Crepe Myrtle Diseases and Pests: Bark Scale, Powdery Mildew, and the Rest

Crepe myrtles (Lagerstroemia indica and the L. indica × L. fauriei hybrids) used to be one of the lowest-maintenance ornamental trees in Southern landscapes. Then 2004 happened. Crepe myrtle bark scale, an invasive insect from Asia, arrived in Texas and started spreading. Twenty years later it has reached most of the Southeast and parts of the mid-Atlantic, and it has changed the management calculus for every crepe myrtle in those regions.

Five problems account for most of what goes wrong on backyard crepe myrtles: crepe myrtle bark scale (the new big one), powdery mildew, Cercospora leaf spot, sooty mold (which is a symptom of the scale or aphid problem, not a primary disease), and root rot. Three of the five have direct cultural and chemical fixes. The fifth (sooty mold) goes away on its own once you solve the insect that’s producing the honeydew it grows on.

This guide covers all five plus a note on the “crepe murder” pruning question, which gets tangled up with disease management because hard-pruned trees are more susceptible to scale and mildew.

How to tell which problem you’re looking at

Quick visual triage. Match the most obvious symptom and jump to the section below.

• White or gray waxy crusts on bark, branches, and trunks, with black sticky honeydew underneath: crepe myrtle bark scale
• White powdery coating on new leaves and flower buds, distorted growth: powdery mildew
• Dark brown irregular spots on lower leaves, premature yellowing and drop in mid-to-late summer: Cercospora leaf spot
• Black sooty coating on leaves and bark, sticky honeydew dripping from canopy: sooty mold (a downstream symptom)
• Whole branches wilting, leaves dropping early, decline of an established tree: possible root rot or Phytophthora

Most crepe myrtle problems in the Southeast now trace back to bark scale and the secondary sooty mold it causes. In the South Atlantic and Gulf states, scale management has become the primary maintenance task on crepe myrtles. Outside those regions, powdery mildew and leaf spot remain the dominant disease issues.

Crepe myrtle bark scale

Crepe myrtle bark scale (Acanthococcus lagerstroemiae, formerly Eriococcus lagerstroemiae) is the most important new pest in this guide. Per Clemson HGIC and Texas A&M AgriLife research, the scale was first detected in Texas in 2004 and has since spread through Oklahoma, Arkansas, Louisiana, Mississippi, Georgia, North Carolina, Virginia, and South Carolina (confirmed in 2019). It continues to spread north and west.

What it looks like

White or gray waxy crusts on the bark of trunks, branches, and twigs. The crusts are the female scale insects covered with their protective wax filaments. They tend to congregate in branch crotches and at old pruning cut sites, especially the upper portion of crepe murder cuts where the bark has been stressed.

If you crush one of the white crusts with your fingernail, a pink fluid comes out, which is the eggs. That pink-on-finger test is diagnostic. No other scale on crepe myrtle has this color.

Downstream symptoms include:

• Black sooty mold coating leaves, lower branches, fence rails, decks, parked cars, and anything else under the tree
• Reduced flowering: scale-infested trees often produce smaller and fewer flower panicles
• Delayed leaf emergence in spring
• Premature bark peeling on heavily infested plants

Why it happens

Females produce 60-250 eggs per ovisac. The crawlers (newly hatched scales) are pink, less than a millimeter long, and move during a brief window before settling permanently. Peak crawler emergence happens mid-to-late April through May, with a second peak in late summer. Crawlers can spread between plants via wind, animals, garden tools, and even on clothing.

The pest has no significant natural enemies in North America. Without active management, scale populations build year over year until the tree is completely encrusted.

What to do about it

A combination approach works better than any single treatment.

• Soil drench with a systemic insecticide in early spring (March in the South). Dinotefuran (the active ingredient in some commercial Greenlight and Safari products) is the most effective. The systemic uptake reaches the bark where the scale feeds, killing the insects from the inside.
• Bark spray with horticultural oil + bifenthrin during crawler emergence (mid-April through May). Smother the visible crusts and kill the active crawlers in a single application. Bonide Neem Oil concentrate mixed per label as a 2% horticultural oil works in lieu of bifenthrin for organic-minded growers, but the bifenthrin combination is more effective on heavy infestations.
• Scrub the trunk with soapy water to physically remove visible scale and ovisacs before chemical treatment. A stiff brush works on smooth bark. This step alone reduces populations by 50%+ on lightly infested trees.
• Plant in full sun. Shaded trees host more scale.

