What is the Best Insecticide for Crepe Myrtle Bark Scale?

May 27, 2025

Crepe myrtles are spectacular trees. Like any plant lover, I also had my ups and downs with plant pests. There is one, however, that I have constantly battled with, the Crepe Myrtle Bark Scale. Over time, I learnt a lot through different trials and errors, some productive and others not so much.

If your crepe myrtle trees develop white tufts of fuzz and sticky black mold, alongside stunted blooms, you can be certain that this pest is meddling with your trees. In this article, I’ll share everything I have learned from these experiences.

What is Crepe Myrtle Bark Scale (CMBS)?

CMBS is a soft-bodied insect that sucks the sap of crepe myrtles. Discovered in Texas in 2004, it is now located within the southern United States and is spreading towards the north. These pests are identifiable by their white to gray waxy coating. It is often found on the bark of the trunk and branches.

How Does CBMS Cause Damage to Your Crepe Myrtle?

Encouragement of Sooty Mold: CMBS honeydew secretion leads to the black sticky mold known as sooty mold, which encourages formation on leaves and tree bark.
Encouragement of Sooty Mold: Affected Sooty Macrosiphum gesneriae scales cause Mjaries viridis to gradually weaken.
A Reduction in Tree Vigor: The intricate feeding tasks performed by the CMBS siphon and serrate processes are bound to weaken tree vigor and flowering rate.
Aesthetic Damage: Sooty molds forming in the bark make the tree unsightly.

According to research from the University of Arkansas Extension, heavy infestations can reduce bloom quality by over 50%.

The Best Insecticides for Treating Crepe Myrtle Bark Scale

Accompanied by arborist consultations, testing systemic insecticides proved to be the most effective. They work like magic in fending off the pests within the arms of the trees’ vascular circulatory system.

Here are some of my top suggestions you can go for:

1. Imidacloprid (e.g., Bayer Tree & Shrub Insect Control)

This is the most recommended option. It’s a neonicotinoid that affects sap-feeding pests such as CMBS.

Application: Soil Drench or Root Soak.
Effectiveness: Excellent when applied in early spring, before new growth.
Duration: Protects the tree for up to 12 months.

Tip: Make sure to water the soil well after applying to improve absorption.

2. Dinotefuran (e.g, Safari 20SG)

Dinotefuran acts quicker than imidacloprid and is more appropriate for active infestations.

Application: Soil Drench or Trunk Spray.

Effectiveness: Fast-acting (2-3 weeks).

Duration: Lasts for one full season.

Note: While this option is more expensive, it is much more effective for severe infestations.

3. Bifenthrin or Permethrin (e.g, Ortho Tree & Shrub Insect Killer)

These suppressing insecticides are useful for knockdown control, but don’t offer prolonged protection.

Application: Direct spray on visible scales.
Effectiveness: Short-term, capable of knock-down, but repeat application is often necessary.
Good For: Supplementing systemic insecticides such as the ones previously mentioned.

Systemic insecticides applied in early spring will reduce the CMBS population over 90% within two months, according to Mississippi State University.

How to Apply Insecticides for Crepe Myrtle Bark Scale?

It may appear that applying insecticides is an easy task, but efficiency depends on proper application. Personally, it is sensible that the timing, technique, and even climate play a role. In your case, if the execution is rushed or done before the correct time, the expectations may not be met.

Let’s go over the methods of applying it effectively.

1. Best Soil Injection Method (Most Effective For Systemic Insecticides)

My top choice for insecticides is always based on imidacloprid and dinotefuran. The scale insects within the tree are slowly killed off because the imidacloprid or dinotefuran is absorbed by the roots and is then moved up through the vascular system.

Here is how you do it:

Follow the label guidelines step by step, and they should provide you with an insecticide mixture. Regarding imidacloprid, a typical treatment is 1 ounce per inch of the trunk diameter, with 1-2 gallons of water.
Using a calibrated sprayer, inject portions of the mixture evenly into the ground surrounding the tree at the base and also a few inches away from the trunk.
To encourage root absorption of the product, the soils should be saturated thoroughly post-application.
The ideal period for application is early spring, prior to the emergence of new leaves. This will guarantee that the tree takes up the chemical while pushing out new growth.

Here are some pro tips that will come in handy:

Don’t apply during extremely dry or frozen conditions.
Apply more evenly and slower to avoid runoff.
Do not expect instant results as these products take time, typically 2-4 weeks to show results.

