One scourge of the flowering perennial bee balm (Monarda didyma) is powdery mildew. This fungal disease can take a beautiful stand of bee balm and turn the leaves into a dry, white crusty powder by midsummer. In my garden, I've always noticed that different varieties show different susceptibility to powdery mildew, and now research from the University of Vermont and Chicago Botanic Garden confirm that one variety is significantly less likely to get the disease.
In a three-year study comparing 17 different varieties of bee balm, Leonard Perry, ornamental plant specialist at the University of Vermont, concluded that the most disease-resistant bee balm was 'Marshall's Delight'. On average during the trial period, fewer than 20 percent of the leaves showed mildew.
Likewise, Richard Hawke, horticulturist at the Chicago Botanic Garden, concluded that, of the 38 varieties he tested over four years, 'Marshall's Delight' showed best growth and disease-resistance. In the trial period, no more than 5 percent of its foliage became infected. If mildew is a problem in your garden, consider growing this 3-foot-tall beauty with bright pink flowers.
Charlie Nardozzi is senior horticulturist at National Gardening.