For severely infested trees, the LSU AgCenter sometimes recommends cutting the tree to the ground in late winter and letting it regrow from the roots. Crepe myrtles regrow vigorously, and you start over with a clean tree. This is the same nuclear option you’d use for a tree that’s been crepe-murdered for ten years and never recovered: cut to ground, let it sucker, select 3-5 strong leaders, and you have a healthy small tree in 3-4 years.

How to keep it from coming back

• Don’t share crepe myrtle cuttings with neighbors during scale season. Crawlers ride on plant material.
• Inspect new nursery stock before bringing it home. Look for white waxy crusts on the lower branches.
• Annual soil drench in March on previously infested trees, even if the population looks suppressed.
• Avoid heavy pruning. Each pruning cut creates a stress site where scale congregates the following season.

Powdery mildew

Powdery mildew is the classic crepe myrtle disease and the one that drove plant breeders to develop the modern resistant cultivars. Caused primarily by Erysiphe lagerstroemiae, it shows up as a white powdery coating on new leaves and flower buds, often distorting the growth and reducing the flower display.

What it looks like

White, almost flour-like coating on the upper surface of new leaves. Affected leaves often curl, turn purple or red along the edges, and may drop early. On flower buds, mildew prevents normal opening, producing distorted, half-formed blooms. The disease is worst on new growth and during periods of warm days with cool damp nights.

Why it happens

The fungus overwinters in dormant buds and on bark surfaces. Spring temperatures around 70-85°F, combined with high humidity at night, create ideal conditions. Shaded sites and crowded plantings get hit worst because air doesn’t move through the canopy to dry the leaves.

Cultivar resistance varies dramatically:

• Highly resistant: The U.S. National Arboretum’s L. indica × L. fauriei hybrids, often called the “Native American Tribe” series. Examples include Natchez (white), Muskogee (lavender), Tuscarora (coral pink), Acoma (white, cascading), Hopi (medium pink), Tonto (red), Sioux (dark pink), Catawba (purple), Pecos (pink), Yuma (lavender).
• Moderately resistant: many newer indica-only releases bred for mildew resistance.
• Highly susceptible: older indica varieties like Watermelon Red, Carolina Beauty, and many of the unnamed cultivars sold cheaply at big-box stores.

What to do about it

• Plant resistant cultivars at the start. Single highest-leverage intervention. A Natchez or Tuscarora needs almost no spraying for mildew.
• Site for full sun and good air movement. Mildew thrives in shade.
• Neem oil applications at the first sign of symptoms. Bonide Neem Oil concentrate at label rate, sprayed every 7-14 days through the growing season, suppresses active infections. Spray the underside of leaves.
• Don’t over-fertilize. Lush succulent new growth is mildew’s favorite target.
• Avoid overhead irrigation. Drip or basin water at the root zone.

Cercospora leaf spot

Cercospora leaf spot (Cercospora lythracearum) shows up in mid-to-late summer, especially during wet weather. It produces dark brown irregular spots without a yellow halo, mostly on the older lower leaves first, then progressing upward.

What it looks like

Small (1/4 inch or less) dark brown angular spots on leaves, mostly on the lower canopy. Spots may coalesce into larger blotches. Heavy infections cause yellowing and premature leaf drop in August and September, which weakens the tree heading into winter.

Why it happens

The fungus overwinters in fallen leaves. Spring rains release spores that infect new growth. Cool wet weather drives the worst outbreaks. The disease is most common in the humid Southeast and along the Gulf Coast.

What to do about it

• Rake fallen leaves in autumn. Reduces next year’s spore source significantly.
• Improve air circulation by selective thinning of interior branches in late winter.
• Avoid overhead watering at dusk.
• Copper fungicide at the first sign of symptoms can suppress new infections. Application timing: at first appearance of leaf spots, then every 14 days until cool dry weather returns.
• For severe recurring cases, myclobutanil, propiconazole, or chlorothalonil applied per label are more effective than copper but cost more.

For most backyard crepe myrtles, Cercospora is annoying rather than dangerous. The tree drops leaves a few weeks early and recovers fully the following spring.

Sooty mold

Sooty mold isn’t a disease in the strict sense. It’s a secondary fungus that grows on the honeydew excreted by sap-sucking insects. On crepe myrtles, that’s most often crepe myrtle bark scale (covered above), or sometimes crepe myrtle aphids (Tinocallis kahawaluokalani).

