Azalea Discoloration: What to Do About It


Azalea discoloration is usually an early symptom of a bigger issue. How can you help rejuvenate your plant
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When the azaleas’ spectacular flower display is over in late spring, we can still enjoy the beauty of their foliage. These shrubs’ shiny green leaves practically glow in the dappled shade under trees, and they make a lovely backdrop for summer blooming perennials. Winter landscapes benefit from the texture and interest provided by evergreen varieties.

Discoloration of the leaves occurs when problems arise. Should you be concerned if the leaves of your azaleas turn red, brown, yellow, black, or even white? Sometimes. It depends on what is causing the discoloration.

Leaves can change color simply because it is autumn and the season has arrived. Cold winds, dry spells, and other unfavorable weather conditions can also impact the color of the leaves. Cultural practices are our actions to care for our plants, such as selecting a location, planting, watering, and fertilizing. These practices can result in leaf discoloration if the care we provide is not what the azaleas prefer. Leaf discoloration can also be caused by insect infestations and fungal diseases.

Continue reading to learn what those color changes mean, what you can do about them, and how to prevent them from happening again.

Leaves Turn Red

Fall Color

In the fall, many azaleas turn beautiful shades of red, burgundy, or purple. Others may be orange or yellow in color. This is their natural autumn hue.

This is nothing to worry about; simply enjoy! Azaleas’ autumn colors are just as lovely as their spring blooms.

If the color change occurs earlier in the season, it could indicate water stress. During periods of dry weather, make sure your azalea is well watered. Also, ensure that the soil is well-drained. These plants despise wet feet!

The leaves of an azalea plant turning red under the sun

Leaves Turn Black

Sooty Mold 

Sooty mold is a black, powdery substance that grows on leaves. It is caused by a variety of fungal diseases that grow on the sticky secretions (“honeydew”) of insect pests, the most common of which is the whitefly. These pests are often challenging to detect because they live on the undersides of the leaves, but if you shake a branch vigorously, they will rise up in a cloud.

Sooty mold is primarily a cosmetic issue. While it is unsightly, it rarely causes harm to the plant. A mild dish soap and water solution can be used to remove sooty mold.

If the insects that produce honeydew are not controlled, sooty mold may reappear. Beneficial insects, sticky traps, and systemic insecticides can all control whiteflies. Foliar sprays are ineffective because whiteflies simply fly away when you approach with your spray bottle. Foliar sprays can harm beneficial insects, many of which are predators that will help you control pests.

Azalea leaved covered with black moldy dusts

Leaves Turn White 

Azalea leaves turn white for a variety of reasons. Powdery mildew or galls, insects such as mealybugs, or damage caused by aphids, lace bugs, or spider mites are all possibilities.

Powdery Mildew 

Powdery mildew is a fungal disease that appears when the weather is warm during the day and cool at night. It starts as white spots and spreads to cover the entire leaf with a white powdery coating.

Powdery mildew, as unsightly as it is, rarely kills a plant. Fungicides are difficult to control for this disease because it requires applications before the disease manifests and several applications at specific intervals to keep it at bay. Powdery mildew can be prevented by using horticultural oils.

Powdery mildew, like most fungal diseases, thrives in the presence of moisture, so avoid overhead watering. Watering the root zone aids in keeping the foliage dry.

powdery mildew forming on leaves and flowers of an azalea

Leaf Galls

Leaf galls form as a result of a fungus. Galls begin as light green, waxy growths on the leaves that eventually turn white, brown, and fall off. This disease is common in the southeast United States, and while it is not a major issue, it must be addressed.
The fungus overwinters in the buds and galls that fell to the ground during the previous growing season. It is critical to remove these fallen galls. Rain and watering wash the gall spores back onto the shrub. The best way to control this problem is to pick gall-infested leaves by hand.

azalea plant formed leaf galls

Insect Pests

As in the case of mealybug, white spots could be the insects themselves. Some aphid species are also white. A white speckled or mottled appearance indicates spider mite, lace bug, or aphid feeding damage. Spider mites build very fine webbing in the nodes of leaves and are especially active in hot, dry weather.

An azalea plant infested with white insect pests

Increasing the biodiversity in your garden goes a long way toward preventing pest populations from congregating. Pollinators and predators are both examples of beneficial insects. If you must use an insecticide or miticide, use a systemic product. These substances are absorbed by the plant’s vascular system and poison the pest as it feeds. Check that the product is labeled for the pest and that the instructions are followed exactly.

The leaves of a rhododendron plant damaged by fungal disease

Leaves Turn Brown

There are numerous causes for azalea leaves to turn brown, so you’ll need to be a bit of a detective here. Natural fall color, insufficient water, excessive water, or poor drainage, all of which contribute to root rot, could be the causes. Other possible causes include nutrient deficiencies or fertilizer burn.

Your azalea may be afflicted with fungal diseases such as dieback disease, insect pests, or even wind burn or sunscald. As in the case of dieback, all of the leaves on a single branch may be completely brown, or the leaves may have brown tips, edges, or spots.

It is impossible to turn brown leaves back to green once they have turned brown. To prevent the problem from recurring, grow azaleas in the best conditions possible.

Azalea leaves with black and brown spots

Too Much or Not Enough Water

Azaleas require moist, well-draining soil to thrive. When the shrubs are water-stressed, the edges and tips of the leaves are the first to turn brown. Dig a few inches down to see how moist the soil is at the root zone. If the soil is extremely wet, this can cause root rot. Allow it to dry and only water when necessary. Water it if it is extremely dry. Azaleas tolerate dry soil better than very wet soil.

