Crape Myrtle Diseases: Symptoms and Treatment

Crape Myrtle Diseases and Pests: Black Leaves, White Powder, Aphids, Bark Scale

Your crape myrtle was planted for months of brilliant flowers, handsome foliage, colorful fall leaves, and beautifully exfoliating bark. Then something changes. The leaves turn black and sticky. White powder coats the new growth. Brown spots spread through the canopy. Tiny insects crowd beneath the leaves, or strange white bumps appear on the trunks.

The symptoms may look alarming, but they do not all point to the same problem. Black leaves are often coated with sooty mold growing on insect honeydew. White leaves may indicate powdery mildew, while white bumps on the bark suggest crape myrtle bark scale. Brown-spotted leaves that yellow and fall prematurely are more consistent with Cercospora leaf spot.

Correct identification matters because the treatments are completely different. A fungicide will not control aphids or bark scale. An insecticide will not cure powdery mildew. Washing black mold from the bark may improve appearances, but the mold will return if honeydew-producing insects remain active.

This guide helps you diagnose the most common crape myrtle diseases and pests, understand what the symptoms mean, decide when treatment is necessary, and prevent the same problem from returning.

Why Correct Diagnosis Matters

Several crape myrtle problems produce similar symptoms. Aphids and bark scale both excrete honeydew and cause sooty mold. Powdery mildew and bark scale are both white, but one coats leaves while the other forms individual waxy bumps on bark. Cercospora leaf spot and drought stress can both cause premature leaf drop.

Before reaching for a pesticide, inspect the affected plant closely:

• Are the leaves sticky?
• Is the white material powdery or made of separate bumps?
• Are insects present beneath the leaves?
• Are brown spots visible before the leaves turn yellow?
• Is the damage concentrated on foliage, flowers, or bark?
• Is the tree otherwise vigorous, or is it newly planted and stressed?

Quick Diagnostic Guide

Black Leaves on Crape Myrtle – Sooty Mold

Black leaves, trunks, or branches are usually covered with sooty mold. This dark fungal coating grows on honeydew, a sugary liquid excreted by sap-feeding insects.

Sooty mold does not normally infect the crape myrtle’s living tissue. It grows on the sticky surface created by aphids, crape myrtle bark scale, or occasionally another honeydew-producing pest. A heavy coating can reduce light reaching the leaves and spoil the appearance of the bark, but the insects are the primary problem.

Run a finger over an affected leaf. If it feels sticky beneath the black coating, inspect for:

• Aphids beneath the leaves and along tender shoots
• White felted scale insects on the trunks and branches
• Ants or wasps visiting the tree for honeydew
• Shiny droplets on leaves, pavement, furniture, or cars beneath the canopy

Aphids on Crape Myrtle

The crape myrtle aphid, Tinocallis kahawaluokalani, is a small, soft-bodied insect that gathers beneath leaves and along tender shoots. It is usually pale yellow-green with dark markings and may be difficult to notice until sticky honeydew begins falling from the canopy.

Light infestations usually cause little permanent harm. Heavy populations may curl young leaves, reduce vigor, and cover the plant and surrounding surfaces with honeydew and black sooty mold.

How to Manage Aphids

Begin with the least disruptive approach:

• Spray leaf undersides and shoot tips with a strong stream of water
• Allow lady beetles, lacewing larvae, hoverfly larvae, and other predators to work
• Avoid unnecessary nitrogen fertilizer that encourages excessive tender growth
• Use commercial insecticidal soap or horticultural oil if populations remain damaging

Soap and oil must contact the aphids directly to work. Thorough coverage is essential, and repeat treatment may be needed according to the label. Do not use household dish detergent as a substitute for a labeled insecticidal soap.

Crape Myrtle Bark Scale

Crape myrtle bark scale, Acanthococcus lagerstroemiae, is an invasive felt scale that feeds on trunks, branches, and twigs. Adult females are tiny and protected beneath white or gray felted wax.

Unlike aphids, which gather on leaves and tender growth, bark scale remains attached to woody tissue. Colonies commonly develop in branch crotches, bark crevices, old pruning wounds, and shaded areas beneath limbs.

Important clues include:

• Individual white or gray cottony bumps attached to bark
• Honeydew and extensive black sooty mold
• Pink or reddish fluid when a live female is crushed
• Reduced shoot growth or diminished flowering in heavy infestations
• White coverings that remain attached even after the insects have died

How to Treat Crape Myrtle Bark Scale

Wash and gently scrub accessible colonies with water and a soft brush. Preserve predatory lady beetles, including mealybug destroyers and other scale-feeding species.

Contact treatments work best against tiny pink crawlers before they develop protective wax. Double-sided sticky tape wrapped around a small infested branch can help detect crawler activity.

Dormant or delayed-dormant horticultural oil may suppress overwintering stages when the bark is covered thoroughly. Systemic products such as dinotefuran or imidacloprid are recommended in some regions for serious infestations, but guidance differs because of possible exposure to bees and other flower visitors. Follow local extension recommendations and the current product label.

White Powder on Crape Myrtle – Powdery Mildew

Powdery mildew is one of the most common crape myrtle diseases. It is caused by Erysiphe lagerstroemiae and appears as a white or gray powdery coating on leaves, tender shoots, flower buds, and flowers.

Young leaves may curl, pucker, twist, or remain stunted. Infected flower buds may develop poorly or fail to open, making early-season outbreaks far more damaging than a light coating on mature leaves late in the year.

