How to Get Rid of White Spots on Crepe Myrtle

White spots on crepe myrtle are almost always caused by one of two things: powdery mildew, a fungal disease that coats leaves and stems in a chalky white film, or crepe myrtle bark scale, an insect pest that leaves white, felt-like deposits on the bark. Both are treatable, but the approach differs depending on which problem you have. Telling them apart is the first step, and the fixes range from simple cultural adjustments to targeted sprays.

Powdery Mildew or Bark Scale

The two culprits look different and show up in different places on the tree. Powdery mildew appears as a white or grayish powder on the surfaces of leaves, flower buds, and young stems. It often starts on new growth and can spread rapidly in humid weather, eventually causing leaves to curl, distort, and wither. Under a microscope the fungus forms dense whitish colonies, but you do not need magnification to spot the problem: if the leaves look like someone dusted them with flour, it is powdery mildew.¹

Crepe myrtle bark scale (CMBS) looks nothing like powdery mildew up close, though from a distance both register as “something white on my tree.” Bark scale produces small white or gray waxy coverings glued to the bark, mainly on trunks and larger branches rather than on leaves. When you scrape one off with a fingernail, you will see a pinkish or lavender smear underneath, which is the insect’s body. Heavy infestations are accompanied by black sooty mold that grows on the sugary honeydew the insects excrete, so a crepe myrtle covered in both white patches on the bark and black residue on the stems and leaves is a strong sign of bark scale rather than a fungal disease.²

If you have white powder on leaves and young growth, skip ahead to the powdery mildew section. If you have white waxy bumps on the bark (especially with sooty mold), jump to the bark scale section. Some unlucky trees have both at once, in which case you will want to tackle each problem separately.

How to Get Rid of Powdery Mildew

Powdery mildew on crepe myrtle is caused by a fungus in the genus Erysiphe. It thrives in warm days, cool nights, and high humidity, and it tends to be worst on crowded, shaded trees where air does not move freely through the canopy. The good news is that powdery mildew rarely kills a crepe myrtle. The bad news is that it makes the tree look awful, stunts new growth, and can reduce flowering.

Cultural Fixes That Make the Biggest Difference

Before reaching for a spray bottle, start with the conditions that let powdery mildew take hold in the first place. Pruning is the single most useful cultural intervention. Thin interior branches so air flows through the canopy instead of stagnating. Remove crossing or inward-growing limbs, and clear away any suckers at the base. Better airflow lowers humidity around the leaves, which is the environmental factor the fungus depends on most.

Plant location matters too. Crepe myrtles in full sun develop far less powdery mildew than those tucked into partial shade. If you are planting a new tree, give it at least six to eight hours of direct sunlight. Overhead irrigation also encourages fungal problems. Water at the base of the tree rather than spraying the canopy, and water in the morning so leaves dry quickly.

Fungicide Options

When cultural fixes are not enough, fungicides can knock powdery mildew back. Several types are available at garden centers:

Neem oil: Works as both a fungicide and an insecticide. Apply as a foliar spray every seven to fourteen days during active infection. It is organic-approved and widely available.
Horticultural oil: Lightweight paraffinic oils smother fungal spores on contact. Apply early in the morning or late in the evening, never in full midday sun, to avoid leaf burn.
Synthetic fungicides: Products containing myclobutanil, propiconazole, or thiophanate-methyl are effective against Erysiphe species. These are best used preventively or at the first sign of white patches. Once the fungus has heavily colonized the leaves, fungicides slow the spread but will not undo existing damage.
Baking soda spray: A tablespoon of baking soda mixed with a gallon of water and a small amount of liquid soap can raise leaf-surface pH enough to inhibit spore germination. This is a mild remedy and works best as a supplement, not a standalone treatment.

Whichever product you use, thorough coverage is critical. The fungus lives on the leaf surface, so the spray needs to reach the tops and undersides of leaves as well as young stems. Repeat applications every one to two weeks during humid weather or whenever you see new white patches forming.

