WATCH: What's Wrong With My Crepe Myrtle? 4 Common Problems
Crepe myrtles come in all different colors and heights, so find the one that's right for you. For vibrant summer color, few flowering plants can compete with the crepe myrtle. Just look around your neighborhood. Nearly every street in the South is lined with these blooming trees from mid-June to mid- August. There's plenty to love about them: They grow almost anywhere, are easy to maintain, and are available in all shapes, sizes, and shades. When picking one for your yard, ask yourself: What color flowers do I want? Choose from red, white, purple, or pink. Is it cold hardy enough? This is key if you live in the Upper South. Is there plenty of sunlight? The more sun, the more flowers you'll get. How big will it grow? Crepe myrtles have a reputation for growing fast. A larger one can overwhelm your landscape, which could result in the ill-advised pruning practice known as "crepe murder." At right are four of our favorite selections.
Problem #1 -- Sooty Mold
Problem: Sooty Mold
Sooty mold is a fungus that covers the leaves and looks like you just sprayed your crepe myrtle with asphalt. (Note to reader: This is seldom a good idea.) The mold doesn’t feed on the foliage. Instead, it grows on sticky honeydew secreted by sucking insects like aphids, scales, and white flies that do feed on the leaves. Get rid of the bugs and black mold will go with them.
A black spotlike mold covers the leaves. Rubbing removes the mold. Underneath, the leaves are green and healthy.
Sooty molds are also called black molds. These unsightly molds are caused by several species of fungi. More than one sooty mold fungus may appear on the same plant at the same time, feeding on the honeydew of numerous insects. Fungal growth takes place from spring through early fall. Splashing rain or water may spread the fungus to other plants.
Symptoms: Sooty mold usually appears as a dark, brown-black powdery fungus growth covering leaf surfaces and twigs. It can also look like a thin, dark film or black spots. In several cases, the fungus almost completely covers a leaf’s surface. Although the fungus is considered fairly harmless because it does not feed on plants, extremely heavy infestations can block sunlight from reaching the leaves, which may yellow and fall prematurely.
Solution: Look for aphids, scales or leafhoppers higher in the plant. They secrete a sticky substance called honeydew, on which sooty mold grows. Control these insects by blasting them of with water or by spraying with horticultural oil, azadirachtin (Neem), malathion, or acephate (Orthene). Spray your crepe myrtle according to label directions with insecticidal soap, horticultural oil, neem oil, or Natria Multi-Insect Control. All of these are safe, natural products available at home and garden centers. Without the insects and their honeydew, sooty mold will gradually wash away.
Prevention: Control scale, aphids, mealybugs, whiteflies, and other honeydew-excreting insects, as well as ants.
Control: On small plants, wipe or wash off the molds with a small sponge and water. On large trees, use a hose-end sprayer to wash off mold. Spray plants with malathion, horticultural oil, azadirachtin (Neem), or acephate (Orthene) to control insects that secrete honeydew.
STICKY SITUATION: Some sap-sucking insects do not fully digest plant sap. The undigested portion is excreted as a sweet, sticky liquid called honeydew. If copious amounts of honeydew form on trees, sidewalks and other surfaces below may become coated with it and the sooty mold that follows. Ants add to the problem by collecting and tending honeydew-excreting insects, such as aphids, scale, and mealybugs. They milk the insects for the honeydew, which they take back to other ants for food. Ants also transfer honeydew-excreting insects from plant to plant.
Problem #2 -- Powdery Mildew
Problem: Powdery Mildew
The bizarrely cool, rainy summer we’ve experienced in the Southeast this year (sorry, everybody out west) means that if your crepe myrtle is susceptible to mildew, it probably has it. Powdery mildew is a filmy, white fungus that grows on leaves and flower buds. It causes leaves to curl and shrivel. Flower buds drop without opening. Back in the day when we didn’t have resistant selections, powdery mildew was the #1 complaint people had about crepe myrtles.
White powdery spots appear on leaves, stems, and flowers. The spots expand to completely cover leaves in only a few weeks. If the fungus spreads to flower buds, the buds may not open.
There are many different powdery mildew fungi. The fungus spores overwinter on fruit trees. In spring, the fungus begins to grow, and spores are released to travel on the wind to young leaves. Powdery mildew thrives where cool nights follow warm days. Insufficient sunlight and poor air circulation favor its development.
Symptoms: A white or gray powdery fungus appears on foliage and flowers. Round, white spots on upper leaf surfaces expand and merge, covering both sides of leaves. Infected leaves turn yellowish green to brown. New growth may be stunted, curled, and distorted. Infected blossoms may not set fruit; fruit may develop a rough skin or be covered with the powdery fungus. Fruit drops early or is dwarfed.