2. Spray Trunk Method (For Active Infestation Needs)

If I’m combating a late-season outbreak or severe infestation, I utilize trunk sprays. This method is often done with dinotefuran as it absorbs faster through the bark than imidacloprid.

Here is the process:

Choose a calm, dry day, as windy conditions will waste spray and cause harm to the surrounding foliage.
With a garden or backpack sprayer, add 12-24oz per gallon of water, depending on the size of the tree/label instructions.
Cover all surfaces of the lower trunk, starting at the first primary branches up to 1 meter.
Avoid base watering for 1 day to allow the spray to dry in order to avoid dilution.

Best Timing: Mid-spring to early summer is the best season. However, late summer can also be used as a secondary generation scale insect suppressant.

Caution: Don’t spray during Pollinator peak bloom periods so you can protect pollinators.

3. Procedure For Foliar Spray Application (Effective For Light Infestation or Spot Treatment)

Permethrin, horticultural oils, and bifenthrin can be used to prepare foliar sprays that can be effective for the treatment of visible scales and the reduction of honeydew.

Here is how you can apply this:

Assemble the product according to the label rates. Generally, a few tablespoons are mixed for every gallon.
Apply the spray to the leaves, branches, and visible scale clusters until dripping.
In case of stubborn infestations or emergence of new insects, respraying should be done after seven to fourteen days.

Pro Tip: Always test a small area for leaf burn or phytotoxicity as well.

Timing of Application

The timing here is a crucial factor. Here is a quick guide:

Season	Best Method	Purpose
Late Winter	Horticultural oil spray	Smother overwintering eggs
Early Spring	Soil drench or trunk spray	Pre-bloom systemic treatment for prevention
Late Spring to Summer	Trunk or foliar spary	Knock down active infestation
Fall	Soil drench (optional)	Prepare for next season’s outbreak

Alternative Treatments for Crepe Myrtle Bark Scale

Sometimes, I like to take a more natural approach before going full-force with chemicals. Here are some effective alternatives:

1. Manual Removal

There are several methods to gently scrub bark clean while protecting beneficial insects. As such, cleanings should always remove any living pests.

Scrubbing away at the infestation can drop numbers significantly.
A soft brush paired with a weak soap solution works best, which means not concentrated.
Gently scrub the bark to eliminate scales as much as possible.
Make sure to rinse to prevent build-up as much as possible, leaving water standing.
Make sure targeting pests are not present.

2. Horticultural Oil

It is a useful option for suffocating the insects along with their eggs.

Best used in the dormant season (late winter)
Use water mixed with 2% horticultural oil
Apply to the trunk and branches completely

3. Lady Beetles

Pest for CMBS, which are lady beetles, are super useful.

Chilocorus cacti are particularly useful for the fight against CMBS.
If you need to apply your chemicals for them, aim in early spring.
Use alongside small amounts of insecticides to ensure the pests do not perish.

According to the 2021 study conducted by Texas A&M, they recorded lady beetles to have destroyed 40% of CMBS in maintained urban areas.

Preventing Crepe Myrtle Bark Scale Infestation

After taking care of an active pest problem, prevention shifts your priority. I now check my trees and take action once a year.

Here’s what you can do to stay away from CMBS:

1. Routine Inspections

Look for scales and inactive black mold on the trunks
Lower branch and trunk bases should be examined monthly
Timely actions reduce treatment complexity

2. Avoid Over-Pruning

Excessive pruning causes Crepe myrtle (crepe murder) trees to become unhealthy and increase pest problems.
Only prune dead wood or crossed branches
Improve air flow while promoting the tree’s natural shape

3. Fertilizer Application

Feeding them too much nitrogen will invite sap-eating pests.
Use slow-release nitrogen-balanced fertilizers.
Apply once in spring and monitor growth.

4. Natural Predators Inducement

An insect-welcoming garden should be created.
Flowering herbs like dill or yarrow should be sown.
Insecticides should not be used during peak bloom.

Final Thoughts

Eliminating the Crepe Myrtle Bark Scale is difficult but manageable with the proper tools. In my experience, preventing infestations and using imidacloprid has proven most effective, while active ones respond best to dinotefuran. Combining those with some manual love and eco-friendly elements will ensure your crepe myrtles are stunning and healthy.