Crepe Myrtle Leaves Turning Yellow: Understanding

Understanding Why Crepe Myrtle Leaves Turning Yellow

Crepe myrtles are one of the most popular ornamental small trees and shrubs grown for their summer blooms and exfoliating bark. When gardeners and homeowners discover their crepe myrtle leaves turning yellow, quite often they wonder if the treasured plant is now doomed. This blog will help in understanding yellow crepe myrtle leaves by outlining the causes of this phenomenon while addressing common diseases and pests, environmental conditions, and care advice to turn yellow crepe myrtle leaves back green.

Crepe Myrtle Leaves Turning Yellow
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Introduction to Crepe Myrtles

The crepe myrtles (Lagerstroemia species) boast a showy display of flowers throughout summer, in shades of pink, red, purple, or white. Originally native from Asia, not only widely cultivated for their nectar-rich flowers in warm areas of the Old World, but also introduced to tropical and temperate regions worldwide, for their peeling, multi-coloured bark and shapely, autumn foliage, including hues of purple.

Learning the Right Language Despite some crepe myrtles’ inherent ability to withstand drought and heat, and their required timely pruning due to twiggy growth at the plant’s trunk, all types are sensitive to environmental imbalances. This can be manifested in yellowing leaves, as an initial signal that the plant is under stress.

Understanding Leaf Yellowing

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Normal Seasonal Changes

First, a reality check: some leaf yellowing is normal. In late summer and fall, crepe myrtle leaves will show signs of turning yellow, red, and orange as they do every year. It’s no cause for worry; plants go through cycles, and this is one of them.

Abnormal Yellowing

Yellowing leaves outside the typical seasonal changes can indicate underlying issues. This abnormal yellowing, chlorosis, occurs when leaves lose their green pigment (chlorophyll). Understanding the causes of chlorosis is crucial for diagnosing and treating the problem effectively.

13 Stunning Types of Crape Myrtle to Grow

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Scientific NameGrowing ZonesFlowering SeasonLight RequirementsMature Height
Lagerstroemia indica ‘Fuchsia d’Été’ ® INDYFUS7–9Late spring through midsummerFull sun10–15 feet
Lagerstroemia indica ‘Whit VIII’6b–9Midsummer to early fallFull sun to partial shade10–12 feet
Lagerstroemia indica ‘Whit II’6–10SummerFull sun15–20 feet
Lagerstroemia indica ‘Whit X’7–10SummerFull sun8–10 feet
Lagerstroemia x ‘Natchez’7–10SummerFull sun20–30 feet
Lagerstroemia indica ‘Red Rocket’6–9Summer and early fallFull sun20–30 feet
Lagerstroemia indica ‘Pink Velour’7–10Summer and early fallFull sun10–12 feet
Lagerstroemia indica ‘Purple Magic’7–9Early summer, possible second flowering in early fallFull sun6–10 feet
Lagerstroemia indica ‘Plum Magic’7–9SummerFull sun12–14 feet
Lagerstroemia speciosa10b–11bSummerFull sun40–50 feet
Lagerstroemia indica ‘Tuscarora’7–9SummerFull sun10–20 feet
Lagerstroemia hybrid ’18LI’6–9Summer through fallFull sun10–12 feet
Lagerstroemia indica ‘Pocomoke’6–9SummerFull sun2–5 feet

Common Causes of Yellowing Leaves

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Watering Issues

Water stress is a common cause of leaf yellowing in crepe myrtles. Both overwatering and underwatering can lead to chlorosis. Overwatering can suffocate roots, causing them to rot and impairing their ability to uptake nutrients. Underwatering, on the other hand, leads to dehydration and nutrient deficiencies.

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Soil Conditions

Crepe myrtles prefer well-draining soil. Heavy clay soils that retain water can cause root rot and other issues, while sandy soils may drain too quickly, leaving the plant thirsty. Soil pH also plays a role; crepe myrtles thrive in slightly acidic to neutral soils (pH 5.5 to 7.0). Alkaline soils can inhibit nutrient uptake, particularly iron.

