Crepe Myrtle Bark Scale Is Spreading: How to Kill It, Clear Sooty Mold, and Prevent Powdery Mildew
Bark scale has overtaken powdery mildew as the top crepe myrtle threat. Identify it with the pink bleed test, treat pre-bloom with a soil drench, and pick resistant varieties to prevent powdery mildew for good.
If your crepe myrtle has turned black, you’re dealing with an invader that didn’t exist in the US twenty years ago.
Crepe myrtle bark scale arrived in a Texas nursery in 2004. By 2016, researchers confirmed it in twelve states. Today it’s established across the Southeast and still expanding northward into Virginia, the Carolinas, and beyond. The white crust on the trunk, the sooty black coating on every leaf — that’s bark scale at work, and it’s now the most urgent crepe myrtle problem for most US gardeners, having overtaken powdery mildew as the primary concern for anyone east of Texas.
This guide covers all three major crepe myrtle problems — bark scale, the sooty mold it triggers, and powdery mildew — with a diagnostic table so you can tell them apart and exactly what to do about each one.
Quick Diagnosis: What’s Wrong with Your Crepe Myrtle?
| What you see | Most likely cause | Section to read |
|---|---|---|
| Black coating on leaves, trunk, and limbs | Bark scale (sooty mold from honeydew) | Sections 2–4 |
| White or gray waxy crust on bark and twigs | Bark scale | Section 2 |
| White powdery coating on leaves and shoots | Powdery mildew | Section 5 |
| Tiny pale-green insects under leaves | Crepe myrtle aphids (also cause sooty mold) | Section 6 |
| Yellow spots on leaves with early drop | Cercospora leaf spot | Section 6 |
| Few or no blooms | Bark scale, insufficient sunlight, or pruning damage | Sections 2 and 6 |
Crepe Myrtle Bark Scale: The New #1 Threat
What It Is and How It Got Here
Crepe myrtle bark scale (Acanthococcus lagerstroemiae) is a soft scale insect native to Asia. It was first confirmed in the US in 2004 at a nursery in Richardson, Texas — almost certainly introduced through infested plant stock in the nursery trade. By August 2016, the peer-reviewed spread record documented it across twelve states including Alabama, Arkansas, Georgia, Louisiana, Mississippi, North Carolina, Oklahoma, Tennessee, and Virginia. It has since been confirmed in South Carolina and Pennsylvania.
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The visible sign is distinctive: a whitish-gray waxy crust matting the trunk, major limbs, and smaller twigs. Female scales measure roughly 2 millimeters — smaller than a sesame seed — and are immobile once they’ve settled. Males are winged but have no mouthparts and don’t feed. The tiny pink crawlers (newly hatched nymphs) are the mobile stage: they travel on wind, on birds, on gardening tools, and on clothing if you brush an infested tree.
The pink bleed test: If you’re not sure whether you’re looking at bark scale, lichen, or another coating, scrape a scale with your fingernail. Live bark scale bleeds a pinkish-red fluid. Dead scales and lichen leave no fluid at all. This is the fastest field test available, and it also confirms whether your treatment has been effective afterward.
Why Bark Scale Causes Sooty Mold — and Why the Mold Doesn’t Clear Quickly
The black coating isn’t the scale itself. It’s sooty mold, a fungus, and understanding the mechanism matters for treatment planning.
Bark scale nymphs feed on phloem sap — the sugary fluid that transports carbohydrates through the bark. They take in more sugar than they can metabolize and excrete the excess as honeydew, a sticky liquid that coats bark, leaves, and anything beneath the canopy. Sooty mold fungi colonize this honeydew as a food source. The fungus isn’t attacking plant tissue directly, but it coats leaf surfaces and blocks sunlight, reducing photosynthesis. In severe multiyear infestations, this contributes to branch dieback and reduced bloom.
The critical point for treatment planning: killing the scale doesn’t immediately remove the mold. Sooty mold persists on bark and leaves even after the honeydew source stops. It fades as new growth emerges and rainfall gradually washes old surfaces clean, but physical removal after treatment speeds recovery significantly.
Lifecycle: Why Populations Build So Fast
A single female bark scale produces between 100 and 320 eggs in her lifetime, laid in a protective ovisac on the bark. In the southeastern US, two to four generations complete each year depending on climate — with the primary crawler emergence running April through May and a second peak in late summer. Crawlers from these hatches can spread to adjacent trees even hundreds of feet away on the wind.
Lady beetles — including the twice-stabbed and multicolored Asian lady beetle — do prey on bark scale, and their populations often follow scale populations upward over time. But according to Mississippi State University Extension, natural predator populations can’t keep pace with bark scale reproduction under current infestation conditions in the US. Biological control alone is not a reliable management strategy at this stage of the invasion.
Treating Bark Scale: A Method That Protects Pollinators
Systemic Soil Drench: The Primary Treatment
The most effective treatment is a systemic neonicotinoid insecticide applied as a soil drench between late March and May. The insecticide absorbs through roots, enters the phloem sap the scales are feeding on, and kills them from the inside. Treating through the soil rather than as a foliar spray also dramatically reduces pollinator exposure — bees encounter insecticide at much lower concentrations from a soil drench than from insecticide-coated pollen or foliage.
