It is apparent that Central Texas loves crape myrtles. Just take a drive around and see these beauties blooming in many landscapes. They have been enjoyed in the United States for over 200 years. Shipping records from 1799 show that crape myrtles seeds were brought to the George Washington plantation. Originally crape myrtles came from Southeast Asia.
Crape myrtles are hardy and gorgeous assets to our landscapes but they are not immune to pests and disease. Powdery mildew is one disease that can plague our beloved crape myrtles. It is a fungus that attacks leaves, shoots, buds and even its flowers. The best way to prevent this fungus is to select one of the many varieties that are resistant to this malady.
There are a few insects that can plague crape myrtles. The newest one discovered to plague crape myrtles in Texas is crape myrtle bark scale. Initially diagnosed in Richardson, TX in 2004, it is believed that the culprit (Acanthococcus lagerostroemiae) migrated from Asia. Today it is found in Texas, Oklahoma, Arkansas, New Mexico, Tennessee, Georgia, Alabama, Mississippi, North Carolina, South Carolina, Virginia and Washington.
The scale is a sucking insect that feeds on the phloem (sap) of plants. As it feeds, it excretes a sugary solution known as “honeydew” (similar to aphids, whiteflies, and other sucking insects). Heavy infestations of crape myrtle bark scale produce sufficient honeydew to coat leaves, stems and bark of the tree. This honeydew, in turn, will eventually turn black as it is colonized by a concoction of fungi, called sooty mold. Although crapemyrtles rarely die as a result of crape myrtle bark scale infestation, the sticky leaves and black trunks greatly reduce the attractive appearance of the tree.
One of the first tell-tale symptoms of crape myrtle bark scale is a black sooty mold covering the trunks and branches. Another symptom is seeing the culprit adult insects on the trunks and branches. Young immature bark scale insects are difficult to see. Later as these insects mature, there will be very small tufts of white or grey noticed on the upper branches and trunk. These are actually the grey or white, oval, female scales and the smaller male scales. When these tufts are crushed, they “bleed” pink. These tufts could house dozens of eggs of the crape myrtle bark scale. They will often appear in crotches of older wood or around pruning wounds.
Control of crape myrtle bark scale is one of choice. There are several chemical treatments that can be used, however these can also be harmful to pollinators and beneficial insects we want to protect. Naturally the crape myrtle bark scale has several natural enemies, one of which is the lady beetle. This insect hero can provide about 75% suppression of crape myrtle bark scale in the landscape.
One might ask is crape myrtle bark scale in Bell County. The answer is yes. According to tamu.edu it was confirmed in July, 2015. Check out http://stopcmbs.com for more information about crape myrtle bark scale. More research is being done about this insect.
Another problem insect is the crape myrtle aphid (Tinocallis kahawaluokalani Kirkaldy), the only aphid species that feasts on crape myrtles, found from May through September. They may peak from July to early August. It, too, will create a honeydew that leads to a black sooty mold. This insect lives on the juices sucked out leaves which causes yellow spots and the leaves to drop prematurely.
There also is a primrose flea beetle that can plague crape myrtles. Adults feed on crape myrtle, evening primrose and other plants. The adult beetles will chew many holes or pits into the leaves, leaving “shot holes” in the leaves. The effect of their feeding is most severe when they attack the growing tips because this limits the ability of the plant to compensate for damage making young plants and seedlings particularly susceptible causing the plant to die or extremely stunting its growth. (https://crapemyrtletrails.org/pest-control/)
A few years ago, I had a tall crape myrtle in a prominent place in my landscape. Noticing black sooty mold on the branches, I asked a local prominent horticulturalist to help diagnose the problem. He suggested that it might be an aphid infestation, however the leaves were not turning yellow from the feeding nature of the aphid. He suggested that the treatment to return the crape myrtle to normal was more expensive in time and money than it was worth to save this plant that was planted very close to my home (well before it grew to its potential height and width). My husband and I removed the crape myrtle, mainly because it was too close to our home. That was before I learned about the crape myrtle bark scale. Today, I am wondering if the problem was caused by aphids or crape myrtle bark scale. I will never know for sure.
July 18th is the date of the next Gardening in Central Texas class, set 6:30-8 p.m. at the Extension classroom located at 1605 N. Main St. in Belton. The topic will be identification of plant diseases found in our Central Texas area and how to identify and treat these diseases which include trees, shrubs, and flowers. Our focus will be on those which are new to diagnose and have been identified in our county. These include crape myrtle bark scale, Emerald Ash borer, rose rosette, and photinia fungus. Seminars are free of charge but a $5 donation is accepted.
Class size limited to 45 attendees so register early at firstname.lastname@example.org.