, powdery mildew often makes them unsightly. Severely infected leaves drop prematurely. Disease symptoms are most severe on overcrowded plants and those growing in partial to heavy shade.
Cultural practices can reduce the severity of powdery mildew.
When planting beebalms, select a site in full sun. Remove and destroy disease-infested plant debris in the fall. The fungal spores of powdery mildew survive the winter on disease-infested plant debris. Removing and destroying this material eliminates the source of next year's infection. Fungicides also can be used to control powdery mildew.