Solutions: Plant a mildew-resistant crepe myrtle. Almost all of the newer ones are resistant, including those named after tribes of native Americans, such as ‘Acoma,’ ‘Arapaho,’ ‘Catawba,’ ‘Comanche,’ ‘Miami,’ ‘Natchez,’ ‘Sioux,’ ‘Tonto,’ and ‘Zuni.’ ‘Dynamite,’ ‘Early Bird,’ ‘Pink Velour,’ and ‘Red Rocket’ resist it too. If yours isn’t resistant, spray the foliage according to label directions in early summer with neem oil, horticultural oil, Natria Disease Control, Daconil, or Immunox. The first three are natural products. You’ll probably have to spray more than once.
Powdery mildew usually strikes during periods of warm, humid weather. Apply horticultural oil, triadimefon (Bayleton), or triforine (Funginex) at the first sign of the disease. Consider planting a mildew-resistant selection, such as ‘Acoma,’ ‘Biloxi,’ ‘Hopi,’ ‘Lipan,’ ‘Miami,’ ‘Natchez,’ ‘Sioux,’ ‘Yuma,’ and ‘Zuni.’
Prevention: Plant resistant selections; see the “Southern Living Garden Book” under the “Practical Gardening Dictionary” or individual plant listings for suggestions. Give plants sufficient light and air circulation. Water plants from underneath rather than above to keep leaves dry.
Control: Reduce nitrogen fertilizer. Pick off and destroy infected leaves and flowers/ Spray ornamentals with horticultural oil triforine (Funginex), thiophanate-methyl (Thiomyl, Domain), azadirachtin (Neem), or triadimefon (Bayleton). Spray fruits and vegetables with wettable sulfur or horticultural oil. Discard infected flowers of annuals and leftover produce in fall.
Problem #3 -- Cercospora Leaf Spot
Cercospora is a leaf spot fungus that used to be fairly uncommon, but isn’t anymore. Grumpy has a theory that the nearly universal planting of crepe myrtles in the South has made it easy for this fungus to spread. What happens is that in mid- to late summer, angular, brown spots form on the oldest leaves. These leaves then develop fall color prematurely and drop. By fall, the tree may be completely defoliated, except for a few newer leaves at the top. Fortunately, this seems to cause no ill effects the next year.
Solutions: This fungus likes sheltered areas where breezes are blocked and the foliage stays wet for long periods. Grumpy knows this, because the one he planted in front of his house gets eaten up by leaf spot every year, while the one growing in the middle of the lawn is hardly touched. Some websites claim certain selections are resistant, such as ‘Apalachee,’ ‘Catawba,’ ‘Sioux,’ ‘Tonto,’ ‘Tuscarora,’ ‘Tuskegee,’ and ‘Yuma.’ Grumpy has his doubts, because the one that gets devoured every year is ‘Sioux.’ What to do? Plant crepe myrtles in open, sunny spots where air circulates freely. If necessary, spray with Daconil, Immunox, or Natria Disease Control when spots begin to appear.
Problem #4 -- No Blooms
No matter where you live in the South, crepe myrtles should have bloomed by now. If yours hasn’t, most likely it’s due to one of three reasons.
1. Your plant is just too small to bloom. Give it time.
2. Your plant isn’t getting enough sun. It likes full sun.
3. Some crepe myrtles bloom better than others. You may have a slacker. If so, replace it with one of the selections named above.
Attention: No ants were harmed in the production of this post.
Another Problem You Might Not Think About: Asian ambrosia beetles
A tiny, foreign invader now threatens peach, plum, pear, pecan, and many other trees in the South — the Asian ambrosia beetle (Xylosandrus crassiusculus). Less than ¼ inch long and cylindrical in shape, it is dark brown, reddish brown, or black and may have pitted wing covers. It entered this country in 1974 near Charleston, South Carolina. Since then, it has spread into North Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, and Texas.
It’s much easier to detect the beetle’s presence than the insect itself. A telltale clue is a white, toothpicklike spike of boring dust that protrudes about 1 ½ inches from the trunk. Female beetles produce theses spikes as they excavate galleries or corridors inside the tree for laying eggs.
Branches wilt and die back. Sawdust protruding from holes in branches looks like tiny toothpicks stuck to the bark.
Solution: These tiny beetles attack both stressed and healthy plants. They lay eggs inside stems and introduce a fungus (ambrosia) with which to feed their young. The fungus clogs the plant’s water transport system and produces toxins, both of which result in wilting. You can reduce stress on plants by making sure they are watered correctly, fertilized annually, and kept free of disease. Once several beetles have invaded the plant, insecticides are not effective. Prune and destroy infested limbs. For prevention, thoroughly spray trunks of susceptible plants nearby with diazinon, endosulfan (Thiodan), or chlorpyrifos (Dursban).
Damage: These aggressive beetles attack both healthy and stressed trees. Attacks on healthy plants usually occur near ground level or at wound sites. As many as 50 beetles may infest a single tree. Beetles excavate a maze of tunnels and cultivate ambrosia fungus (Fusarium solani) on the tunnel walls to feed their developing young. Infested trees may wilt and die.
Life cycle: While adult beetles are present most of the year, they require high humidity to reproduce. Major activity occurs in March. Females bore into stems, twigs, branches or trunks of young trees. They deposit eggs within tunnels and introduce the fungus. Females remain with their young until they mature and exit the tree. Hatching females mate before leaving the tree to infest a new host.
