By: Teo Spengler
Crepe myrtle trees (Lagerstroemia indica), also spelled crape myrtle, offer so much beauty that it’s no wonder they are favorite shrubs in Southern gardens. The petals – white, pink, red or purple – are paper thin and delicate, the blooms enormous and beautiful. These lovely trees are usually trouble free, but even crepe myrtles have a few issues that crop up. What is crepe myrtle blight? Read on for information about blight and ways of treating blight on crepe myrtle.
What is Crepe Myrtle Blight?
Crepe myrtle tip blight results from a fungus that causes leaves near the tips of the tree branches to turn brown in spring or summer. Look closely at the infected foliage to see the small black spore-bearing bodies.
Crepe Myrtle Blight Treatment
Treating blight on crepe myrtle begins with proper care and cultivation practices. Like many fungal diseases, crepe myrtle tip blight can be discouraged by following a few simple rules about caring for your trees.
Crepe myrtle trees need regular irrigation to bloom and thrive. However, they don’t need overhead watering. Overhead watering moistens the foliage which encourages the fungus to develop.
Another good way to use prevention as part of crepe myrtle blight treatment is to encourage air circulation around the plants. Prune out branches that cross and those that head into the tree center to allow air into the crepe myrtles. Don’t forget to sterilize your pruning tool by dipping it in bleach. This avoids spreading the fungus.
Another action you can take to prevent the fungus is to remove old mulch regularly and replace it. The crepe myrtle tip blight fungus spores collect on that mulch so removing it can prevent an outbreak from recurring.
Before you begin using fungicide as a crepe myrtle blight treatment, make sure your tree’s problem is crepe myrtle tip blight. Take in leaves and twigs to your local garden store for advice on this.
Once the diagnosis is confirmed, you can use fungicide to help your trees. Spray the infected crepe myrtle trees with copper fungicide or lime sulfur fungicide. Start spraying when the leaf tip symptoms first show up, then repeat every 10 days during wet weather.
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Problems of Crepe Myrtle
Tree/shrub Tops Blacken, Die Back In Spring means Cold Weather
In some northern areas crape myrtles are victims of cold snaps which kill their tops. Their roots are generally cold hardy, however, so simply prune off the dead material early in the spring before growth starts. The plant will sprout new growth and bloom on schedule.
Crape myrtle Fails to Bloom indicates the plant was Pruned Too Late
Crape myrtles bloom on wood that is form in the current growing season. If pruning is delayed until the new shoots have begun to grow and they are cut off, flower buds will not form. The tree is basically all right and will bloom next season. Always prune before growth starts in the spring.
Foliage Curls, Turns Yellow shows Aphids
Check crape myrtle stems and leaves for bunches of soft-bodied, pear-shaped, insects a little bigger than the head of a pin. They may be white, yellow, red or brown. These are aphids, which suck sap from leaves and stems of crape myrtles, causing them to curl and turn yellow. As they feed they secrete a sticky "honeydew" on the foliage that coats it. It, in turn, encourages sooty mold fungus, which then coats the leaves in black.
To dislodge light aphid infestations, spray the undersides of foliage vigorously with water three times, once every other day, in the early morning. If aphids persist, spray them with insecticidal soap every 2 to 3 days, making sure to hit the insects with the spray. As a last resort, spray them directly with encapsulated pyrethrum. Take care to use pyrethrum late in the day to minimize killing honeybees and other beneficial insects that reside in the yard. If serious aphid problems recur every year, spray dormant oil spray on the crape myrtle trunks and stems late in the winter before leaves begin to develop. This will smother overwintering aphid eggs.
For more information see file on Controlling Aphids.
Leaves Stunted Coated With White Powder indicates Powdery Mildew
This fungal disease is a serious problem on crape myrtles from Maryland to Florida and out to Texas and in the North on trees planted near the seashore or other cool, foggy areas. It also sometimes strikes these plants which are in shady locations. It winters over in dormant buds and shows small white circles on new leaves when spring arrives. Then it spreads to new, young shoots and eventually to the larger leaves. Affected plant parts are coated with a dusty white growth and the leaves are stunted and thickened. Sometimes they are only 1/3 normal size. Stems are stunted, flower buds fail to develop. Diseased plant parts sometimes drop off in a week or two and the plant may recover and produce new growth when hot weather arrives. Where powdery mildew is common, spray trees with lime sulfur in early spring as the buds break. Repeat this spray 2 weeks later. If the infection persists, spray all affected plant parts with wettable sulfur or dust with sulfur. Plant in open, airy locations with plenty of sun. Mildew resistant varieties of crape myrtle are hybids `Biloxi', `Miami', and `Wichita'.
