The crape myrtle, Lagerstroemia indica, is a popular ornamental tree known for its vibrant, long-lasting summer flowers and resilient nature. When the leaves begin to curl, cup, or distort, it signals that the plant is experiencing underlying stress or damage. This change in foliage shape is a protective or symptomatic response, requiring a careful diagnosis of environmental conditions, pests, or external agents. Understanding the specific presentation of the curling is the first step toward restoring the tree’s health.
Curling Caused by Sap-Sucking Pests
Two primary groups of sap-sucking pests are often responsible for leaf curling symptoms on crape myrtles. The crape myrtle aphid feeds specifically on the underside of new, tender leaves and shoots, which causes the foliage to curl inward and become distorted as it grows. The constant removal of sap from the plant’s vascular tissue weakens the new growth, resulting in the characteristic puckering and malformation.
Aphid feeding also produces a sticky, sugary liquid waste known as honeydew, which coats the leaves and branches. This honeydew then supports the growth of sooty mold, a black fungus that can cover the leaf surface, hindering photosynthesis. A fine, black coating on the leaves and nearby surfaces is a strong indicator of an aphid or scale infestation, even if the tiny insects themselves are not immediately visible.
Spider mites, which are technically arachnids, are another pest that causes leaves to curl. These microscopic pests thrive in hot, dry conditions and use needle-like mouthparts to pierce individual plant cells and extract their contents. This cellular damage initially creates a stippled or bronzed appearance on the leaves. The leaves may then curl upward or inward as a reaction to the injury and moisture loss. The presence of fine, silky webbing, particularly on the undersides of the leaves, is the most diagnostic clue for a spider mite problem.
Environmental and Cultural Stressors
Leaf curling often results from improper cultural practices, particularly those related to water availability. During periods of drought or intense heat, a crape myrtle’s leaves will curl inward, or “cup,” as a survival mechanism. This physiological response reduces the leaf’s exposed surface area, which minimizes water loss through transpiration and conserves moisture.
Conversely, an over-watered tree or one planted in poorly drained soil can exhibit similar drought-like symptoms, including leaf curling. When the soil is perpetually waterlogged, the roots are deprived of oxygen, which impairs their function and can lead to root rot. The damaged roots are unable to efficiently absorb water and nutrients, effectively mimicking a severe drought and causing the leaves to curl from water stress.
Other environmental issues, such as transplant shock or incorrect planting depth, can also induce general plant stress that manifests as curled foliage. A newly planted tree may curl its leaves as it struggles to establish a functional root system. Rapid fluctuations in temperature or extended periods of intense sunlight can also contribute to temporary leaf cupping as the plant attempts to regulate its internal temperature and moisture balance.
Accidental Chemical Damage
One cause of leaf curling is accidental exposure to certain herbicides, particularly growth-regulator types like 2,4-D or Dicamba. These chemicals are designed to kill broadleaf weeds by mimicking plant hormones. Even a small amount of overspray or vapor drift can cause severe distortion in desirable plants like crape myrtles. Symptoms are often specific, including severe cupping, twisting, and elongation of the leaves and stems.
Herbicide damage typically affects the newest growth rapidly, sometimes appearing only a few days after application. The direction of the curl can sometimes distinguish the chemical; 2,4-D often causes downward curling, while Dicamba may result in leaves that curl upward. Chemical damage is suggested if multiple, unrelated plants in the landscape show similar symptoms simultaneously.
Other chemical issues, such as misapplied fertilizers or pesticides, can cause a chemical burn that leads to leaf distortion. However, the systemic, contorted growth resulting from herbicide drift is distinctive.
Actionable Steps for Diagnosis and Recovery
The recovery process begins with a systematic inspection to pinpoint the cause of the leaf curling. Start by examining the newest leaves for signs of pests, specifically checking the undersides for tiny insects, sticky honeydew, or fine webbing. If pests are present, a strong jet of water can dislodge aphids and mites from the foliage, and this can be repeated every few days. For more severe infestations, an application of insecticidal soap or horticultural oil, which smothers the pests, can be effective.
Next, assess the soil moisture by inserting a finger several inches deep into the soil around the base of the tree. If the soil is dry, implement a deep, slow watering schedule to ensure the root zone is saturated, encouraging the leaves to flatten out as hydration improves. If the soil is soggy, water less frequently, and consider improving the drainage to prevent root stress.
If the curling is severe and accompanied by twisting and distortion on multiple plants, chemical drift is the likely culprit. For accidental herbicide exposure, little can be done immediately other than ensuring the tree is well-hydrated and protected from further stress. Flush the soil with water to dilute any chemical that may have reached the roots, and prune off the most severely damaged foliage.
Crape myrtles are generally resilient. With time and good ongoing care, they will typically grow out of herbicide damage by producing new, healthy leaves.