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Common Diseases That Pose Problems for Crepe Myrtle Trees

Crepe Myrtle Diseases
With its beautiful blossoms and showy bark, the crepe myrtle is one of the most beautiful landscape trees. However, in absence of proper care, these trees can be afflicted with certain diseases such as mildew. This Gardenerdy article discusses more about the popular flowering tree and the common diseases afflicting it.
Gardenerdy Staff
Last Updated: Dec 10, 2017
Crepe myrtle (Lagerstroemia) is one of the best flowering trees in the world. With approximately 50 species, this tree is cultivated in warmer climates, and is indigenous to Southeast Asia, the Indian subcontinent, and northern parts of Australia. The brilliant fall color of these trees along with the attractive bark and pretty flowers make it the perfect tree for your garden.
You can grow these deciduous trees for ground cover, as a shrub, or like a tree. It has long-lasting flowers, that have a ruffled, crepe-like texture, and are available in colors that range from white, red, lavender, and pink. Crepe myrtle trees bloom in early summer to fall. The exceptionally showy bark sheds throughout the year, and has a beautiful mottled appearance. In fall, the leaf color changes from green to yellow, orange, and red.
Growing Crepe Myrtles
Crepe myrtles are known as the 'lilac of the south'. These trees are very easy to grow in zone 5 and above. You need to choose a location that has well-drained soil and receives full sunlight. Growing the tree in a shady location can lead to many problems like mildew. The planting hole that you dig in the soil should be of the same depth as the container or nursery holding the sapling. Very gently remove the sapling from the container and place it in the planting hole. The roots should be spread out in the hole. Then fill back the planting hole with soil and add water.
You can even add 2 cups of organic fertilizer to the base of the tree, slightly above the root zone. Cover the base with a layer of mulch that is around 3 inch thick. This will help in retaining the moisture in the soil.
When pruning crepe myrtles in winter, it is advisable not to chop off large trees down to ugly stubs. This leads to the growth of thin, whip-like branches that are so weak that they cannot hold the flowers. To reduce the height, you can prune around two to three feet of the topmost branches. Remove the spent flowers once or twice during growing season.
Common Problems
If you are growing crepe myrtle for the first time, then you might make the mistake of planting it deep into the soil. This leads to the lack of oxygen for the root ball. You should make sure the root ball is almost level with the soil. This will help it get oxygen from the atmosphere and allow it to grow well. Some of the problems arise when the pruning is carried out heavily. A tree that is heavily pruned provides all the energy and nutrients to the new leaves and branches. This leads to slow growth and lesser flowers.
Apart from lack of oxygen, this tree cannot survive a long, dry period. You need to provide it with enough moisture during dry season or drought. Therefore, it is important that you mulch around the tree to retain the moisture in the soil.
Common Diseases and Pests
Before you decide to plant a crepe myrtle, it is important to know about the common diseases that afflict the tree.
Aphids
The common garden pests that infect crepe myrtle are aphids. They affect flowering plants and fruiting trees. Aphids are small soft, oval-bodied insects that are a dull yellow in color. They suck out plant sap from tender leaves. After consuming the sugar-rich sap, they excrete a yellow liquid called honeydew. The leaves that are attacked by these tiny pests develop yellow spots mostly on the undersides. These leaves tend to dry out and wilt. Sometimes, certain aphid species cause galls (swelling of plant tissues) on crepe myrtle that is round or spindle-shaped. These galls are full of aphids in different stages of their life. When the crepe myrtle tree has a heavy infestation of aphids, it causes a lot honeydew to accumulate on the tree. This attracts other pests, insects, ants, wasps, mold fungi, and flies. Thus, it is very important that you take immediate steps for controlling aphids.

» Insecticide sprays like Cyfluthrin and Bifenthrin can be used to control aphid populations.

» Alternately, insecticidal soaps can be used for removing the aphids. The best part about this is that these soaps kill the pests while retaining the beneficial insects.

» You can use lady bugs and lacewings to control these aphids. These insects eat up the aphids and help control their growth.
Sooty Mold
Sooty mold indicates the presence of insect infestation. This is a charcoal black fungus that covers the surface of leaves, fruits, twigs, and branches of the trees. This fungus does not cause any pathogenic problems on the tree. It gets its nourishment by feeding on the insect honeydew. When the sooty mold grows thick, it covers the entire leaf. Thus, the tree is unable to carry out photosynthesis. Pests such as whiteflies, scale insects, and aphids produce honeydew. You need to use insecticides to get rid of insects as well as the mold.
Cercospora Leaf Spot
Yellow and orange spots on the upper side and whitish gray spots on the underside of the leaves indicate cercospora leaf spots. The yellow spots appear due to the toxins produced by the fungus and the gray white spots underneath the leaf are the fungal spores. This infection is caused by a fungus cercospora beticola. This is a fungal infection that occurs in moist weather. It can cause complete defoliation of the tree and affect growth of younger trees. You need to plant the trees in sunny areas with good air circulation. You can use a fungicide to get rid of infestation.
Powdery Mildew
One of the most common diseases that affects crepe myrtle is powdery mildew. It causes white or grayish powdery coat on the leaves. Initially, the infection begins as sporadic, circular, and powdery white spots. As the infection spreads, these tiny spots become larger. Soon, the powdery mildew spreads over the entire leaf. This fungal infection inhibits the growth of new leaves and flowers. It may also lead to stunted tree growth. If you find few twigs, leaves, or branches affected by powdery mildew, prune them immediately. Heavily infested trees need fungicide for treatment. You can also try looking for mildew-resistant varieties when choosing the tree.
Japanese Beetle
The Japanese beetles are inch-long pests that love to feed on the foliage and flowers of the crepe myrtle tree. You need to get rid of both the larvae as well as the beetles, to save your tree. You can use insecticides and insect traps for controlling Japanese beetles.
If you take good care, then you can avoid these problems. The special care helps them look the best in your garden.