Climate and Weather

Extreme weather conditions, such as prolonged drought or excessive rainfall, can stress crepe myrtles. Additionally, sudden temperature fluctuations may cause temporary yellowing as the plant adjusts.

Nitrogen Deficiency

Nitrogen is essential for chlorophyll production. A lack of nitrogen can cause older leaves to turn yellow and drop prematurely. This deficiency often presents as uniform yellowing across the plant.

Iron Chlorosis

Iron chlorosis is common in alkaline soils, where iron becomes unavailable to plants. This deficiency typically affects new growth first, causing yellow leaves with green veins.

Aphids

Aphids are small, sap-sucking insects that can cause significant damage to crepe myrtles. They excrete honeydew, a sticky substance that promotes the growth of sooty mold, further stressing the plant and leading to yellowing leaves.

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Powdery Mildew

Powdery mildew is a fungal disease that affects crepe myrtles, especially in humid conditions. It presents as a white, powdery coating on leaves and can cause them to turn yellow and drop prematurely.

Cercospora Leaf Spot

Cercospora leaf spot is another fungal disease that affects crepe myrtles. It causes small, dark spots on the leaves, which eventually turn yellow and fall off. This disease is more prevalent in late summer and fall.

Scale

Scale insects feed on the sap in the leaves, twigs, and branches of the crepe myrtle. They extract nutrients from these parts and deposit their excrement on the leaves, causing them to turn yellow. These insects appear as small bumps on the surface of the leaves or stems.

Mites

 Mites are tiny arachnids that live on the underside of leaves, sucking plant juices. They can range in color from white to red, blue, and black. Mite infestations typically cause damage during hot summers when plants are stressed due to lack of water and nutrients. To control mites on crepe myrtles, spray the foliage with insecticidal soap or neem oil every two weeks during the summer months.

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Mealybugs

 Mealybugs are small insects that suck sap from plants and secrete a waxy substance called honeydew, which promotes the growth of sooty mold. They often attack new growth initially, then move upward along the stems, congregating under protective flaps of bark or in leaf axils (where new buds emerge). Damage includes wilting, deformed leaves, and dying branches.

To manage mealybugs, apply dormant horticultural oil in early spring before new growth emerges, or treat weekly with insecticidal soap if they are detected in winter or early spring.

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Whiteflies 

Whiteflies are tiny flying insects that resemble small moths. Adult whiteflies have four clear wings, while their larvae resemble maggots with clear bodies and blackheads. Two types of whiteflies commonly affect plants: the sweetpotato wireworm (Bemisia tabaci), which feeds on the roots of grasses and weeds, and the silverleaf whitefly (Bemisia argentifolii), which feeds on the foliage of trees, shrubs, and vines, including crepe myrtles. Silverleaf whiteflies can cause significant damage to both fruit trees and ornamental plants.

Age

This issue is common with this type of tree, especially if it is over 15 years old. The leaves begin to turn yellow and eventually fall off.

The cause is an imbalance in the tree’s nutrient intake. Excess nitrogen leads to overproduction of chlorophyll, resulting in yellowing and leaf drop. Conversely, a nitrogen deficiency in the soil will make the tree’s branches weak and reduce the number of healthy green leaves.

To remedy this, remove all dead branches and provide appropriate care by adding nitrogen-rich fertilizer to the soil.

Soil health

The leaves of your Crepe Myrtle may turn yellow due to a lack of essential nutrients such as nitrogen (N) and potassium (K). To address this issue, apply fertilizer at half strength while watering your tree or shrub. The optimal type of fertilizer depends on your soil type: sandy loam soils require more nitrogen, whereas clay soils need more potassium.

The soil’s pH level affects the availability of nutrients for plant growth. A pH level that is too high or too low can hinder nutrient absorption. Soil with a pH below seven is acidic, while soil with a pH above seven is alkaline. You can test your soil’s pH using a kit from your local hardware store or nursery. If you observe that your Crepe Myrtle leaves are turning yellow, especially if the entire leaf is affected, it may indicate a need to adjust the soil’s pH by adding lime or sulphur.

