Answer: If grayish-white areas recently appeared on the new growth of your crape myrtles, chances are the problem is powdery mildew. In extreme cases, entire twigs may be blighted by the mildew fungus. While this fungus disease will not kill affected crape myrtles, blighted foliage detracts from the appearance of your crape myrtle. If infection isn't excessive, infected twigs may simply be removed by pruning. Heavily powdery mildew infected plants will probably require fungicide treatment for full recovery. Although several fungicides help reduce crape myrtle powdery mildew, the most effective products are Spectracide Immunex or Immunox. Apply Immunex (1 ? fl. oz. per gallon of water) every 21 days or Immunox (2 fl. oz. per gallon of water every 14 days) until disease control is obtained. These fungicides may also be used for the control of powdery mildew, and other diseases, on roses, dogwoods, as well as other ornamental plants.
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