How to Get Rid of Crepe Myrtle Bark Scale

Bark scale is a newer problem in the United States and has caught many gardeners off guard. The insect first turned up in Texas and has since spread across much of the Southeast. Because the pest is relatively new, it sometimes goes unrecognized until an infestation is severe and the tree is caked in sooty mold. Treating bark scale involves a combination of physical removal, chemical control, and encouraging natural predators.

Scrubbing and Physical Removal

Start by physically removing as many scale insects as you can. Use a soft-bristled brush or cloth soaked in a diluted dish-soap solution and scrub the trunk and major limbs. This kills the insects on contact, removes the white waxy coverings, and washes away some of the sooty mold. Pressure washing the bark on a low setting also works for large trees. Physical removal will not eliminate the population entirely since crawlers (the tiny mobile juvenile stage) will recolonize, but it reduces numbers fast and makes chemical treatments more effective.

Chemical Treatments

For moderate to heavy infestations, insecticide treatment is usually necessary. The two most common approaches are soil drenches and contact sprays:

Soil drench with a systemic insecticide: Dinotefuran is the systemic most recommended for bark scale because it moves through the tree’s vascular system quickly, often reaching effective concentrations in the canopy within a few weeks. It is applied as a drench around the root zone. Imidacloprid works similarly but moves through the tree more slowly, sometimes taking several months to reach full effectiveness. Systemic treatments are best applied in spring when the tree is actively taking up water.
Contact sprays: Horticultural oil or insecticidal soap sprayed directly onto the bark during the crawler stage (typically late spring through early summer) can reduce populations without systemic chemicals. Timing matters because the waxy covering on mature scale insects physically shields them from contact sprays. You need to hit the crawlers, which are tiny, pinkish, and unprotected.

An integrated approach that considers timing, application rate, and the impact on pollinators and natural enemies produces better long-term results than relying on any one product alone.³ Systemic neonicotinoids like dinotefuran and imidacloprid can harm bees if applied during bloom, so the safest window for application is either well before flowering or after petals have dropped.

Encouraging Natural Predators

Several predatory insects feed on crepe myrtle bark scale. Lady beetles, particularly species in the genera Chilocorus and Hyperaspis, are among the most effective natural enemies found in the United States.³ Twice-stabbed lady beetles (Chilocorus species) are especially useful because they specialize in eating scale insects. If you spot small black lady beetles with two red spots on the bark of your crepe myrtle, leave them alone and avoid broad-spectrum insecticide sprays that would kill them.

You can also attract and retain beneficial insects by planting companion plants that provide nectar and pollen, and by limiting insecticide use to targeted products and specific timing windows. A yard that supports predator populations will experience lower bark scale pressure over time without repeated chemical inputs.

Cleaning Up Sooty Mold

Sooty mold is the black, soot-like coating that develops wherever honeydew from bark scale accumulates. It covers stems and, in severe cases, leaves, blocking sunlight and reducing the tree’s ability to photosynthesize.² The mold itself is not parasitic, meaning it does not infect the plant tissue. It simply grows on the sugary residue. Once you eliminate the bark scale and cut off the honeydew supply, sooty mold stops spreading and eventually weathers away.

To speed things up, you can wash sooty mold off with a strong spray of water or scrub it with a diluted soap solution. On smaller trees, a garden hose with a spray nozzle works well. On larger trees, a pressure washer on a gentle setting saves a lot of time. Some gardeners spray a mixture of horticultural oil and water onto the mold, which helps loosen it. The key insight is that sooty mold is a symptom, not a cause: if you treat only the mold and ignore the bark scale, it will come right back.

Why Keeping Your Tree Well-Fed Helps

Stressed, under-nourished crepe myrtles are more vulnerable to bark scale. Research comparing bark scale populations on crepe myrtles grown in different nutrient conditions found that the insect reproduced more successfully on nutrient-deficient plants. Trees grown in adequate nutrient solutions supported lower insect performance, with the pest’s population growth rate actually dipping below replacement level under good growing conditions.⁴

The practical takeaway is that a basic fertilizer program supports the tree’s defenses. Crepe myrtles are not heavy feeders, but an annual application of a balanced slow-release fertilizer in early spring gives the tree the nutrients it needs to push vigorous growth. Healthy growth also means thicker bark and a more robust canopy, both of which help the tree tolerate pests and diseases that would overwhelm a weaker specimen. Avoid over-fertilizing with nitrogen, though, because overly lush, soft new growth is more susceptible to powdery mildew.