For more information see file on Controlling Fungal Disease.
Leaves Near Stem Tips Turn Brown shows Tip Blight
A tip blight caused by a fungus sometimes attacks crape myrtles. Leaves near the branch tips turn brown in late spring or early summer. Tiny black spore-bearing bodies appear on infected leaves. Spray plants with copper fungicide or lime sulfur fungicide when symptoms first appear and then every 10 days in wet seasons. Avoid overhead watering which keeps foliage moist and fosters the disease. Prune to increase air circulation around plants, taking care to sterilize pruning tools by dipping them in household bleach to avoid spreading the disease. Because the fungus spores collect on the mulch beneath the shrubs, removing the old mulch and replacing it with fresh material may help prevent an outbreak from recurring.
If this blight is a common problem every year, prune and destroy affected plant parts in the early spring. Spray a copper fungicide or lime sulfur in four applications: (1) after the dead leaves and dying branches have been removed and before growth starts in the spring (2) when growth is half completed (3) after spring growth has been completed and (4) after fall growth stops. Take care to determine if the crape myrtle twigs are turning brown from frost damage rather than disease.
For more information see file on Controlling Fungal Disease.
]Dead Blotches on Leaves means Leaf Spot
Various leaf spot fungi cause yellow, brown or black dead blotches on crape myrtle leaves. These blotches frequently run together. Heavily infected leaves then turn yellow or brown and fall prematurely. Cool, moist weather encourages these diseases, especially when new leaves are developing. Shake out all fallen and diseased leaves from the center of the crape myrtle and destroy them. Remove all dead branches from shrub centers, especially in crape myrtle hedges to allow better aeration. Mulching helps prevent the disease from splashing up from the ground and infecting plants. Spray at weekly to 10-day intervals with sulfur or Bordeaux mixture or other copper fungicide, particularly if weather is damp. Spray between rains. Dig up and discard seriously infected shrubs with their root system and soil ball in a bag for the trash. Clean up all debris, infected leaves, etc. to avoid spreading the fungus.
For more information see file on Controlling Fungal Disease.
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How to Combat Blight on Trees
Blight is a quick and deadly tree disease that can potentially affect almost any tree in the U.S., which makes it a huge problem. Knowing how to combat blight is essential. If you don’t treat this problem as soon as it strikes, it can kill not just one tree but entire tree populations. There are several types of tree blight, but the treatment is generally the same for all these different diseases.
Fire blight causes discoloration, usually on the bark of trees, though it can also affect blossoms and roots. There is no cure for fire blight. Once it affects your trees, your only hope is to completely eliminate the blight by pruning it off the tree. To successfully remove fire blight, you actually have to over-prune. You need to cut 12 to 18 inches above and below the areas of the tree that are visibly affected.
Diplodia and Dothistroma Blight
Almost all species of pine can potentially be infected with diplodia and dothistroma blight. Diplodia blight makes needles of pine trees turn brown. This blight also stunts growth in new shoots, which can ultimately make the tree look malformed. Dothistroma blight kills needles on evergreen trees. Over time, dothistroma blight can kill a tree if it's not treated.
At first signs of either one of these types of blight, the infected tree should be pruned. Cut away all infected areas of the tree, and cut several inches above these areas to prevent the blight from spreading and ensure it has been fully removed. Once all the pruning is complete, use a fungicide to kill the blight and prevent future outbreaks.
Don't let the name of this tree blight mislead you. Hardwood trees of all kinds, not just chestnut trees, can be infected with chestnut blight. This blight is incredibly deadly and capable of killing entire populations of hardwood trees. There is no cure for chestnut blight, so prune diligently when it pops up.
A type of blight specific to elm trees, this fungal infection can be spread by beetles. As a precaution, you can inject your elm trees every two to three years with a protective treatment, which will at least reduce their chance of contracting the disease.
One of the most pernicious and dangerous kinds of blight, this wilt affects many kinds of plants, from hemp to vegetables to maple trees. The tricky part to addressing Verticillium wilt is that it lives in the soil, so pruning dead branches stems with browning leaves might not be enough. In extreme cases, you might have to remove your tree, though you can try fumigating your soil with chloropicrin first.
