Bee Balm

Set bee balm in full sun and space plants 2 to 2 and a half feet apart. Skip the partly shaded, crowded corner even though it will survive there. Powdery mildew intensifies on overcrowded plants and on plants in partial to heavy shade, so spacing and sun are the cheapest disease control you will ever apply - they dry the leaf surface the fungus needs.

As soon as new growth shows in spring, dig the clump and cut it into sections with a sharp knife, keeping several shoots and a good root system on each. Replant the divisions immediately. Bee balm travels on underground rhizomes and the center of an old clump dies out while the edges crowd themselves - dividing rejuvenates the plant, checks its spread, and reopens the airflow that keeps mildew down.

Keep the soil lightly moist through summer, but deliver water to the ground at the crown rather than sprinkling the foliage. Avoid overwatering, which raises humidity in the canopy. Bee balm wants moisture at the root but wet foliage and humid air are what let powdery mildew and rust take hold, so the delivery method matters as much as the amount.

Through warm humid weather, check leaves low and inside the clump where air moves least, turning them to look at both the upper and lower surfaces. You are looking for a grayish white powdery film, and for leaves dropping early. Powdery mildew produces its spores on both upper and lower leaf surfaces and infected leaves die and drop early. Once mildew growth is extensive, control with any fungicide becomes much more difficult - catching the first colonies is the point at which a spray decision is still worth making.

On a mildew-prone planting, apply wettable sulfur as a protectant before the disease shows, repeating on the label interval while warm humid weather lasts. Once the powder is widespread, stop spraying and plan on a resistant cultivar instead. Sulfur is a protectant that coats the leaf before the spores germinate - UC IPM notes it is effective only when applied before the disease appears, and that once mildew growth is extensive, control with any fungicide becomes more difficult.

Take leafy stems early in the morning, after the dew dries but before the heat of the day, once flower buds have appeared but before they open. Up to 75 percent of the current season's growth can be taken at one time. Hang small bundles upside down in a warm, dry, airy place out of sun until the leaves are brittle. Oil concentration and flavor peak after the flower buds appear but before they open, and once flowering runs on, leaf production declines - the morning cut catches the oils before the sun volatilizes them.

Rake up and destroy the fallen mildewed foliage and any infected debris rather than composting it cold. Cut the dead stems back to 12 to 24 inches and leave those stubs standing through winter. Iowa State advises removing and destroying disease-infested debris in fall, because the litter carries the spores that start next season's epidemic. NC State adds the reason the stubs stay: native bees nest in the dead hollow stems, so cut back to 12 to 24 inches and let them stand until they disintegrate on their own.