Powdery Mildew Diseases of Ornamental Plants

Powdery mildews are one of the most common diseases of ornamental plants; many nursery, flower, and woody plants are susceptible. Greenhouse crops prone to infection include African violet, Begonia , Dahlia , gerbera daisy, Hydrangea , roses, Verbena, Kalanchoe, and poinsettia. Herbaceous perennials particularly susceptible to Powdery mildew include Aster, Centaurea, Coreopsis, Delphinium, Monarda, Phlox, Rudebeckia, and Sedum.
The disease is easily recognizable as a white to gray powdery growth on leaves and sometimes stems and flowers. Powdery mildew may have little or no affect on the plant (other than aesthetic) or it may cause infected leaves to distort, discolor, wither, and defoliate prematurely. Most Powdery mildews have evolved to avoid killing their hosts because they can only survive in living plant tissue. Symptoms and their severity depend upon the cultivar or species of host plant, the powdery mildew species, environmental conditions, and the age of plant tissue when it first became infected. Powdery mildew diseases are caused by species of fungi such as Erisyphe, Leveillula, Microsphaera, Podosphaera, Odium, and Sphaerotheca, although each powdery mildew is specialized to infect only hosts in one genus or one family. Infection does not spread to species of plants in other plant families. Erisyphe has a wide host range and can infect many plants in the Asteraceae family, while Sphaerotheca pannosa var. rosae is confined to roses.

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