By: Mary H. Dyer, Credentialed Garden Writer
What is bark scale on crepe myrtles? Crape myrtle bark scale is a relatively recent pest that is affecting crepe myrtle trees in a growing area across the southeastern United States. According to Texas AgriLife Extension, this harmful pest is newly introduced from the Far East.
Adult white scale is a tiny grey or whitish pest easily identified by its waxy, crust-like covering. It can appear anywhere, but is often seen on branch crotches or near pruning wounds. If you look closely under the waxy covering, you may notice clusters of pink eggs or tiny nymphs, which are known as “crawlers.” Female pests exude a pinkish liquid when crushed.
Crepe myrtle bark scale treatment may require several different techniques, and management of the pest requires persistence.
Scrub the pests away – It may sound odd, but scrubbing the tree will remove many of the pests, thus making other treatment more effective. Scrubbing will also improve the appearance of the tree, especially if the scale has attracted black sooty mold. Mix a light solution of liquid dish soap and water, then use a soft brush to scrub the affected areas – as far as you can reach. Similarly, you may want to use a pressure washer, which will also remove loose bark that creates a handy hiding place for the pests.
Apply a soil drench – Drench the soil between the tree’s drip line and the trunk, using a systemic insecticide such as Bayer Advanced Garden Tree and Shrub Insect Control, Bonide Annual Tree and Shrub Insect Control, or Greenlight Tree and Shrub Insect Control. This treatment works best between May and July; however, it may take several weeks for the substance to make its way throughout the tree. A soil drench will also control aphids, Japanese beetles and other pests.
Spray the tree with a dormant oil – Apply dormant oil generously, using enough oil to reach cracks and crevices in the bark. You can use dormant oil between the time the tree loses its leaves in fall and before new foliage emerges in spring. Application of dormant oil can safely be repeated while the tree is still dormant.
If your crepe myrtle is affected by white scale, it may develop black sooty mold (In fact, the sooty, black substance may be the first sign of white scale on crepe myrtles.). This fungal disease grows on the sweet substance excreted by white scale or other sap-sucking insects such as aphids, whiteflies or mealybugs.
Although sooty mold is unsightly, it is generally harmless. Once the problem pests are controlled, the sooty mold problem should resolve.
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Read more about Crepe Myrtle
Crape myrtles are one of our most beloved ornamental trees here in the Dallas area. Their stunning summer blooms are something we always look forward to each year. Crape myrtles are drought tolerant and relatively easy to care for. And while they are generally thought of as a traditional, old fashioned shrub or tree, we feel they can also be used in more modern landscapes in their natural form as their trunk forms and bark is quite striking.
However, no plant is bullet-proof when it comes to pest and diseases. And, certain insects are attracted to specific plants so, when large numbers of one plant species are used in an area, it can often lead to new concentrated outbreaks of the insect.
Such is the case with Crape Myrtle Bark Scale (CMBS). This is a relatively new pest to the Dallas/Fort Worth area and while it is commonly found on crape myrtles, if left untreated, it can also spread to surrounding shrubs and trees such as beautyberry, boxwoods, cleyera, fig, persimmon and pomegranate. Scale insects can do a lot of damage in a small amount of time. And, they’re tough to get rid of.
Photo courtesy of Soils Alive. Visit their site at www.soilsalive.com
What is Crape Myrtle Bark Scale?
While the exact species name of this is insect has yet to be confirmed, it is thought to be of the Eriococcus family. The scale insects themselves are a white to gray color the females ooze a pink to red liquid when crushed. Dozens of pink colored eggs can be found under the waxy webbing the adults leave behind. Adults are often found at oozing cuts or wounds on the tree or shrub.
Much like other scale insects it excretes a sticky “dew” that coats leaves, trunk and limbs of the infested crape myrtle.Unsightly sooty mold then grows on top of the dew, causing even more problems. While the sooty mold itself doesn’t necessarily do a lot of damage, when it grows on the leaves it can block them from photosynthesizing and reduce plant vigor.
A large infestation of CMBS can leave tree can leave a tree weakened and more susceptible to other pests and diseases.
Removing CMBS from Crape Myrtles.
While a fully effective treatment is not yet available for CMBS, there are some good cultural practices you can perform in the landscape to reduce pest pressure.
If you find a population of crape myrtle bark scale on your trees or other landscape plants, follow the recommendations above. If the plant looks stressed, give us a call and we can perform a full property inspection to identify pest issue and make treatment recommendations.
We Texans sure do love our crape myrtles, unfortunately so does this fairly new pest to North Texas called bark scale. Do not fear though, as it’s easy to treat. Crape myrtles are a very hardy trees with lots of reserves, so it would take several seasons of bark scale for the tree to succumb to this pest. Bark scale originates from China and was brought to the U.S. in 2010. A&M has identified this pest as Eriococcus lagerstroemiae, and suspects that it was brought into the U.S. on a crape myrtle plant.
Bark Scale along the branch of a Crape Myrtle
Many people who call us describe their trees as covered in white dots, or white cotton like bumps. They often think the white dots are a fungus, but it is in fact a bug. If you smash one when it’s alive it will actually ooze a reddish-pink liquid. You will oftentime see black sooty mold in addition to the white bark scale. Black sooty mold literally looks like black dust on your leaves and bark. The scale sucks the sap from your branches and tree trunks and then the sugars and yeast in the sap attracts the mold. They go hand in hand, but black sooty mold is really just a cosmetic issue. Treatment for the black sooty mold is not recommended and once the scale is terminated then the black sooty mold will disappear as well.
