Quick Guide: Crape Myrtle Diseases & Insect Pests
Affected Plants: Crape myrtle (Lagerstroemia indica and hybrids)
Primary Disease Types: Powdery mildew; Cercospora leaf spot; sooty mold
Primary Insect Pests: Crape myrtle aphids; Japanese beetles; crape myrtle bark scale
Primary Causes: Fungal pathogens; sap-sucking insects; defoliating beetles
Most Important Prevention Strategy: Plant resistant varieties and provide full sun with good air circulation
Chemical Control: Fungicides (myclobutanil, propiconazole, thiophanate-methyl, copper); insecticides (imidacloprid, horticultural oil, insecticidal soap, pyrethrins, neem oil, permethrin, cyfluthrin, cyhalothrin, acephate, malathion)
Crape myrtles (Lagerstroemia indica) are essentially trouble-free small trees. The most common problems include powdery mildew, Cercospora leaf spot, aphids, Japanese beetles, and sooty mold.
Related HGIC Resources:
HGIC 1008, Crape Myrtle
HGIC 1009, Crape Myrtle Pruning
Powdery mildew typically coats the flower buds (above) and foliage of crape myrtle.
James Blake, ©2007 HGIC, Clemson Extension
Crape Myrtle Diseases: Powdery Mildew on Crape Myrtle
Powdery mildew is one of the most common fungal diseases affecting crape myrtle, particularly in shaded or humid conditions.
Cause of Powdery Mildew on Crape Myrtle
Powdery mildew is one of the most common problems of crape myrtle, and it is caused by the fungus Erysiphe lagerstroemiae. The disease is most serious in shady, damp locations, especially where plants are crowded, and air circulation is poor. Fungal development is favored by high humidity at night and dry, mild daytime conditions, as often occur during spring and fall.
Signs and Symptoms of Powdery Mildew on Crape Myrtle
- Patches of white to grayish powdery growth
- Occurs on the surfaces of leaves, flowers, and new shoots
- Heavily infected flowers may fail to open
- Infected parts of the plant become distorted and stunted
Prevention & Treatment for Powdery Mildew on Crape Myrtle
Cultural Controls
- Locate plants in full sun
- Remove sprouts from the base of the plant
- Plant resistant varieties
- Avoid susceptible varieties of crape myrtle
- Remove diseased twigs and branches if only a few shoots are infected
- Remove sprouts (suckers) at the plant base; they are susceptible to powdery mildew
- Once sprouts become infected, the fungus spreads easily to the upper plant portions
Resistant Crape Myrtle Varieties
The extent of resistance to powdery mildew in a particular variety may vary from location to location and depend on environmental conditions.
The Lagerstroemia indica x fauriei hybrids developed at the U.S. National Arboretum in Washington, D.C., are resistant to powdery mildew.
Varieties with very good resistance to powdery mildew and fairly good tolerance to Cercospora leaf spot include:
- ‘Apalachee’
- ‘Basham’s Party Pink’
- ‘Caddo’
- ‘Dodd #2’
- ‘Fantasy’
- ‘Glendora White’
- ‘Hopi’
- ‘Lipan’
- ‘Miami’
- ‘Osage’
- ‘Pecos’
- ‘Regal Red’
- ‘Sarah’s Favorite’
- ‘Sioux’
- ‘Tonto’
- ‘Tuscarora’
- ‘Tuskegee’
- ‘Velma’s Royal Delight’
- ‘Wichita’
‘Apalachee’ and ‘Fantasy’ are totally resistant to powdery mildew.
Varieties with some resistance:
- ‘Catawba’
- ‘Cherokee’
- ‘Seminole’
- ‘Yuma’
Varieties to Avoid for Powdery Mildew Susceptibility:
- ‘Gray’s Red’
- ‘Orbin’s Adkins’
- ‘Carolina Beauty’
- ‘Wonderful White’
- ‘Raspberry Sundae’
- ‘Potomac’
Chemical Control for Powdery Mildew on Crape Myrtle
If the disease is severe enough to warrant chemical control, select a fungicide containing one of the following:
- Myclobutanil
- Propiconazole
- Thiophanate-methyl
- Copper-based fungicides
Multiple applications may be required. Apply all chemicals according to the directions indicated on the label.
See Table 1 for specific products.
For more information about powdery mildew, visit HGIC 2049, Powdery Mildew on Landscape and Garden Plants.
