My Crape Myrtle Tree Has Black on the Branches in Fall

Features

• Crape myrtles grow as shrubs or trees up to 20 feet high. Blooming with summer flower clusters, they are sun-loving plants. Aphids, scale insects, whiteflies and other bugs feed on the myrtle, sucking out sap and excreting honeydew. The sweet and sticky excretions drip onto leaves and branches. Common molds develop in the honeydew, coating the plant with black and sooty, unsightly mold deposits. These molds develop over the summer due to the insect infestations and become more visible in autumn as the flowers and leaves fall from the tree.

Insects

• Inspect the tree for insects. Usually you will see aphids on the underside of leaves, above the black branches. Their excretions drop down onto branches below. Because the insects are the problem, they must be removed or reduced in numbers to stop the spread of the sooty mold fungi. Most insects can be blasted off the tree with a jet of water. Insecticidal soap is effective, but usually must be reapplied when insects return. Other insect controls include spraying with pyrethrins, malathion, horticultural oil, systemic insecticide or applying a soil drench. Look for products that kill sucking insects on flowering trees or shrubs.

Sooty Mold

• Heavy deposits of sooty mold can accumulate on the myrtle, making leaves and branches look dirty and black. The molds are more common in mild summer and autumn temperatures. Although they are unsightly, the molds live off the insect excretions and do not feed off the tree. Sooty molds usually do not affect the tree, but when heavy growths are on the leaves and branches for prolonged periods, they block needed sunlight and cause crape myrtle health problems. After the insects are removed or under control, blast the sooty mold off the tree or use mild dish soap, 4 ounces per gallon of water, to spray and loosen the mold. Wait a few minutes and spray again with water to loose and strip off the mold.

Tips

• Unless the plant has heavy infestations, beneficial predators like ladybugs reduce the insect population, and you don't need to spray aphids and other pests. If your tree is taller and you cannot see the culprits, look for steady streams of ants on the tree. They are attracted to honeydew and are good indicators of aphid infestations. When the sticky honeydew drips off the tree and lands on chairs or other garden furniture, sooty mold soon coats the items. Wash with mild soap and water.