General Tips for Treating Blight
When pruning away potentially infected branches and other parts of trees, dip your pruning shears in bleach before you make each cut. This will help prevent the blight from spreading to healthy parts of the tree. Once all the infected areas of the tree are cut away, treat the tree with fungicide to prevent the blight from spreading and infecting new parts of the tree. This method is effective for all types of tree blight.
There are many other types of tree diseases and problematic bacteria that can potentially kill trees, stunt their growth, or ruin their foliage. If your initial treatment does not work, you may have a different type of tree disease that isn’t blight at all. When in doubt, call in a professional gardener or tree specialist to find out how to stop your tree disease.
Combat Blight on Your Trees
As soon as you think you have a blight problem, start combating it. If you don’t act quickly and decisively to treat blight, it’s not just your trees that can potentially be affected. Blight can spread to every tree in your neighborhood, changing the landscape for generations. This is a dangerous problem, but you can fight it with pruning, fungicide, and a little bit of time and care.
Common Types of Tree Blight
The certified arborists at SavATree are experienced tree doctors who diagnose and treat blight for many types of trees, including pine tree varieties, elm tree varieties, dogwood tree varieties, maple tree varieties, cherry tree varieties, apple trees, ash trees, willow trees and many others. Below are some of the most common types of tree blight.
Fire blight is a specific bacterial infection that commonly affects orchard trees, such as apple trees, and which may impact the production of edible fruit. SavATree’s fruit tree disease treatments follow a protocol developed by several leading universities, utilizing the minimum number of treatments required to facilitate a productive harvest.
Diplodia blight affects conifers of all kinds including ornamental evergreen shrubbery. It is one of the most common types of pine tree diseases and can affect any of the pine tree varieties. Symptoms of this kind of tree blight include stunted growth of new shoots with brown needles.
Dothistroma blight is another common type of pine tree disease and affects many different pine tree varieties. It is a foliar disease, which means that it infects and kills the pine tree needles. It is a serious form of tree blight that can kill the tree and require tree removal.
Anthracnose and Leaf Spot Diseases
Anthracnose is a type of tree blight which affects many hardwood tree varieties. It is common among dogwood trees including white dogwood trees and pink dogwood trees. It also affects oak tree varieties and sycamore trees. This tree fungus grows in cool, damp weather such as early spring or late fall. If left untreated over time, this type of tree blight can kill these hardwood trees or cause a need for tree removal. Symptoms of these tree diseases include dead areas or spots on the tree leaves.
Maple Wilt (Verticillium Wilt)
Maple wilt is a type of tree blight that can affect many different maple tree varieties, including the Japanese red maple tree, sugar maple tree and other varieties of red maple trees. This type of tree disease is caused by a fungus that grows in the soil and can have a devastating effect on maple trees, sometimes even requiring tree removal. Symptoms of this type of maple tree blight include brown-looking leaves or large branches that have died.
Chestnut blight is caused by a fungus and is notorious for causing the American chestnut tree to become nearly extinct since it was discovered in the early 1900s. Arborists continue to work to restore chestnut tree populations, especially in Massachusetts.
Dutch Elm Tree Disease
Dutch Elm Disease has felled feature elm trees on many northeastern landscapes. As a preventive measure, specimen elm trees can be successfully trunk injected during the spring/summer with a treatment that will prevent the development of the Dutch Elm Disease fungus for up to three years. However, this tree disease treatment is not always effective against previously infected trees.
Sycamore Anthracnose is a common type of tree fungus that results in extensive defoliation, shoot dieback, and twig death of your sycamore trees especially when extended periods of cool wet weather occur in the spring. Because it is very difficult to control through conventional disease treatments, SavATree uses a macroinfusion system that will prevent infection of your sycamore specimens for up to three years.
SavATree can also help prevent and treat other common tree fungus diseases including weeping cherry trees and oak tree varieties. Call today for a complimentary consultation with SavATree’s fully trained professionals and certified arborists. Click here to contact the office nearest you.
Apply Ferti-Lome Tree & Shrub Systemic Insect Drench. Mix with water as directed, and apply in a band along the drip line of the plant, as a soil drench. To measure the crapemyrtle, add up the circumference of all trunks at chest high (about 4.5 feet off the ground). For example, if you have 5 trunks and the trunk circumference is 4 inches each, then you have a total of 20 inches in circumference.
The drench will need to be applied to the drip line of the plant. The drip line of the plant is considered to be the outer circumference of the plant branches and inward toward the trunk several feet (see diagram above). In order to apply this 20 ounces properly, it will need to be mixed into several gallons of water so that there is enough volume to be applied in a 3-4 foot band from the drip line in towards the tree trunk all the way around the plant.