Crape Myrtle Diseases: Cercospora Leaf Spot on Crape Myrtle
Cercospora leaf spot is a warm-season fungal disease that can cause significant late-summer defoliation of susceptible crape myrtle cultivars.
Cause of Cercospora Leaf Spot on Crape Myrtle
Leaf spots caused by Cercospora lythracearum may appear on crape myrtles and are caused by the fungus Cercospora species. This disease typically occurs during periods of warm, moist weather.
Symptoms of Cercospora Leaf Spot on Crape Myrtle
- Yellow spots (⅛ to ¼ inch diameter) appear on the upper leaf surface.
- White-grey sporulation of the fungus on the lower leaf surface.
- Can result in almost complete defoliation of the plant in late summer and fall in susceptible cultivars.
Prevention & Treatment for Cercospora Leaf Spot on Crape Myrtle
Cultural Controls
- Select resistant varieties for new plantings.
- Provide good air circulation.
- Avoid overcrowding plants.
Resistant Crape Myrtle Varieties for Cercospora Leaf Spot
The varieties that have exhibited resistance in field trials include:
- ‘Fantasy’
- ‘Tonto’
- ‘Tuscarora’
- ‘Tuskegee’
- ‘Velma’s Royal Delight’
The amount of resistance may vary from location to location and may depend on particular environmental conditions.
Chemical Control for Cercospora Leaf Spot on Crape Myrtle
If the disease is severe enough to warrant using chemicals for control, the following fungicides will control Cercospora leaf spot:
- Thiophanate-methyl
- Myclobutanil
(These are the same fungicides used for powdery mildew; see Table 1 for specific products.)
Apply all chemicals according to directions on the label.
Crape Myrtle Insect Pests: Crape Myrtle Aphids on Crape Myrtle
Crape myrtle aphids are the most common insect pest of crape myrtle in South Carolina and are responsible for honeydew and sooty mold development.
Cause & Biology of Crape Myrtle Aphids on Crape Myrtle
The most common crape myrtle insect pest in South Carolina is the crape myrtle aphid (Sarucallis kahawaluokalani). They are found on the leaves and twigs and only on crape myrtle trees.
Crape myrtle aphids are pale yellowish-green with black spots on the abdomen and vary in length from 1/16 to ⅛ inch long.
They overwinter (survive the winter) as eggs, which hatch in the spring. During the growing season, females give birth to live young. Since it takes about 10 days to reach maturity, several generations are produced each growing season. At the end of the growing season, females produce eggs that overwinter.
A heavy infestation of aphids on the underside of a leaf.
Image from John Herbert, University of Florida
Symptoms & Damage from Crape Myrtle Aphids
- Aphids insert their mouthparts into tender new leaves and suck plant sap.
- Aphids excrete large amounts of sugary liquid called honeydew.
- Honeydew can completely coat leaves when populations are high.
- Yellow spots develop on leaves due to injected saliva.
- Feeding on young leaves often causes leaf distortion.
- Buds, branch tips, and flowers can also be affected.
Honeydew serves as food for sooty mold fungi (Capnodium species) and attracts ants, wasps, and flies.
Prevention & Control of Crape Myrtle Aphids
Resistant Crape Myrtle Hybrids
The following Lagerstroemia indica x fauriei hybrids have moderate resistance to aphids:
- ‘Muskogee’
- ‘Natchez’
- ‘Tuscarora’
- ‘Acoma’
- ‘Tuskegee’
- ‘Hopi’
- ‘Pecos’
- ‘Zuni’
- ‘Biloxi’
- ‘Miami’
- ‘Wichita’
- ‘Apalache’
- ‘Comanche’
- ‘Lipan’
- ‘Osage’
- ‘Sioux’
- ‘Yuma’
- ‘Caddo’
- ‘Tonto’
- ‘Choctaw’
- ‘Fantasy’
Consider using these in new plantings.
Biological Control of Crape Myrtle Aphids
Several predators feed on the crape myrtle aphid, including:
- Ladybird beetles (ladybugs) and their larvae (immature forms)
- Green lacewings and their larvae
- Hover fly maggots
- Parasitic wasps
- Entomophagous (insect feeding) fungi
To the extent possible, these natural predators should be allowed to reduce aphid populations.
Many aphids can also be removed by spraying plants with a strong stream of water. Spraying may need to be repeated regularly, as needed.