Overfertilization

Over-fertilization can cause the leaves of the Crepe Myrtle to turn yellow or brown. This occurs when the plant cannot absorb all the added nutrients, often due to applying too much fertiliser at once. Excess fertiliser builds up in the soil, blocking access to other essential nutrients like nitrogen and potassium. To prevent over-fertilization, use slow-release fertilisers instead of liquid ones. These fertilisers gradually release nutrients over time, reducing the risk of overfeeding your plants.

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Soil Drainage 

Poor soil drainage can lead to root rot and root death, resulting in yellowing leaves. Compacted soil or insufficient air pockets within the soil profile causes poor drainage. To improve soil drainage, amend your soil with organic matter such as composted manure or aged sawdust before planting. This will provide plenty of moisture-retaining organic matter to help keep the soil moist during dry periods without becoming waterlogged during rainy seasons.

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Treatment and Prevention

Proper Watering Techniques

Maintaining consistent soil moisture is crucial. Water deeply and less frequently to encourage deep root growth. Mulching around the base of the plant can help retain soil moisture and regulate temperature.

Soil Amendments

Improving soil structure with organic matter, such as compost, can enhance drainage in clay soils and moisture retention in sandy soils. Adjusting soil pH with sulfur or lime can also help make nutrients more available to the plant.

Fertilization Strategies

Regular fertilization can address nutrient deficiencies. A balanced, slow-release fertilizer applied in early spring can provide necessary nutrients throughout the growing season. For specific deficiencies, targeted supplements like iron chelates may be used.

Pest and Disease Control

For aphids, horticultural oils or insecticidal soaps can be effective. Introducing beneficial insects, such as ladybugs, can also help control aphid populations. Fungal diseases can be managed by improving air circulation around the plant, avoiding overhead watering, and applying fungicides when necessary.

Long-term Care Tips

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Pruning Practices

Pruning crepe myrtles in late winter encourages healthy growth and improves air circulation, reducing the risk of diseases. Remove any dead or diseased wood and thin out crowded branches.

Seasonal Maintenance

Regularly inspect your crepe myrtles for signs of stress or disease. Keep the area around the plant free of fallen leaves and debris, which can harbor pests and diseases.

Integrated Pest Management

Implementing integrated pest management (IPM) strategies can help maintain a healthy balance in your garden. This approach includes monitoring pest levels, using biological controls, and applying chemical treatments only when necessary.

How to Revive a Stressed Crepe Myrtle

Steps to Revive

  1. Identify the Problem: Diagnose the cause of stress or yellowing.
  2. Take Corrective Action: Apply the appropriate solutions based on the identified problem.
  3. Provide TLC: Ensure consistent care, including proper watering, fertilization, and pest control.

Long-Term Care

Maintain regular care routines to prevent future stress and ensure the long-term health of your crepe myrtle.

FAQs

Why are my crepe myrtle leaves turning yellow and falling off?

Yellowing leaves that fall off may indicate overwatering, nutrient deficiencies, or pest infestations. Inspect the plant closely to determine the cause and take appropriate action.

How often should I water my crepe myrtle?

Water newly planted crepe myrtles regularly to establish roots, then reduce frequency. Mature trees typically need water only during dry periods.

Can yellow leaves turn green again?

If yellowing is caught early and the underlying issue is resolved, new growth will be healthy and green. However, severely damaged leaves may not recover.

What is the best fertilizer for crepe myrtles?

Use a balanced, slow-release fertilizer formulated for flowering trees and shrubs. Follow label instructions for application rates and timing.

How can I prevent fungal infections on my crepe myrtle?

Ensure good air circulation, avoid overhead watering, and apply fungicides as needed. Pruning to maintain an open canopy can also help.

Are crepe myrtles susceptible to any specific pests?

Yes, common pests include aphids, spider mites, and whiteflies. Regular monitoring and prompt treatment can prevent serious infestations.

Conclusion

Yellowing leaves on crepe myrtles can be alarming, but understanding the causes and implementing proper care practices can mitigate the issue. By paying attention to environmental factors, nutrient levels, and potential pests and diseases, gardeners can ensure their crepe myrtles remain vibrant and healthy. Regular maintenance, including proper watering, soil management, and pest control, will help prevent yellowing leaves and keep your crepe myrtles flourishing for years to come.