Prevention: Keep trees vigorous with adequate watering and fertilization. Avoid wounding them. Spray trunks with chlorpyrifos (Dursban) or endosulfan (Thiodan) late in the day, so the chemical can dry overnight and avoid breakdown due to sunlight and heat. You can also spray with diazinon. Follow label directions carefully.
Control: Once beetles are in the tree, no chemical will help. Remove and burn the infested tree.
More on Crepe Myrtles
The crepe myrtles are among the most satisfactory of plants for the South: showy summer flowers, attractive bark, and (in many cases) brilliant fall color make them year-round garden performers. Long, cool autumns yield the best leaf display; sudden frosts following warm, humid fall weather often freeze leaves while they’re still green, ruining the show.
Most crepe myrtles in gardens are selections of L. indica or hybrids of that species with L. fauriei. The latter species has attracted much notice for its hardiness and exceptionally showy bark. Queen’s crepe myrtle, L. speciosa, grows only in the Tropical South.
All crepe myrtles bloom on new wood and should be pruned in winter or early spring. On large shrubs and trees, remove basal suckers, twiggy growth, crossing branches, and branches growing toward the center of the plant. Also gradually remove side branches up to a height of 4-5 feet; this exposes the handsome bark of the trunks. During the growing season, clip off spent flowers to promote a second, lighter bloom. Also prune dwarf forms periodically throughout the growing season, removing spent blossoms and thinning out small, twiggy growth.
Crepe myrtles are not usually browsed by deer.
L. fauriei. JAPANESE CREPE MYRTLE. Native to Japan. Tree to 20-30 feet tall and wide, with erect habit and outward-arching branches. Light green leaves to 4 inches long and 2 inches wide turn yellow in fall. Especially handsome bark: The smooth gray outer bark flakes awawy to reveal glossy cinnamon brow nbark beneath. Small white flowers are borne in 2- to 4-inch long clusters in early summer; often blooms again in late summer. Resistant to mildew and best known as a parent of hardy, mildew-resistant hybrids with L. indica, though it is handsome in its own right. ‘Fantasy,’ with even showier bark than the species, has a vase form — narrow below, spreading above. ‘Kiowa’ has outstanding cinnamon-colored bark.
L. indica. CREPE MYRTLE. The premier summer-flowering tree of the South. Tolerates heat, humidity, drought; does well in most soils as long as they are well drained. May be frozen to the ground in severe winters in the Upper South, but will resprout. Gardeners there should plant cold-hardy selections such as ‘Acoma,’ ‘Centennial Spirit,’ and ‘Hopi.’ Variable in size (some forms are dwarf shrubs, others large shrubs or small trees) and habit (spreading or upright). Dark green leaves are 1-2 ½ inches long and somewhat narrower, usually tinted red when new; they often turn brilliant orange or red in fall. Crinkled, crepe-papery, 1- to 1 ½-inch wide flowers in white or shades of pink, red, or purple are carried in dense clusters.
Trained as a tree, it develops an attractive trunk and branch pattern. Smooth gray or light brown bark peels off to reveal smooth, pinkish inner bark; winter trunk and branches seem polished.
Mildew can be a problem. Spray with triforine (Funginex) before plants bloom, or grow mildew-resistant hybrids of L. indica and L. fauriei. Almost all selections with names of Native American tribes, such as ‘Hopi,’ ‘Miami,’ and ‘Zuni,’ are mildew resistant.
L. speciosa. QUEEN’S CREPE MYRTLE. Tree to 25-30 feet tall, 15-25 feet wide. The showiest and most tender of the crepe myrtles, displaying huge clusters of white, pink, lavender or purple flowers in June and July. Individual blossoms reach 3 inches across. Large leaves (8-12 inches long, 4 inches wide) turn red in fall. Smooth, mottled, exfoliating bark. Rank grower; annual pruning in winter is especially important to control size and form.
DON’T COMMIT “CREPE MURDER”
Don’t chop your large crepe myrtles down to ugly stubs each spring just because your neighbors do. This ruins the natural form and encourages the growth of spindly, whiplike branches that are too weak to hold up the flowers. To reduce a crepe myrtle’s height, use hand pruners or loppers to shorten the topmost branches by 2-3 feet in late winter, always cutting back to a side branch or bud. For branches more than 2 inches thick, always cut back to the crotch or trunk. Don’t leave big, ugly stubs.
WHAT CREPE MYRTLES NEED
PLANTING SITE: A sunny location where the air moves freely will help limit powdery mildew and other diseases.
SOIL: Provide moist, moderately fertile, well-drained soil.
PRUNING: Crepe myrtles bloom on new wood, so prune them in late winter or early spring to increase next summer’s flower production. Pruning off old flowers in summer before they set seed may produce a second wave of blooms. Except on dwarf types, remove side branches on trunks up to the 4- to 5-foot level. To reveal attractive trunks, also remove branches growing inward toward center of plant.