Hello Gardeners, I’m Amanda McNulty with Clemson Extension and Making It Grow. Powdery mildew is a fungal disease that affects many of our garden plants and was so damaging to older varieties of phlox paniculata, tall garden phlox, that we couldn’t grow that plant in many parts of the south until resistant varieties came on the market. Resistance doesn’t mean immunity so we shouldn’t crowd plants but provide good air circulation. Powdery mildew affects grasses, trees, flowers, weeds, shrubs and vegetables – but each one is specific to the plant it harms. The fungus that grows on phlox can’t grow on cucumbers or on crape myrtles. Interesting, powdery mildew is worse in hot –dry – conditions – it requires high relative humidity but not a wet leaf. Most other fungal pathogens need twelve hours of wet leaf surface to penetrate and cause disease which is why we avoid watering foliage late in the day when it won’t dry before nightfall.
Powdery Mildew and Phlox
