Powdery Mildew

• Powdery mildew is the cause of white spots and coating on the leaves, twigs and stems of crape myrtle. It is a fungal infection that is spread by contact between plants and also by the wind between neighboring plants. It resembles a powder coating that appears as though it could be washed away by spraying or a hard rain. Small infections cover a few leaves or a small area, while severe infections will cover most of the tree including the branches and flowers.
  
  

Symptoms

• In addition to the white coating, crape myrtle suffering from powdery mildew will begin to lose foliage. Over time the leaves turn yellow or brown and drop from the plant. Emerging leaves will not grow to full size and may emerge curled or with a wilted appearance. Some affected leaves will have a rust coloring underneath the white coating. In severe cases, the plant will fail to bloom.
  
  

Treatment

• Once a crape myrtle is infected, the best treatment is removal of infected areas and application of a fungicide. If only a small area is covered in powdery mildew, prune away the leaves and stems showing symptoms. Spray a fungicide on the entire plant to stop the spread of the fungus. Choose a fungicide that contains lime sulfur, thiophanate-methyl, triadimefon or propiconazole. Re-apply the fungicide every seven to ten days while conditions remain ideal for powdery mildew, such as during the hot, dry days of summer.
  
  

Prevention

• Planting varieties of crape myrtle resistant to powdery mildew is the best prevention, but for existing trees other practices can reduce the incidence of the fungus. Do not allow sprinklers or overhead water to fall on the plant, but water the roots only. Make sure the plant receives full sun, at least six to eight hours a day. Remove any suckers from the crape myrtle as soon as they appear, and avoid fertilizing during the summer. Pruning to improve air circulation within the plant is also helpful.