|EVERY YEAR IN LATE SUMMER MY CRAPE MYRTLES TURN BLACK. THEY LOOK AS IF THEY HAVE BEEN BURNED. WHAT IS THIS AND HOW CAN I PREVENT THIS?|
|There are two possible causes for leaves turning black. One is sooty mold caused by insect feeding and the other is a fungal disease. When aphids feed they excrete a sticky substance called honeydew. This substance turns black as it ages. It can be washed off or scraped off the leaves with a fingernail. If the black is a coating on the leaf surfaces, it's sooty mold and you will need to spray the insects to control the problem. Insecticidal soap applications can help.
A tip blight caused by a fungus sometimes attacks crape myrtles. Leaves near the branch tips turn brown in late spring or early summer. Tiny black spore-bearing bodies appear on infected leaves. Spray plants with copper fungicide or lime sulfur fungicide when symptoms first appear and then every 10 days in wet seasons. Avoid overhead watering which keeps foliage moist and fosters the disease. Prune to increase air circulation around plants, taking care to sterilize pruning tools by dipping them in household bleach to avoid spreading the disease. Because the fungus spores collect on the mulch beneath the shrubs, removing the old mulch and replacing it with fresh material may help prevent an outbreak from recurring.
If this blight is a common problem every year, prune and destroy affected plant parts in the early spring. Spray a copper fungicide or lime sulfur in four applications: (1) after the dead leaves and dying branches have been removed and before growth starts in the spring; (2) when growth is half completed; (3) after spring growth has been completed; and (4) after fall growth stops. Take care to determine if the crape myrtle twigs are turning brown from frost damage rather than disease.