To kill the scale we recommend Bayer Advanced Tree and Shrub Protect and Feed Concentrate. It comes in granular and liquid form, and provides 12-month long-lasting systemic protection against the scale. The application rate depends on the tree trunk size, so you will just need to measure around the tree trunk and then pour the appropriate portion of granules or liquid around the base of the tree. Please read Bayer’s label for application rates needed for your tree, and for additional information. This product is readily available online and at most local home & garden stores such as Lowes and Home Depot.
Bayer Advanced Tree & Shrub Protect & Feed
I do want to mention that we are in no way paid or sponsored by Bayer. Over the years we have just found their products to be the perfect fit for our customers needs. Generic brands might be available, but just make sure they contain Merit. The best time of year to treat is between May-July when the scale are most active. After the scale has died you will just see a white shell as shown in the pictures above and you will not be able to see any pink coming from the scale once smashed. The white shells often take a while to fall off but you can gently brush them off to make the tree cosmetically more attractive.
Flower Cluster from a Tuscarora Crape Myrtle
Crape myrtles are still a tree that we highly recommend for North Texas as they are adaptable to a wide range of soil types, heat tolerant, and drought tolerant. Occasional pests here and there are going to happen to all trees as some point, but this is super easy to treat. Crape myrtles are also know for their resistance to powdery mildew, and can thrive in the sun and part shade.
I hope you have found this information helpful. I will be sharing more information and treatment plans for other common North Texas pests as they come about. The scale pictures were taken by my talented photog friend, Lauren.
Cercospora is a leaf spot fungus that used to be fairly uncommon, but isn't anymore. Grumpy has a theory that the nearly universal planting of crepe myrtles in the South has made it easy for this fungus to spread. What happens is that in mid- to late summer, angular, brown spots form on the oldest leaves. These leaves then develop fall color prematurely and drop. By fall, the tree may be completely defoliated, except for a few newer leaves at the top. Fortunately, this seems to cause no ill effects the next year.
Solutions: This fungus likes sheltered areas where breezes are blocked and the foliage stays wet for long periods. Grumpy knows this, because the one he planted in front of his house gets eaten up by leaf spot every year, while the one growing in the middle of the lawn is hardly touched. Some websites claim certain selections are resistant, such as ‘Apalachee,' ‘Catawba,' ‘Sioux,' ‘Tonto,' ‘Tuscarora,' ‘Tuskegee,' and ‘Yuma.' Grumpy has his doubts, because the one that gets devoured every year is ‘Sioux.' What to do? Plant crepe myrtles in open, sunny spots where air circulates freely. If necessary, spray with Daconil, Immunox, or Natria Disease Control when spots begin to appear.
Before you decide to plant a crepe myrtle, it is important to know about the common diseases that afflict the tree.
The common garden pests that infect crepe myrtle are aphids. They affect flowering plants and fruiting trees. Aphids are small soft, oval-bodied insects that are a dull yellow in color. They suck out plant sap from tender leaves. After consuming the sugar-rich sap, they excrete a yellow liquid called honeydew. The leaves that are attacked by these tiny pests develop yellow spots mostly on the undersides. These leaves tend to dry out and wilt. Sometimes, certain aphid species cause galls (swelling of plant tissues) on crepe myrtle that is round or spindle-shaped. These galls are full of aphids in different stages of their life. When the crepe myrtle tree has a heavy infestation of aphids, it causes a lot honeydew to accumulate on the tree. This attracts other pests, insects, ants, wasps, mold fungi, and flies. Thus, it is very important that you take immediate steps for controlling aphids.
» Insecticide sprays like Cyfluthrin and Bifenthrin can be used to control aphid populations.
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» Alternately, insecticidal soaps can be used for removing the aphids. The best part about this is that these soaps kill the pests while retaining the beneficial insects.
» You can use lady bugs and lacewings to control these aphids. These insects eat up the aphids and help control their growth.
Sooty mold indicates the presence of insect infestation. This is a charcoal black fungus that covers the surface of leaves, fruits, twigs, and branches of the trees. This fungus does not cause any pathogenic problems on the tree. It gets its nourishment by feeding on the insect honeydew. When the sooty mold grows thick, it covers the entire leaf. Thus, the tree is unable to carry out photosynthesis. Pests such as whiteflies, scale insects, and aphids produce honeydew. You need to use insecticides to get rid of insects as well as the mold.
Yellow and orange spots on the upper side and whitish gray spots on the underside of the leaves indicate cercospora leaf spots. The yellow spots appear due to the toxins produced by the fungus and the gray white spots underneath the leaf are the fungal spores. This infection is caused by a fungus cercospora beticola. This is a fungal infection that occurs in moist weather. It can cause complete defoliation of the tree and affect growth of younger trees. You need to plant the trees in sunny areas with good air circulation. You can use a fungicide to get rid of infestation.
One of the most common diseases that affects crepe myrtle is powdery mildew. It causes white or grayish powdery coat on the leaves. Initially, the infection begins as sporadic, circular, and powdery white spots. As the infection spreads, these tiny spots become larger. Soon, the powdery mildew spreads over the entire leaf. This fungal infection inhibits the growth of new leaves and flowers. It may also lead to stunted tree growth. If you find few twigs, leaves, or branches affected by powdery mildew, prune them immediately. Heavily infested trees need fungicide for treatment. You can also try looking for mildew-resistant varieties when choosing the tree.
The Japanese beetles are inch-long pests that love to feed on the foliage and flowers of the crepe myrtle tree. You need to get rid of both the larvae as well as the beetles, to save your tree. You can use insecticides and insect traps for controlling Japanese beetles.
If you take good care, then you can avoid these problems. The special care helps them look the best in your garden.