The 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. Fungicides can also be used to control powdery mildew. Probably the best way for home gardeners to avoid the annoying problem of powdery mildew is to select mildew resistant varieties. In 1993, the Chicago Botanic Garden evaluated the mildew resistance of 41 beebalm varieties over a 4 year period.