What it looks like

A flat black coating on leaves, bark, and any surface underneath the tree. The mold doesn’t penetrate plant tissue. It just grows on the sticky sugary honeydew. The tree looks dramatically dirty, but the mold itself does little direct damage. The underlying insect is the problem.

What to do about it

Solve the insect problem and the mold disappears on its own within a few weeks of the insects being eliminated. For crepe myrtle bark scale, follow the protocol above. For aphids, Bonide Neem Oil sprayed on the leaves and underside of leaves at the first sign of aphids handles most populations. Heavy aphid populations may also benefit from a soil drench with imidacloprid or dinotefuran.

For visible cleanup of established sooty mold, a gentle spray with the garden hose removes the deposits once the underlying insect is gone. The mold sloughs off naturally as the affected leaves age and drop.

Root rot

Root rot in crepe myrtles is uncommon but serious when it appears. The most likely pathogens are Phytophthora species (water molds) and Armillaria (honey fungus). Both attack the root system and cause progressive decline.

What it looks like

• Sudden wilting on one or more branches
• Leaves turning yellow and dropping early
• Sparse smaller flowers compared to prior years
• Mushrooms or fungal fruiting bodies near the trunk base (especially Armillaria)
• Soft, dark, decayed roots when you dig down and expose them
• White fungal mat under the bark at the soil line (Armillaria signature)

By the time above-ground symptoms appear, the root system has often lost 50% or more of its absorbing capacity.

Why it happens

Phytophthora root rot needs moist soil and poor drainage. Crepe myrtles planted in heavy clay soil with seasonal standing water are the typical victims. Armillaria roots are often present in soils where another tree died years ago, especially if the previous tree was a stone fruit or oak; the fungus colonizes the dead wood and waits for new host roots to encounter it.

What to do about it

Once root rot is established, the tree usually doesn’t recover. Catching it early allows for some intervention:

• Check drainage by digging a 1-foot test hole, filling with water, and timing how long it takes to drain. Less than 4 hours is good. More than a day means the site is too wet.
• Improve drainage with raised mounds, French drains, or careful regrading. None of these is easy on an existing tree, but they help if you’re replanting.
• Reduce irrigation if you’ve been overwatering. Crepe myrtles need far less summer water than most homeowners give them.
• Fungicide drenches with fosetyl-al or mefenoxam can suppress active Phytophthora infections. They don’t help against Armillaria.

For Armillaria specifically, the practical advice is to plant something less susceptible in the same location after removing the dead tree. Resistant species include hollies, junipers, and many evergreens.

A note on “crepe murder” and disease

The annual practice of topping crepe myrtles severely (“crepe murder”) creates large wounds and clusters of weak adventitious growth from the cut sites. Those wounds are exactly where crepe myrtle bark scale prefers to congregate, and the weak watersprouts that emerge from improper pruning cuts attract aphids in disproportionate numbers.

The correct annual maintenance, covered in our crepe myrtle trimming guide, removes seed heads and crossing branches without taking off the main scaffolds. A properly maintained crepe myrtle has fewer pruning wounds, less stress, and significantly lower scale and aphid pressure than a topped tree.

If you’ve inherited a tree that’s been crepe-murdered for years, the cleanest restart is to cut the entire trunk back to within 6-12 inches of the ground in late winter, then select 3-5 of the strongest new shoots and train them into the new scaffolding over the next 2-3 years. This sounds severe but produces a much better tree than continued annual topping.

When to call an arborist

Most crepe myrtle problems are home-garden manageable. Two situations warrant professional help.

First, suspected root rot or Armillaria infection on a mature established tree where decisions about removal versus aggressive intervention matter financially. Second, severe crepe myrtle bark scale infestation on multiple trees in the landscape where coordinated treatment timing across the property matters.

An ISA-certified arborist consultation runs $75-200 in most US markets. Find one through the Trees Are Good arborist locator or read our guide to what an arborist does before you call.

If the tree is past saving, tree removal on a mature crepe myrtle typically runs $250-1,200, lower than most landscape trees because they’re small and stump removal is uncomplicated.