Chemical Control of Crape Myrtle Aphids
Aphids are very difficult to control with insecticides because of their rapid reproduction. Using insecticides may also kill beneficial predators.
If necessary, insecticides labeled for homeowners include:
- Insecticidal soap
- Horticultural oil
- Pyrethrins
- Neem oil
- Permethrin
- Cyfluthrin
- Cyhalothrin
- Acephate
- Malathion
Soil drenches of imidacloprid in the spring will control aphids and last longer within the plant to prevent future infestations by aphids and other insect pests (see Table 1 for specific products).
As with all pesticides, read and follow all label instructions and precautions.
For more information about aphids, visit HGIC 2009, Integrated Pest Management (I.P.M.) for Aphids.
Crape Myrtle Insect Pests: Japanese Beetles on Crape Myrtle
Japanese beetles feed on crape myrtle flowers and foliage during summer, causing noticeable cosmetic damage.
Biology of Japanese Beetles on Crape Myrtle
Adult Japanese beetles are about ½ inch in length and coppery-brown in color with metallic green heads.
They emerge from the soil and feed from May to August. They lay their eggs in the soil. Grubs hatch from the eggs and feed on grass roots. As the weather cools, grubs move deeper into the soil to overwinter.
In addition to crape myrtle, it will feed on nearly three hundred different plant species.
Symptoms & Damage from Japanese Beetles on Crape Myrtle
Adult Beetles Damage
- Eat flowers
- Skeletonize leaves (eat leaf tissue between the veins, resulting in a lacy skeleton remaining)
Grub Damage
- Feed on the roots of plants
- Especially on the roots of grasses
Both adult beetles and their larvae (grubs) can seriously damage plants as a result of their feeding.
Prevention & Control of Japanese Beetles on Crape Myrtle
Multiple approaches are necessary for controlling Japanese beetles.
Mechanical Control
- Handpick adults and drown them in a pail of soapy water
- Japanese beetle traps are available commercially or can be homemade
Keep traps at least 50 feet from the crape myrtle tree, or you may create more of a problem by attracting them to the area.
Biological Control
Milky spore, Paenibacillus popilliae, is a disease-causing bacterium that is effective against Japanese beetle grubs that live in the soil and feed on turfgrass roots, but not the adults. It is commercially available for homeowner use.
Chemical Control for Japanese Beetles on Crape Myrtle
Products labeled for use by homeowners include those containing:
- Neem oil
- Cyfluthrin
- Permethrin
- Cyhalothrin
- Acephate
Soil drenches of imidacloprid in the spring will significantly reduce Japanese beetle damage and last longer within the plant, helping prevent future infestations by additional pests (see Table 1 for specific products).
As with all pesticides, read and follow all label instructions and precautions.
For more information about Japanese beetles, visit Japanese Beetles.
Crape Myrtle Insect Pests: Crape Myrtle Bark Scale on Crape Myrtle
Crape myrtle bark scale is an emerging pest that can cause heavy infestations on stems and trunks.
Information on Crape Myrtle Bark Scale on Crape Myrtle
This crape myrtle pest is a more recent arrival.
For information on this insect pest and control measures, please see:
Other Crape Myrtle Problems: Sooty Mold on Crape Myrtle
Sooty mold develops on honeydew deposits left by sap-sucking insects and indicates an underlying insect problem.
Cause of Sooty Mold on Crape Myrtle
Sooty mold completely covers these crape myrtle leaves.
Image from John Herbert, University of Florida
Sooty mold is caused by fungi that grow on the sugary substance called honeydew, which is produced by various insects that suck sap from the plant.
Aphids, scales, mealybugs, and whiteflies most commonly cause this problem.
Sooty mold indicates an insect problem on the plant.
Symptoms of Sooty Mold on Crape Myrtle
- Leaf and stem surfaces are covered with a black sooty substance
- Leaves and stems appear black and dirty
- Mold may completely coat leaves when honeydew accumulation is heavy
Sooty molds are unsightly but relatively harmless, as they do not directly attack the plant.
Prevention & Treatment of Sooty Mold on Crape Myrtle
Control the Insect Source
- Reduce aphid numbers by allowing beneficial insects, such as lady beetles, to inhabit the plant
- Remove aphids with a strong spray of water
Controlling the insect problem can reduce excessive amounts of sooty mold.