Three active ingredients are labeled and effective:
- Dinotefuran (Greenlight Tree and Shrub Insect Control with Safari, or commercial Safari 20 SG) — fastest-acting and most effective in extension trials
- Imidacloprid (BioAdvanced Tree & Shrub Insect Control, Merit) — widely available at garden centers; apply once per season
- Thiamethoxam (Meridian) — effective but primarily in commercial formulations
Homeowner rate example for a 1.47% imidacloprid product: 1 fl oz per inch of trunk circumference, applied as a soil drench after raking mulch away from the base. Always check your specific product label — concentration varies between brands and the application rate changes accordingly. Water in thoroughly after applying, then replace the mulch.
One drench handles the full season. Plan to repeat the following spring even if the tree looks clean — eggs overwinter in bark and crawlers will re-emerge in April regardless of how last season went.
Pollinator timing: Neonicotinoids applied to soil can move into pollen and nectar once the tree blooms. According to NC State Extension, imidacloprid applied as a soil drench may contaminate flower parts that bees visit. Apply during the late March to May window, before your tree blooms, to maximize treatment efficacy while minimizing pollinator risk. Never apply systemic insecticides to a crepe myrtle that is actively flowering.
Contact Sprays: Useful During Crawler Emergence
As a supplement to the soil drench — not a replacement — contact sprays applied during crawler emergence periods reduce populations faster than waiting for the systemic treatment to take full effect.
- Dormant oil applied after leaf fall and before spring bud break smothers overwintering eggs and settled nymphs. Safest for pollinators since the tree isn’t in bloom.
- Bifenthrin + 2% horticultural oil: apply only when temperatures are between 45–90°F, no rain is forecast for 24 hours, and always in very late evening when pollinators have stopped foraging. Most effective contact combination but carries higher non-target insect risk.
- Insect growth regulators (pyriproxyfen or buprofezin): lower risk to beneficial insects than pyrethroids; apply in 14-to-21-day intervals during crawler periods.
Monitoring crawler hatch: Wrap double-sided sticky tape around a small branch in mid-April and check every few days. When you see pink specks stuck to the tape, crawlers are actively hatching and contact spray will hit them at their most vulnerable stage.
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For trees where bark scale covers the full trunk-to-canopy and cosmetic recovery within one season isn’t realistic, Clemson Cooperative Extension recommends cutting the tree flush to the ground. Bag all removed material in household garbage bags — never compost it, because crawlers spread from yard-waste piles and compost heaps. Allow regrowth from the stump, selecting three evenly spaced new shoots as scaffold branches. With twice-yearly fertilization, most trees return to blooming size within three years.
Getting Rid of Sooty Mold After You’ve Treated the Scale
With the scale under control and honeydew production dropping, sooty mold stops accumulating. But old mold on trunks and larger branches won’t clear on its own within weeks. For faster cosmetic recovery:
- Scrub the trunk and main scaffold branches with a soft brush and warm soapy water — Clemson recommends 4 oz of dish soap per gallon of water. This physically removes the mold without damaging bark.
- Pressure washing works well on the main trunk; avoid directing the stream at new buds or growing tips.
- Sooty mold on leaves typically clears when old foliage drops at the end of the season. Focus cleaning effort on permanent wood.
Cleaning mold before treating scale is largely wasted effort — the honeydew source will recoat cleaned surfaces within weeks. Treat scale first, clean mold after.
Powdery Mildew: The Classic Crepe Myrtle Disease
Before bark scale arrived, powdery mildew (Erysiphe lagerstroemiae) was the crepe myrtle problem most gardeners worried about. It’s still common on susceptible varieties in warm, humid conditions with poor air circulation.
Identification: White to grayish powdery growth on leaves, flower buds, and new shoots. Infected flower buds often fail to open. Affected shoots become stunted and distorted. The key visual difference from bark scale and sooty mold: powdery mildew is always white or gray while sooty mold is always black.
Treatment: Fungicides containing myclobutanil, propiconazole, thiophanate-methyl, or copper-based products provide control. Multiple applications through the growing season are typically needed on susceptible varieties. But chemical treatment is fighting symptoms — if you’re treating the same tree for mildew year after year, the real answer is variety replacement.
If you’re curious about when your crepe myrtle should bloom, severe powdery mildew is one of the reasons buds fail to open on time or at all.
The lasting solution is choosing a resistant variety. Clemson Cooperative Extension rates these cultivars as having very good to total powdery mildew resistance:
| Resistance level | Varieties |
|---|---|
| Total resistance | ‘Apalachee’, ‘Fantasy’ |
| Very good resistance | ‘Caddo’, ‘Hopi’, ‘Miami’, ‘Osage’, ‘Pecos’, ‘Regal Red’, ‘Sioux’, ‘Tonto’, ‘Tuscarora’, ‘Tuskegee’, ‘Wichita’ |
‘Tonto’ and ‘Tuscarora’ also show good resistance to Cercospora leaf spot, making them strong all-around choices for humid climates where multiple fungal problems are common.