The disease is favored by:

• Shade
• Poor air circulation
• Crowded growth
• Humid nights
• Mild, relatively dry daytime conditions
• Susceptible cultivars

Powdery mildew does not require wet foliage to infect. Full sun, good spacing, moderate fertilization, and resistant cultivars provide more reliable prevention than simply attempting to keep leaves dry.

How to Treat Powdery Mildew

Remove infected basal suckers and a few badly affected shoots, but do not strip the canopy. Improve sunlight and airflow without topping the tree.

A light late-season outbreak on a mature, vigorous plant may not require fungicide treatment. When mildew appears early, spreads rapidly, or coats flower buds, apply a product labeled for powdery mildew on ornamental trees at the first signs of disease.

Depending on the product label, active ingredients may include myclobutanil, propiconazole, thiophanate-methyl, copper, sulfur, horticultural oil, neem-based fungicides, or potassium bicarbonate. Do not combine oil and sulfur unless both labels specifically permit the mixture and timing.

Copper and sulfur can injure sensitive foliage under certain weather conditions. Test an unfamiliar product on a small area when directed by the label, and discontinue use if scorching, spotting, or distortion develops.

Brown Spots and Falling Leaves – Cercospora Leaf Spot

Cercospora leaf spot commonly becomes noticeable during warm, moist weather later in the growing season. It is caused by Cercospora lythracearum. Small yellow, tan, brown, or dark spots develop on the foliage, often beginning in the lower or interior canopy. White-gray fungal growth may be visible on the undersides of affected leaves.

Cercospora leaf spot rarely kills an established crape myrtle, but repeated severe defoliation reduces ornamental quality and may weaken young or stressed plants.

How to Manage Cercospora Leaf Spot

• Remove fallen infected leaves where practical
• Provide full sun and adequate spacing
• Avoid excessive nitrogen fertilization
• Water at the root zone rather than repeatedly wetting the canopy late in the day
• Select resistant cultivars for new plantings
• Consider a labeled fungicide when severe disease recurs annually

Fungicides protect uninfected foliage better than they restore spotted leaves. Preventive applications must begin before extensive symptoms and may require repetition according to the label.

Japanese Beetles and Skeletonized Leaves

Japanese beetles are metallic green and copper-colored insects that feed openly during summer. They chew the soft tissue between leaf veins, leaving a lacy or skeletonized appearance.

Small numbers can often be removed by hand early in the morning and dropped into soapy water. On established crape myrtles, moderate feeding is usually cosmetic and temporary.

Avoid Japanese beetle traps beside valuable plants. The floral lure can attract more beetles into the immediate area than the trap captures. If traps are used for monitoring, position them well away from the plants being protected.

Environmental Problems That Mimic Disease

Not every yellow, wilted, or dropping leaf is caused by a pathogen or insect. Crape myrtles may show similar symptoms when affected by:

• Drought or irregular watering
• Waterlogged soil and poor drainage
• Cold injury
• Transplant shock
• Excessive fertilizer
• Herbicide drift
• Root damage
• Severe topping or improper pruning

Examine the pattern. Disease and insects often create characteristic spots, coatings, feeding damage, or visible pests. Environmental stress may affect entire branches or the whole plant more uniformly.

How to Prevent Crape Myrtle Diseases and Pests

Healthy crape myrtles are not immune, but correct planting and care reduce both disease pressure and the need for pesticides.

• Plant in full sun: At least 6 hours of direct sun, with 8 hours supporting stronger flowering and lower mildew pressure
• Choose the right size: Give the cultivar enough room to reach its mature height and width
• Provide airflow: Avoid crowding the canopy against buildings, fences, and larger plants
• Water deeply: Support healthy roots without keeping the soil constantly saturated
• Avoid excess nitrogen: Lush, soft growth can attract aphids and increase disease susceptibility
• Remove unwanted suckers: Dense basal growth can harbor mildew and insects
• Inspect regularly: Look beneath leaves, around branch unions, and along the trunks
• Protect beneficial insects: Use broad-spectrum pesticides only when necessary
• Select resistant cultivars: Resistance is the best long-term defense against recurring fungal disease

Browse crape myrtle varieties to compare mature size, hardiness, flower color, and disease resistance before planting.

When Should You Call a Professional?

Contact a qualified arborist, plant-health professional, or local extension service when:

• The tree is too tall to inspect or treat safely from the ground
• Black mold returns despite repeated cleaning
• You cannot distinguish bark scale from another white bark growth
• The tree has major dieback, bark damage, or structural problems
• Severe defoliation occurs year after year
• Repeated pesticide treatments have not solved the problem
• The canopy is near electrical lines, buildings, vehicles, or waterways

Do not spray a tall canopy from a ladder. Professional equipment may be necessary to achieve safe coverage while minimizing drift and exposure to people, neighboring plants, and pollinators.

The Bottom Line

Most crape myrtle problems become easier to manage once the symptom is translated into the correct diagnosis. Black, sticky leaves usually indicate sooty mold caused by aphids or bark scale. White powder on foliage and buds points to powdery mildew. White felted bumps on trunks indicate bark scale, while brown spots and premature leaf drop suggest Cercospora.

Begin with inspection rather than automatic spraying. Protect beneficial insects, improve growing conditions, tolerate minor cosmetic damage when appropriate, and reserve pesticides for correctly identified problems that justify treatment.

Frequently Asked Questions

References

Updated: July 2026 • Reviewed by Gardenia Editors