Washing Sooty Mold from Leaves (Optional)
Although not necessary, sooty mold can be washed from the leaves by following these steps:
- Spray foliage with a dish soap solution (4 ounces per gallon of water)
- Wait three to four minutes
- Rinse the foliage with a strong stream of water
Other Crape Myrtle Problems: Lichens on Crape Myrtle
Lichens are harmless organisms that commonly grow on older or declining crape myrtle bark.
Cause of Lichens on Crape Myrtle
These harmless lichens are growing on an older crape myrtle.
Karen Russ, ©2007 HGIC, Clemson Extension
A lichen is an unusual organism composed of a fungus, a green alga, and/or a cyanobacterium living together in the same body.
Typically, they occur in abundance on plants that are declining in health or vigor. Less vigorous plants tend to be more open with less foliage, which increases sunlight penetration and subsequent lichen growth.
They are harmless to the plant and are in no way responsible for the poor health of the plant.
Symptoms of Lichens on Crape Myrtle
- Green to gray-green leafy growth on bark
- Crusty growths on the trunks or branches
- Often more visible on plants declining in health or vigor
Prevention & Treatment of Lichens on Crape Myrtle
Controls are not necessary.
Lichens will gradually disappear once the plant’s health is restored.
Consumer Products Labeled for Lichen Control
The following consumer products list control on their labels:
- Bonide Moss Max RTS
- Bayer BioAdvanced 2-in-1 Moss & Algae Killer & Cleaner RTS
- Scott’s MOSS-EX 3-in-1 RTS
All products say to apply only to the hardened bark of trees. They should be applied only to the bark, with no foliar contact.
These products are not labeled for use on shrubs.
All three are identical and contain 22.11% potassium salts of fatty acids.
RTS = Ready to Spray (hose-end sprayer bottle)
Insecticides & Fungicides for Crape Myrtle Insect Pest & Disease Control. (Table 1.)
The following active ingredients are labeled for homeowner use against crape myrtle diseases and insect pests.
Fungicides for Crape Myrtle Diseases
| Active Ingredient | Examples of Brand Names & Products |
| Copper-based Fungicides | Bonide Captain Jack’s Liquid Copper Fungicide Bonide Copper Fungicide Spray or Dust Ready to Use Camelot O Fungicide/ Bactericide Espoma Organic Copper Soap Ready-to-Use Fungicide Monterey Copper Fungicide Garden Spray Liqui-Cop Natural Guard by ferti-lome Copper Soap Fungicide Concentrate Natural Guard by ferti-lome Copper Soap Fungicide Ready to Use Southern Ag Liquid Copper Fungicide |
| Myclobutanil | Ferti-lome F-Stop Lawn & Garden Fungicide Monterey Fungi-Max Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate For Gardens |
| Propiconazole | Banner Maxx II Fungicide |
| Bonide Infuse Systemic Disease Control | |
| Bonide Infuse Systemic Disease Control Lawn & Landscape Ready to Spray | |
| Ferti-lome Liquid Systemic Fungicide II | |
| Quali-Pro Propiconazole 14.3 Fungicide | |
| Thiophanate-methyl | Southern Ag Thiomyl Systemic Fungicide |
| Note: Control of diseases and insects on large trees is usually not feasible because adequate pesticide coverage of the foliage cannot be achieved. RTS = Ready to Spray (a hose-end sprayer) |
|
Insecticides for Crape Myrtle Insect Pests
| Active Ingredient | Examples of Brand Names & Products |
| Acephate | BioAdvanced Science-Based Solutions 2-in-1 Systemic Rose & Flower Care Granules with 6-9-6 Fertilizer Bonide Systemic Insect Control II |
| Cyfluthrin | BioAdvanced Science-Based Solutions 24 Hour Lawn Insect Killer Ready-to-Spray |
| BioAdvanced Science-Based Solutions Complete Brand Insect Killer for Soil & Turf Ready-to-Spray I | |
| BioAdvanced Science-Based Solutions Insect Killer for Lawns Ready-to-Spray | |
| BioAdvanced Science-Based Solutions Rose & Flower Insect Killer Ready-to-Use | |
