Crepe myrtle trees are prolific bloomers putting out vibrant and fragrant blooms in late spring, summer, and fall.
For that to happen, it needs at least six hours of full sun. Even in a bright location where it gets its light needs met, the honeydew of aphids blocks it.
Given the size that the canopy of the crepe myrtle can grow to, companions plants are placed under it. Some of the best plants for under crepe myrtle trees are hibiscus, creeping lilyturf, and showy flowering shrubs like the Lantana and the Rose of Sharon.
These are not always directly affected by aphids. There are thousands of aphids’ species. One of the adapted species is the crepe myrtle aphid. This is a species-specific insect that only feeds on the crepe myrtle tree.
Other aphids will feed on it, however, most of the plants under and around these trees are a natural feeding ground for any garden pest.
Even if you do get host-specific aphids feeding on the tree, the plants under it will be indirectly affected by the excrements they drop.
Read on to discover the tactics that need to be deployed for crepe myrtles, and all the surrounding plants to bloom before aphids stop them growing.
How to get rid of aphids on crepe myrtles
A daily jet spray of water directed at the underside of leaves knocks the aphids off. Most are wingless and will die of starvation. Treat crepe myrtles and all plants under its canopy weekly with neem oil. This kills aphids on contact, and protects against sooty mold, which is more damaging.
The effects of honeydew on all plant leaves
Aphids and similar sap-sucking pests pierce the leaves to feed on the sugary sap. The sap inside leaves is just like sugary water. It is a rich source of carbs for soft-bodied insects.
As Newton’s law taught us: what goes in, must come out. Sap goes in, honeydew is the excrement.
This is a sticky substance that coats the leaves. Aphids do not poop where they feed. They drop their droppings to lower leaves away from their feeding ground.
Ants are a garden alarm!
A colony of aphids will leave loads of excrement on the leaves. Ants seek out that as their food source. Ants cannot and do not pierce into the leaves of plants. They eat the honeydew.
The relationship between ants and aphids is symbiotic. They rely on each other for survival.
Ants need the honeydew for food. Aphids benefit from their protection.
If the colony of aphids is big enough for an ant colony to warrant protecting them, they will fight off ladybugs and even lacewings to secure their food supply.
As the ants do not eat aphids, and the honeydew gets dropped, it lands on any plants under the tree canopy.
A trail of ants can signal that there are aphids or another sap-sucking insect nearby.
Since ants feed on the honeydew and not the sap, there will be ant trails beneath aphid colonies.
Honeydew sets the stage for black sooty mold
In the case of the crepe myrtle aphid, that can be in the tree feeding on the leaves, but the excrements can be dropping onto a hibiscus under it.
As the crepe myrtle aphid is species-specific, the colony will not migrate to the hibiscus plant, but the hibiscus will still show the symptoms of an infestation.
… Ant trails and the fungal growth of black sooty mold.
Why leaves on (and under) crepe myrtles turn black
Honeydew, being sticky, blocks the pores on the leaves of plants. It blocks sunlight, nutrients, and air putting photosynthesis on the backburner.
Essentially, every plant affected shuts down. The honeydew is more damaging than the aphids. Aphids cause cosmetic damage. The excrements they coat the leaves with are what will shut the plant down.
Not only is the mold one of the reasons for crape myrtle not blooming, but it will shut down every plant growing under the trees canopy. Hibiscus growing under the tree with sooty mold and no aphids on it, will not flower.
The black sooty mold growth on all plant leaves need to be washed with an insecticide.
If you cannot see any insects on the plant, look up. Sooty mold grows on the honeydew. That gets dropped from above.
The aphids will be hiding among leaves in the canopy above the plants with sooty mold.
Hosing and spraying organic insecticides
Neem oil and insecticidal soaps are considered safe to use, however, they are not selective and can be harmful to beneficial bees.
When spraying organic insecticides, do it before the garden gets busy with beneficial bugs visiting. Either early morning and late evening when it is dry.
Soaps and oils should not be sprayed in hot temperatures anyway because oils magnify heat and that risks leaf burn.
The all-natural solution is a garden hose with a long reach wand to spray them off with water only.
Aphids are asexual that give birth to live young that are wingless. A strong enough blast of water to knock them into the soil is enough. They are too weak to get back onto the plant.
Given the tremendous amount of foliage on crepe myrtle trees though, it is inevitable that some will remain.
For those that do linger around, hit those with an organic insecticide.
Neem oil is effective as a contact insecticide, fungicide, and miticide.
In other words, if it does not kill on contact, it will affect the reproduction rate. Repeat applications are needed, however, with each treatment, breeding is slowed. That buys you time to get on top of the infestation.
How to spray neem oil on crepe myrtle trees
To spray crepe myrtles trees, a pump-action sprayer (with at least a 1-gallon capacity) that has a long reach wand will be needed.
You will need a neem oil concentrate diluted to the ratio explained in the instructions that come with the bottle.
When spraying, the spray should be directed to the underside of leaves as that is where aphids do most of their feeding. And why their excrements hit lower leaves and all the plants under them.
Use a diluted strength neem oil soak once weekly. Daily though, hit the plant with a forceful jet spray of water directed at the underside of leaves to knock as many aphids off the plant as possible.
For every aphid that remains, they can produce up to 5 wingless offspring daily. That is why a daily hosing down is essential.
Weekly treatments of neem oil are needed to hit the stray aphids that manage to survive your artificial rainstorm.
The combo approach will eventually get rid of aphids on crepe myrtle trees and save every plant under it from shutting down because of sooty mold.
Frequently Asked Questions about getting rid of aphids on crepe myrtle trees
What is a dormant oil treatment?
Dormant oil treatment is a thick oil that is usually petroleum-based. It is mixed with an emulsifier so that it sticks to any overwintering eggs. This treatment needs to be applied early in the year before leaves emerge. Dormant oil treatments are done to suffocate overwintering eggs.
Is an Imidacloprid soil drench safe for crepe myrtles?
An Imidacloprid soil drench is a systematic insecticide. It poisons insects that eat the plant. As it is absorbed through the roots, it does take time. When the tree is in bloom, the Imidacloprid will be present in the nectar exposing the toxin to beneficial insects and garden pollinators.
Marcel runs the place around here. He has a deep passion for houseplants & gardening and is constantly on the lookout for yet another special plant to add to his arsenal of houseplants, succulents & cacti.
Marcel is also the founder of Iseli International Commerce, a sole proprietorship company that publishes a variety of websites and online magazines.