Prevention checklist

Seven habits handle most crepe myrtle problems:

• Plant resistant cultivars. For new plantings in the South, the L. indica × L. fauriei hybrids (Natchez, Muskogee, Tuscarora, Acoma, Hopi, Tonto, Sioux, Catawba) resist powdery mildew, tolerate Cercospora leaf spot, and (so far) seem somewhat less susceptible to bark scale than the pure indica cultivars.
• Full sun. Crepe myrtles need 6+ hours of direct sun. Shaded plants get more disease and host more pests.
• Well-drained soil. Crepe myrtles tolerate heat and drought, but they don’t tolerate wet feet. Plant on raised mounds in heavy clay.
• Drip irrigation at the root zone. No overhead spray during summer humidity.
• Annual late-winter cleanup. Remove seed heads, crossing branches, and any visible bark scale crusts. Do NOT top the tree.
• Soil drench in March for scale prevention on trees in CMBS-active regions (Southeast, Gulf states, mid-Atlantic).
• Rake fallen leaves in autumn to reduce Cercospora overwintering spore loads.

For broader fungal disease patterns across the rest of your yard, see our tree fungus guide. Other small ornamentals that share crepe myrtle’s role in the landscape (or could replace a scale-damaged tree) are covered in the flowering trees roundup. Texas-specific cultivar guidance lives in the flowering trees in Texas guide, which focuses on species best adapted to the heat and drought conditions there.

Frequently asked questions

What is the most damaging crepe myrtle pest?

Crepe myrtle bark scale (Acanthococcus lagerstroemiae) is the most damaging in the regions where it has established (most of the Southeast since 2004). Powdery mildew is the most common cosmetic issue on susceptible cultivars. Sooty mold is the most visually dramatic but is a downstream symptom of scale or aphids rather than a primary disease.

How do I get rid of crepe myrtle bark scale?

Combination treatment works best. Scrub visible white crusts off the bark with soapy water in early spring. Apply a soil drench with dinotefuran or imidacloprid in March. Spray the trunk and branches with horticultural oil plus bifenthrin during crawler emergence (mid-April through May). Repeat annually in heavily infested regions.

Why is my crepe myrtle covered in black soot?

That’s sooty mold growing on honeydew from crepe myrtle bark scale or crepe myrtle aphids. The mold itself doesn’t damage the tree, but the underlying insect is sapping the tree’s energy and reducing flowering. Treat the insect (scale or aphids), and the mold disappears on its own within weeks.

Should I top my crepe myrtle to control disease?

No. “Crepe murder” creates wounds where bark scale congregates and weak watersprouts that attract aphids. Disease management is significantly easier on properly trained crepe myrtles. If your tree has been topped for years and looks bad, the cleanest restart is to cut it to within 6-12 inches of the ground in late winter and select strong new shoots as the future scaffolding.

What crepe myrtle cultivars resist disease best?

The U.S. National Arboretum hybrids (interspecific crosses between Lagerstroemia indica and L. fauriei), often called the “Native American Tribe” series, are the most disease-resistant. The best-known cultivars include Natchez (white flowers, 30 feet tall), Muskogee (lavender flowers, 24 feet), Tuscarora (coral pink, 16 feet), Acoma (white, weeping habit), Hopi (medium pink), Tonto (red), Sioux (dark pink), and Catawba (purple). These resist powdery mildew, tolerate Cercospora, and tend to perform better against bark scale than pure indica varieties.

When should I spray my crepe myrtle?

Two main timing windows. In March, soil drench with a systemic insecticide for bark scale prevention. In mid-April through May, spray horticultural oil plus bifenthrin (or neem oil for organic) on the trunk and branches during crawler emergence. For powdery mildew, spot-treat with neem at first symptoms. For Cercospora, copper applications at first leaf spots can suppress further spread. A clean cultivar in a sunny well-drained site rarely needs more than one or two of these interventions per year.

Are crepe myrtle pests contagious to other trees?

Crepe myrtle bark scale has been found in low numbers on other plants (boxwood, persimmon, some pomegranate cultivars) but reproduces successfully only on crepe myrtles in landscape conditions. Powdery mildew and Cercospora are crepe-myrtle-specific species and don’t cross to other ornamentals. Sooty mold can grow on any plant with honeydew-producing insects, so adjacent landscape plants under heavy crepe myrtle scale infestation may show some sooty deposits from the dripping honeydew.

Will my crepe myrtle die from bark scale?

Heavy scale infestations rarely kill the tree outright, but they dramatically reduce flowering and aesthetic value, and the constant stress makes the tree more vulnerable to drought and other problems. After 5+ years of untreated heavy infestation, decline becomes serious. Most homeowners decide either to commit to annual treatment or to cut the tree to the ground and start over with clean shoots.