| Horticultural Oil | Bonide All Seasons Horticulture Spray Oil Ready-to-Use Bonide All Seasons Horticulture & Dormant Spray Oil Ready-to-Spray Ferti-lome Horticultural Oil Spray Monterey Horticultural Oil Concentrate Monterey Horticultural Oil RTU Safer Brand Horticultural & Dormant Spray Oil Concentrate Southern Ag Parafine Horticultural Oil Summit Year-Round Spray Oil |
| Imidacloprid | BioAdvanced Science-Based Solutions 12 Month Tree & Shrub Insect Control Concentrate Landscape Formula BioAdvanced Science-Based Solutions 12 Month Tree & Shrub Protect & Feed Concentrate 2-1-1 BioAdvanced Science-Based Solutions 12 Month Tree & Shrub Protect & Feed Ready to Use Granules 2-1-1|BioAdvanced Science-Based Solutions 12 Month Tree & Shrub Protect & Feed II Concentrate 2-1-1 BioAdvanced Science-Based Solutions 12 Month Tree & Shrub Protect & Feed II Ready to Use Granules 2-1-1|BioAdvanced Science-Based Solutions 2 in 1 Systemic Rose & Flower Care Ready-to-Use Granules II Bonide Annual Tree & Shrub Insect Control w/ Systemaxx Bonide Systemic Granules Insect Control Bonide Systemic Insect Spray w/ Systemaxx Ready to Spray| Ferti-lome Tree & Shrub Drench Hi-Yield Systemic Insect Granules| Hi-Yield Systemic Insect Spray Ready-to-Spray Martin’s Dominion Tree & Shrub Insecticide Concentrate Monterey Once A Year Insect Control II |
| Insecticidal Soap | Bonide Insecticidal Soap Multi-purpose Insect Control Ready to Use Espoma Organic Insect Soap Multi-Purpose Insect Killer Garden Safe Brand Insecticidal Soap Insect Killer Miracle-Gro Nature’s Care Insecticidal Soap Natria Insecticidal Soap Ready-to-Use Natural Guard by ferti-lome Insecticidal Soap Concentrate Safer Brand Insect Killing Soap Concentrate II Whitney Farms Insecticidal Soap 1 |
| Cyhalothrin, Lambda or Gamma | Bonide Eight Insect Control Garden & Home II Ready to Use |
| Cutter Backyard Bug Control Spray Concentrate | |
| Cyzmic CS Controlled Release Insecticide | |
| Martin’s Cyonara Lawn & Garden Insect Control | |
| Martin’s Cyonara Lawn & Garden Insect Control Ready-to-Spray | |
| Spectracide Triazicide Insect Killer for Lawns & Landscapes | |
| Malathion | Bonide Malathion 50% Insect Control Gordon’s Malathion 50% Spray Hi-Yield 55% Malathion Insect Spray Martin’s Malathion 57% Ortho Max Malathion Insect Spray Concentrate Southern Ag Malathion 50% EC Spectracide Malathion Insect Spray Concentrate Tiger Brand 50% Malathion |
| Milky Spore | St. Gabriel Organics Milky Spore Granular Grub Control |
| Neem Oil | Bonide Captain Jack’s Neem Oil Concentrate Bonide Captain Jack’s Neem Oil Ready to Use Bonide Rose Rx 3-in-1 Concentrate Bonide Rose Rx 3-in-1 Ready to Use Espoma Organic Neem Oil 3n1 Fungicide/Miticide/Insecticide Garden Safe Fungicide 3 Garden Safe Fungicide 3 Concentrate Garden Safe Neem Oil Extract Concentrate Monterey 70% Neem Oil Fungicide/Insecticide/Miticide Natria Neem Oil Concentrate Natria Neem Oil Ready-to-Use Natural Guard Brand by ferti-lome Neem Safer Brand Neem Oil Concentrate Fungicide/Miticide/Insecticide Safer Brand Neem Oil RTU Fungicide/Miticide/Insecticide Southern Ag Triple Action Neem Oil |
| Permethrin | Bonide Eight Insect Control Vegetable, Fruit, & Flower Concentrate |
| Bonide Eight Yard & Garden Ready to Spray | |
| Hi-Yield 38 Plus Turf, Termite & Ornamental Insect Control | |
| Hi-Yield Lawn Garden Pet & Farm Insect Control | |
| Southern Ag Permetrol Lawn & Garden Insecticide | |
| Tiger Brand Super 10 Brand | |
| Pyrethrin | Monterey Bug Buster–O PyGanic Crop Protection EC 1.4 II PyGanic Crop Protection EC 5.0 II |
| Note: Control of diseases and insects on large trees is usually not feasible because adequate pesticide coverage of the foliage cannot be achieved.|RTS = Ready to Spray (a hose-end sprayer) | |
