|What are the greyish spots on my bee balm and how can we get rid of it?|
|Bee balms may occasionally suffer some minor insect damage. However, powdery mildew is a more serious problem. Powdery mildew is a fungal disease. It appears as a grayish white "powder" on the upper leaf surfaces. Severely infected leaves drop prematurely. Disease symptoms are most severe on overcrowded plants, those growing in partial to heavy shade, and drought stressed plants.
Cultural practices can reduce the severity of powdery mildew. When planting bee balms, select a site in full sun and space plants 1 1/2 to 2 feet apart. Divide plants every 2 to 3 years and water during dry periods. Remove and destroy disease-infested plant debris in the fall. The fungal spores of powdery mildew survive the winter on disease-infested plant debris. The removal and destruction of this material removes the source of next year's infection.
The best way for home gardeners to avoid the annoying problem of powdery mildew is to select mildew resistant varieties. Varieties that possess good mildew resistance include 'Marshall's Delight' (bright pink flowers), 'Gardenview Scarlet' (scarlet-red flowers), 'Violet Queen' (violet-blue flowers), 'Raspberry Wine'(wine-red flowers), and 'Colrain Red' (purplish red flowers).