If grayish-white powder has 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 a popular Southern landscape plant.
Leaves infected early in the season by the powdery mildew fungus become curled and distorted as they expand. Infected younger leaves have blister-like areas which quickly become covered with the mildew. On older leaves, large white patches of fungus growth appear, but there is little leaf distortion. Flowers which originate from infected buds often become blighted.
Powdery mildew has been more common this season because of dry weather, warm days and cool nights -- conditions which favor development of this disease. If powdery mildew is showing up in your crape myrtle landscape planting what should be done about it? 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.
Homeowners who have had severe crape myrtle powdery mildew problems in past seasons should start fungicide application immediately after the first sign of the disease. It may be necessary to continue fungicide sprays until leaves are mature, at which time they are less susceptible to the powdery mildew fungus. Also, fungicide applications can be made during the flowering period to prevent blossom blight infection.
By the way, Powdery Mildew (also called White Powdery Mildew by myself and many others) not only happens on Crapes, but can affect Roses, Annuals, Perennials, Vegetables etc.
Fungicides to Wash It Off –
Consan Triple Action 20
Banner-based Fungicides (Fertilome Liquid Systemic/Ortho Banner-based)
Home Made Baking Soda Spray (2 teaspoons of B.S.; 2 Quarts of water; ˝ teaspoon of dish soap or even Murphy’s Oil Soap)
Fungicides to Prevent It –
Banner-based Fungicides (see above)
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