A 2 to 3-inch layer of organic mulch, such as pine straw, will aid in soil moisture regulation. Using inorganic mulches such as rocks can both dry out the soil and keep it too wet.

Nutrient Deficiencies

Most nutrient deficiencies result in pale leaves, but they can also be brown. Azaleas are not heavy feeders, and if grown in a soil rich in organic matter and mulched as described above, they will thrive without any fertilizer. A soil test, on the other hand, can tell you what nutrients you need to add if you suspect a nutrient deficiency.

leaves of a plant with dried and brown parts

Fertilizer Burn

When the tips of the leaves turn brown, this can be an indication of fertilizer burn. Nitrogen-rich fertilizers can cause azalea roots and foliage to burn. To avoid fertilizer burn, always conduct a soil test to ensure that an application is necessary. If you accidentally over-fertilized the soil, flush it with plenty of water to dilute it.

Dieback Disease

Dieback is a difficult-to-control fungal disease. An entire branch and all of its leaves will be brown and lifeless. Sometimes it affects more than one branch, and other times it consumes the entire shrub. When the bark on a stem is removed, you will notice a reddish-brown discoloration on the inner wood.
Dead branches can be removed. Make sure your cuts are well below the diseased areas and that you sanitize your clippers between cuts.
Prevention is the best solution. Plant resistant varieties and keep plants healthy and stress-free by planting in shady areas and deeply watering during dry spells. Plants that are strong and healthy are better able to withstand disease and insect infestations.

drying autumn leaves under the heat of the sun

Other Fungal Diseases

Foliage fungal diseases, such as cercospora and septoria, begin as small brown spots on the leaves. The lesions spread and eventually cover the entire leaf as they age. Chemical fungicides can sometimes stop the spread of fungal diseases, but they must be applied at the first sign of the disease and then reapplied at very specific intervals. Read and carefully follow the label instructions.

Leaves of a plant damaged by a fungal disease

Insect Pests

Leaf miners attack a wide range of plants, not just azaleas. They feed between the layers of leaves, leaving distinct trails. As the leaf tissue dies, the trails turn brown. Before the larvae enter the leaf, leaf miners must be controlled.

A closeup picture of a leaf damaged by insect pests

Wind Burn

Wind burn occurs when the evergreen azalea foliage is dried out by cold winter winds. The leaves will have turned brown and shriveled. Horticultural oil, for example, can be applied late in the fall to help keep moisture in the leaves. To protect them, you can also make burlap windbreaks or plant hardier shrubs upwind of your azaleas.

Sunscald

Sunscald, or sunburn, can occur if azaleas are planted in too sunny a location. Remember that they do best in dappled shade or on the east side of your home. If you need to relocate your azalea, it’s not very difficult:  they have a shallow root system.

beautiful autumn leaves of an azalea plant

Leaves Turn Yellow or Pale Green

The shrub’s natural fall color could be yellow leaves. Other possible causes include cholorisis, nutrient deficiencies, drinking too much or not enough water, and sunburn. 

Dogs are another possible cause of yellow azalea leaves. When damage is seen on the lower part of the shrub, it is possible that neighborhood dogs are using your shrubbery as a toilet.

Chlorosis

Chlorosis is caused by a deficiency in chlorophyll. The veins of the leaves may be deep green, but the leaf tissue is yellow or pale green. A high soil pH is the most common cause of chlorosis in azaleas. Azaleas require soil pH levels ranging from 4.5 to 6.

Check the pH of your soil. To make the soil more acidic if it is too alkaline, use ferrous sulfate rather than aluminum sulfate; aluminum is toxic to azaleas. The pH of a soil, on the other hand, will not remain altered indefinitely; it will eventually return to its original state. Adding a lot of organic matter in the form of mulches like pine needles can help, but pH correction is an ongoing process.

Chlorosis of azalea leaves showing a yellowing of the edges

Nutrient Deficiencies

Foliage that is deficient in nutrients may appear pale and sickly. So, while you’re checking the pH, you should also check the soil for nutrients. Azaleas grow well without a lot of fertilizer, so you may not need any at all.

How to Prevent Azalea Leaf Discoloration

Check that you are meeting the cultural needs of your azaleas. Keep in mind that they thrive in loamy, well-draining soil with a pH between 4.5 and 6. A soil test will tell you if you need to add soil amendments or nutrients in the form of fertilizers.

Keep a close eye on weekly rainfall and supplement with deep soaks during dry spells. During the growing season, azaleas require about 1 inch of water per week. To help moderate moisture, use organic mulches such as pine straw and wood chips. Mulches also act as a weed suppressant and a source of nutrients as they decompose.

Azaleas thrive in dappled shade or on the east side of a building, where they can escape the hot afternoon sun.

Giving azaleas the attention they require to thrive will go a long way toward preventing leaf discoloration.

blooming whitepink flowers of an azalea plant in a garden
Alaine Connolly
Alaine has been working way too hard in horticulture since 1992, beautifying golf courses, resorts, and hotels. She is a part time landscape designer who works full time caring for a 28,000 square foot public garden. At home, she maintains her own 400 square feet plot. Alaine lives in northern Illinois - zone 5b.
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