Choosing Varieties That Resist White Spots

If you are planting a new crepe myrtle or replacing one that has been plagued by problems, variety selection can save you years of headaches. Resistance to powdery mildew varies enormously between cultivars. Interspecific hybrids, which are crosses between the common Lagerstroemia indica and the Japanese species Lagerstroemia fauriei, tend to have strong resistance. The popular cultivar Natchez, for example, is a white-flowered hybrid well known for resisting powdery mildew, while a pure L. indica cultivar like Carolina Beauty is highly susceptible.⁵

Other widely available mildew-resistant cultivars include Muskogee, Tuscarora, Tonto, Sioux, and most of the other “Native American” named varieties bred by the U.S. National Arboretum. These hybrids were specifically developed with disease resistance as a top breeding priority. If powdery mildew is your main frustration, switching to one of these hybrids may eliminate the problem entirely without any sprays.

Bark scale resistance is less well characterized because the pest is newer to the United States and large-scale cultivar screening is still ongoing. Anecdotally, some cultivars seem to attract heavier infestations than others, but formal resistance ratings comparable to the powdery mildew data are not yet established. For now, the best defense against bark scale is the cultural and chemical toolkit described above, combined with good tree health.

When the White Spots Are Something Else Entirely

Not every white mark on a crepe myrtle is powdery mildew or bark scale. A few other possibilities occasionally confuse gardeners:

Lichen: Flat, crusty patches of white, green, or gray on the bark. Lichen is not a disease or a pest. It is a harmless organism that grows on surfaces exposed to light and moisture. It does not damage the tree and does not need treatment. Lichen is more visible on crepe myrtle than on most trees because crepe myrtles naturally shed their outer bark, revealing smooth surfaces where lichen shows up prominently.
Woolly aphids: Small clusters of white, cottony material on stems or leaf undersides. These are aphids covered in waxy filaments. They produce honeydew like bark scale, so sooty mold can follow. A strong blast of water or an insecticidal soap spray usually clears them out.
Sunscald or paint residue: Occasionally, white patches on the trunk are simply areas where old bark has peeled to reveal the lighter wood underneath, which is normal. Crepe myrtles are famous for their exfoliating bark, and the freshly exposed inner bark can be strikingly pale.

If the white material rubs off as a powder and is concentrated on leaves and new growth, it is almost certainly powdery mildew. If it is stuck to the bark and leaves a pink or lavender smear when crushed, it is bark scale. If it is flat, firmly attached, and does not smear, it is likely lichen and harmless. Getting the identification right saves you from spraying fungicide on an insect problem or insecticide on a fungal one.

Seasonal Timing for Prevention and Treatment

Timing your interventions with the seasons makes them more effective and reduces wasted effort. Here is a rough calendar for managing both powdery mildew and bark scale:

In late winter, before new growth begins, prune your crepe myrtle to open up the canopy. This is also a good time to scrub bark scale off the trunk if you noticed an infestation the previous year. Removing dead or crossing branches improves air circulation for the growing season ahead.

In early spring, apply a slow-release fertilizer and, if bark scale is a concern, consider a soil drench with a systemic insecticide. Doing this before bloom protects pollinators while still giving the product time to move through the tree before crawler activity peaks.

In late spring and early summer, watch for bark scale crawlers and powdery mildew. Crawlers are active when temperatures warm up consistently, and powdery mildew tends to appear when warm, humid days are followed by cooler nights. This is the window when contact sprays for crawlers and preventive fungicide applications for mildew are most effective.

Through summer and into fall, monitor and retreat as needed. Powdery mildew pressure usually drops in the hottest weeks of summer (the fungus prefers moderate warmth, not extreme heat) but can return in early fall as nights cool down again. Bark scale may go through multiple generations during the growing season, so continued scouting helps you catch new buildups before they become severe.

By following this seasonal rhythm and combining good cultural practices with targeted treatments, most gardeners can keep their crepe myrtles free of white spots or at least reduce infestations to a level that does not affect the tree’s appearance and bloom.