How to Treat Mildew on Crape Myrtle
The best time to prune crape myrtles is in the winter, when they are dormant, or in the spring, before they have set new blooms.
When you water your trees, direct the water at the base or use drip hoses. Sprinklers can create conditions in which mildew thrives.
Avoid high-nitrogen fertilizers, which can encourage mildew growth. Choose organic or slow-release fertilizers instead.
Mildew spreads rapidly. Treat your crape myrtle at the first sign of trouble to prevent serious damage.
If your crape myrtle's dark green leaves have turned white, your tree might be infected with mildew. Crape myrtles are prized where they can be grown for their beautiful flowers, long blooming season, and attractive, interesting bark. Unfortunately, some crape myrtle cultivars are susceptible to powdery mildew. Mildew is a fungus the white powder you see is made up of spores. Mildew thrives in warm, moist conditions. It is best to prevent the growth of mildew, but if your tree is already infected, following these steps will help you restore it to its former beauty.
Confirm the problem. Examine your crape myrtle's leaves. Are they coated with a white, powdery-looking substance? Does the powder extend down to the stem, and are there any discolored or dead areas underneath the powder? If so, your tree has mildew.
- If your crape myrtle's dark green leaves have turned white, your tree might be infected with mildew.
Apply fungicide. Find a fungicide specifically formulated for mildew on crape myrtles or use a generic fungicide that contains one of these ingredients: propiconazole, tebuconazole, thiophanate-methyl, myclobutanil or triadimefon. Apply as directed keep applying until the mildew has retreated.
Consider an organic alternative. If you prefer to use a nonchemical fungicide, choose one that contains neem oil, sulfur or potassium bicarbonate. According to the National Arboretum, horticultural oil can also control powdery mildew. Apply as directed.
- Find a fungicide specifically formulated for mildew on crape myrtles or use a generic fungicide that contains one of these ingredients: propiconazole, tebuconazole, thiophanate-methyl, myclobutanil or triadimefon.
- If you prefer to use a nonchemical fungicide, choose one that contains neem oil, sulfur or potassium bicarbonate.
Prune the tree. According to Mississippi State University, pruning will increase air circulation, decreasing humidity and making it less likely that mildew will spread. Prune any dead branches, but also prune any small, twiggy undergrowth near larger branches. After each cut, dip your pruners in white vinegar to kill any spores.
Take preventive measures. To avoid mildew in the future, water only in the mornings and keep trees pruned. Applying fungicide to new growth in the spring can also help prevent mildew.
- According to Mississippi State University, pruning will increase air circulation, decreasing humidity and making it less likely that mildew will spread.
Research new crape myrtles. When planting new crape myrtles, consider mildew-resistant cultivars. Plant the trees in full sun, and do not crowd them with other plants.
What Are Those White Specks on My Crepe Myrtle?
A new pest threatens the South's favorite flowering tree.
There's no denying the crepe myrtle' supremacy as the number one ornamental tree in our region. It seems everywhere in the South a crepe myrtle could be planted it has been. Such popularity comes at a price, however, as it makes it easy for a pest to hop from one tree to another. That's just what's happening now with a new insect pest called the crepe myrtle scale.
Crepe myrtle scale arrived here a few years ago as an accidental import from Asia. Since then, it spread rapidly. It's easy to spot. It looks like a white speck stuck to the bark of a trunk or branch. Thousands of scales encrusting the bark will literally turn it white.
These insects survive by building protective shells over themselves on the bark and sucking the plant's sap. Then they secrete a sticky honeydew that black mold grows on. Under the shells, female scales lay lots of eggs that hatch out spring and summer and worsen the infestation. Infestation rarely kills the target tree, but it does turn it into an ugly mess.
WATCH: What's Wrong With My Crepe Myrtle? 4 Common Problems
What should you do if you discover crepe myrtle scales on your tree now? First, after its leaves drop, apply dormant oil to the trunks and branches. This will smother both adult and immature scales. Next, in late March, apply a systemic insecticide called Bioadvanced Tree & Shrub Insect Control to all your crepe myrtles according to label directions. The crepe myrtle will absorb the insecticide and all scales feeding on it will die.
Crepe myrtle scale has no natural enemies here yet, so this is the only effective control. Once again, Grumpy has saved your garden from oblivion. You're welcome.