Steve Bender
For vibrant summer color, few flowering plants can compete with thecrepe myrtle(Lagerstroemia indica).
Just look around your neighborhood.
Nearly every street in the South is lined with these blooming trees from July through September.
Credit:Steve Bender
But even the best preparation doesnt prevent some common crepe myrtle issues that can arise.
Read on for the problems we hear most about and how to fix them.
Fungal growth takes place from spring through early fall.
Also called black molds, sooty molds are due to several species of fungi.
So if youve got sooty mold, you also have an insect infestation.
Some sap-sucking insects do not fully digest plant sap.
The undigested portion is excreted as a sweet, sticky liquid called honeydew.
They milk the insects for the honeydew, which they take back to other ants for food.
Ants also transfer honeydew-excreting insects from plant to plant.
Look for aphids, scales, or leafhoppers, which excrete the sticky honeydew on which sooty mold grows.
All of these are safe, natural products available at home and garden centers.
On small plants, wipe or wash off the molds with a small sponge and water.
On large trees, use a hose-end sprayer to wash off the mold.
That way if fungus spores do travel with water droplets, theres less chance theyll grow elsewhere.
Powdery Mildew
Powdery mildew is a filmy, white fungus that grows on leaves and flower buds.
Insufficient sunlight and poor air circulation encourage development.
There are many different powdery mildew fungi.
The fungus spores overwinter on fruit trees.
Leaves infected with powdery mildew will turn yellowish or brown.
New growth may be stunted, curled, and distorted.
Fruit drops early or is dwarfed.
Flower buds drop without opening.
The first three are natural products.
You’ll probably have to spray more than once.
To prevent powdery mildew, give plants sufficient light and air circulation.
Reduce spreading by cutting back on nitrogen fertilizer, and pick off and destroy infected leaves and flowers.
The nearly universal planting of crepe myrtles in the South has made it easy for thisfungus to spread.
This fungus likes sheltered areas where breezes are blocked and the foliage stays wet for long periods.
Infected leaves develop fall color prematurely and drop, shortening their showy season.
Remove the spotted leaves as soon as you see them.
Give the tree a good spray down to wash away any remaining spores.
That will keep the fungus from reinfecting your tree or others nearby.
We have doubts, though, because the one that gets devoured every year is ‘Sioux’.
They can be found clustered in branch crotches, pruning sites, and under loose bark.
Youll find them on all parts of the crepe myrtle but rarely on the leaves.
Bark scale is a relatively new pest in the Southeastern US.
It thrives when crepe myrtles are planted in shaded areas.
They rarely kill crepe myrtles but produce honeydew which grows black sooty mold.
This black mold can completely cover foliage branches and trunks.
They can cause stunted growth and reduce the size and quantity of flowers.
Crepe myrtles grown in full sun have smaller infestations than those grown in shady locations.
Mealybug destroyers are effective in controlling bark scale.
The most effective control is a dinotefuran soil drench in the spring.
It entered this country in 1974 near Charleston, South Carolina.
These tiny beetles attack both stressed and healthy plants.
While beetles are present most of the year, major activity occurs in March.
Females bore into stems, branches, or trunks of young trees.
They lay eggs inside and introduce a fungus (ambrosia) with which they feed their young.
Females remain with their young until they mature and exit the tree.
Hatching females mate before leaving the tree to infest a new host.
The fungus clogs the plant’s water transport system, which results in wilting.
It’s much easier to detect the beetle’s presence than the insect itself.
Branches wilt and die back.
Once several beetles have invaded the plant, insecticides are not effective.
Prune and destroy infested limbs.
It’s best to remove a tree with severe damage to the main trunk.
Japanese Beetles
Japanese beetles are a non-native invasive pest.
Adult Japanese beetles are about 12 inch in length and are coppery-brown with metallic green heads.
Both the adult and the larvae of the Japanese Beetle can cause extensive damage.
The larvae primarily eat grass roots but can also feed on the roots of young crepe myrtle trees.
Non-chemical control can be done by hand-picking the Japanese beetles off the tree and dropping them in soapy water.
(This is a great way to keep children busy during the summer!)
A liquid spray of Sevin is also effective.
They vary in length from 1/16- to 1/8-inch long.
The aphids suck the plant sap out of leaves which causes two harmful effects.
This honeydew is food for the sooty mold fungi that can diminish the aesthetics of the crepe myrtle.
Also, aphids inject saliva into the leaf while it feeds.
The saliva causes yellow spots to develop on the leaf.
Aphids are susceptible to insecticides like insecticidal soaps and horticultural oils.
Another option for managing aphids on crape myrtles is to use one of the soil-applied imidacloprid products.
Always cut back to another branch, to just above an outward-facing bud, or to the branch collar.
Crepe myrtle trees experience dormancy every winter, causing them to lose their foliage and appear dead.
