The damage due to infection by the fungi causing powdery mildew can be slight to severe. The disease generally occurs during spring, fall and winter months during cool weather with high relative humidity and in shady areas. A powdery, fluffy white to light gray-colored fungus growth on succulent stems, leaves, buds and flowers is the characteristic symptom of powdery mildew. Young plants and actively growing shoots are more severely damaged than older plants, leaves or branches. Infected leaves may be dwarfed, curled or deformed.
Powdery mildew can destroy the blossoms on crape myrtle.
Small dead flecks in the leaves and defoliation may occur on some varieties of azalea and rhododendron that are infected with powdery mildew without the obvious development of white fungus growth. Some highly susceptible plants, such as Chinese photinia or euonymus should be replaced with a similar plant that is not susceptible to powdery mildew. On many trees, the disease causes little or no damage, therefore, control is not necessary. Plants in the landscape which may require fungicide applications to prevent powdery mildew damage include crape myrtle, phlox, rose and zinnia. Sulfur as a spray or dust as needed.