Crape myrtles are popular ornamental trees and shrubs. Despite their resilience, yellowing leaves often signal underlying issues. Understanding the reasons for this discoloration is important for maintaining the plant’s health.
Natural Yellowing
Not all yellowing leaves on a crape myrtle indicate a problem. Like many deciduous plants, crape myrtles naturally transition to yellow, orange, or red in late summer and fall before dropping. This is a normal part of their life cycle as they prepare for dormancy.
Older leaves in the interior or lower parts may also yellow and fall as the plant produces new growth. This natural shedding allows the plant to focus energy on new development. When yellowing occurs as part of these natural cycles, no intervention is needed.
Environmental Factors and Nutrient Issues
Environmental conditions and nutrient availability frequently cause yellowing leaves in crape myrtles. These factors induce stress, impacting the plant’s ability to produce chlorophyll.
Watering Problems
Both too much and too little water can lead to yellowing leaves. Overwatering suffocates roots, causing rot and impairing nutrient absorption. This results in yellowing leaves. Conversely, underwatering or drought stress causes dehydration, leading to nutrient deficiencies and crispy, yellow leaves. Check soil moisture before watering, ensuring the top few inches are dry. Provide well-draining soil to prevent waterlogging.
Nutrient Deficiencies
Inadequate soil nutrients, particularly nitrogen and iron, commonly cause yellowing leaves. Nitrogen deficiency results in uniform yellowing of older leaves. Iron chlorosis, often seen in alkaline soils where iron is less available, presents as yellow leaves with green veins, affecting newer growth first. Address these deficiencies by applying a balanced fertilizer or, for iron chlorosis, amending soil to lower pH or using chelated iron supplements.
Light Exposure
Crape myrtles thrive in full sun, requiring at least six hours of direct sunlight daily. Insufficient light leads to pale, yellowing leaves and sparse foliage as the plant struggles to photosynthesize. Planting crape myrtles in sunny locations ensures vigorous growth and healthy leaf color.
Temperature Stress
Extreme temperatures can cause crape myrtle leaves to yellow and drop. Sudden cold snaps or prolonged heat stress shock the plant, leading to discoloration. Providing adequate water during hot periods and protection during unexpected freezes can mitigate temperature-induced yellowing.
Pest Infestations
Several common pests cause crape myrtle leaves to yellow by feeding on plant sap.
Crape myrtle aphids are pale yellowish-green insects that feed on the underside of leaves, sucking sap. Their feeding causes yellow spots, overall yellowing, leaf distortion, and premature drop. Aphids also excrete honeydew, leading to black sooty mold. Dislodge aphids with a strong stream of water, or apply insecticidal soaps or horticultural oils for severe infestations.
Scale insects also feed on plant sap, appearing as small bumps on stems and leaves. Their feeding yellows leaves and produces honeydew, leading to sooty mold. Spider mites, tiny arachnids thriving in hot, dry conditions, feed on leaves, causing small yellow or white spots (stippling). Severe infestations can turn leaves entirely yellow or red, potentially killing them. Manage these pests by hosing down the plant, using insecticidal soaps, or horticultural oils.
Disease Concerns
Fungal and bacterial diseases can also cause yellowing leaves on crape myrtles.
Cercospora leaf spot, caused by the fungus Cercospora lythracearum, leads to yellow or brown spots on leaves. These spots can cause leaves to turn entirely yellow, orange, or red, leading to premature defoliation, especially in late summer and fall. While not lethal, repeated severe infections reduce vigor. Manage this disease by selecting resistant varieties, ensuring good air circulation, and cleaning up fallen leaves to reduce fungal spores.
Powdery mildew, caused by the fungus Erysiphe lagerstroemiae, appears as a white to grayish powdery growth on leaves, new shoots, and flower buds. Severe infections can cause leaves to turn yellowish or brown, become distorted, and drop prematurely. This disease thrives in shady, damp conditions with poor air circulation. Prevent by planting in full sun, ensuring adequate air circulation, and choosing mildew-resistant crape myrtle varieties. Horticultural oils or neem oil can treat it.
Long-Term Health and Prevention
Maintaining crape myrtle health involves proper planting and consistent care. Select a suitable planting site with full sun and well-draining soil. Adequate space between plants improves air circulation, deterring fungal diseases.
Water regularly during dry periods, avoiding overwatering to protect root health. Fertilize based on soil test results to ensure the plant receives necessary nutrients. Routine inspection for early signs of pests or diseases allows for prompt intervention. Pruning for good air flow and removing infected branches contributes to overall plant resilience.