Other Crepe Myrtle Problems Worth Knowing
Crepe myrtle aphids (Tinocallis kahawaluokalani) are pale yellowish-green, 1/16 to 1/8 inch long, and cluster on the undersides of leaves. Like bark scale, they produce honeydew that feeds sooty mold — but aphid-driven sooty mold appears primarily on leaves rather than bark, which helps with diagnosis. Natural predators cycle aphid populations more effectively here than they do with bark scale. A strong water spray dislodges colonies; repeat as needed. Systemic imidacloprid soil drench controls severe infestations.
Cercospora leaf spot produces yellow spots between 1/8 and 1/4 inch across on the upper leaf surface with white-gray fungal growth on the underside, causing premature leaf drop. The same fungicides used for powdery mildew (thiophanate-methyl or myclobutanil) provide control. ‘Fantasy’, ‘Tonto’, and ‘Tuscarora’ are resistant to both diseases.
Poor flowering is often cultural rather than disease-related. Crepe myrtles need a minimum of 8 hours of direct sun per day for reliable bloom. Over-pruning through heavy topping — sometimes called “crape murder” — removes established flowering wood and forces the tree to grow non-blooming replacement stems for one or two seasons. If heavy-handed pruning is what you’re dealing with, the crepe myrtle pruning guide covers how topping damage develops and how to restore the tree’s natural branching structure over time.
Prevention: What You Can Do Before Problems Start
No crepe myrtle variety has been confirmed resistant to bark scale, so prevention centers on cultural controls and early detection:
- Plant in full sun. Shaded trees show higher crawler populations than full-sun trees. Eight hours of direct sun also reduces conditions favorable to powdery mildew.
- Buy pest-free stock. Bark scale entered the US through infested nursery plants. Before purchasing any new crepe myrtle, inspect the trunk and branches closely for white waxy crust or pinkish egg masses under the scales.
- Check secondary hosts. Bark scale spreads to spirea, American beautyberry, hypericum, pomegranate, fig, and privet growing near infested trees. Treating your crepe myrtles while leaving infested secondary hosts in place guarantees re-infestation. Survey and treat the whole landscape as a unit.
- Monitor from April onward. Sticky tape traps placed on small branches in early April catch the first crawler emergence and give you lead time before the population builds. Earlier treatment is cheaper and more effective than waiting for visible infestation to declare itself.
For more on what makes crepe myrtles resilient plants worth protecting, see the essential facts about lagerstroemia covering their biology and heat tolerance.
Frequently Asked Questions
Can bark scale kill my crepe myrtle?
Trees rarely die quickly from bark scale. The realistic outcome of untreated infestation is reduced vigor, fewer and smaller blooms, and severe aesthetic damage from sooty mold. Left untreated for multiple years, heavy infestations can contribute to branch dieback. Treatment is worth doing for tree health, not just appearances.
Can I just wash the black mold off without treating the scale?
You can remove existing sooty mold with soapy water, but the honeydew source is still active. Within weeks, new mold recoats the cleaned surfaces. Treat scale first — sooty mold is a symptom of the underlying infestation, not the disease itself.
I have both bark scale and powdery mildew. Which do I treat first?
Bark scale first. Powdery mildew is manageable with fungicide at almost any point in the season. Bark scale has a narrow treatment window — late March to May — and missing it means waiting another year for optimal systemic treatment. Address scale in spring, then manage mildew through the growing season as needed.
Is it safe to use systemic insecticides near my vegetable garden?
Soil-applied neonicotinoids can move into nearby soil and into untargeted flowering plants within the drip zone. Keep applications within the drip line of the target tree and avoid applying near vegetable beds or pollinator-focused plantings. Timing before bloom also minimizes risk to bees visiting the treated tree itself.
Can I use neem oil instead of a systemic drench?
Neem oil and horticultural oils can suppress crawler emergence and reduce overwintering populations when used as a dormant spray before bud break. They’re not reliably effective as a standalone replacement for systemic treatment on established infestations. Use dormant oil in winter to reduce overwintering populations, then follow with a systemic soil drench in spring.
Sources
[1] Rong Sun, Scott D. Johnson, & Bin Xu. “Crapemyrtle Bark Scale: A New Threat for Crapemyrtles, a Popular Landscape Plant in the US.” Journal of Integrated Pest Management, NCBI PMC, 2016.
[2] Mississippi State University Extension. “Crape Myrtle Bark Scale: Identification and Control.”
[3] Clemson Cooperative Extension. “Crapemyrtle Bark Scale.” Home & Garden Information Center.
[4] University of Arkansas Cooperative Extension. “Crapemyrtle Bark Scale.”
[5] NC State Extension. “Biology and Management of Crape Myrtle Bark Scale for Homeowners.”
[6] Virginia Cooperative Extension / Henrico County. “Crape-Myrtle Bark Scale.”
[7] Clemson Cooperative Extension. “Crape Myrtle Diseases & Insect Pests in South Carolina.” Home & Garden Information Center.
