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How To Remove Black Sooty Mold

If you’re having problems with black sooty mold on your crepe myrtles or plants, here are a few guidelines and proven tips to help you get rid of it.

Black sooty mold is not harmful to humans but if you see sooty mold starting on your plants, it is best to treat it as soon as possible. The longer it stays, the more area it covers and the harder it is to get rid of. It can grow and cover your entire plant as well as reach other plants nearby.

Black Sooty Mold won’t always kill the plants, but besides looking unsightly, it can weaken the plants. It weakens them by covering the chlorophyll filled leaves and blocking out the sunlight used by the plant in photosynthesis.

What Causes Black Sooty Mold?

Black sooty mold is actually an airborne fungi spore that latches on to the sweet sticky liquid called honeydew, which is secreted by leaf and bark feeding insects.

On Crepe Myrtle Trees and most other plants where it occurs, the culprit here is either sap sucking Aphids or Bark sucking Scale.

scale pic from Salisbury Greenhouse

When they suck the sap, they excrete a thick gooey sugary substance called honeydew. The spores attach to this and grow, forming a thickening black sticky surface which resembles soot from the result of something burning. Hence the name: Sooty Mold.

If you’ve ever been under a crepe myrtle tree branch, and you feel something dripping on you like it’s raining, this is the aphid’s excretion. Nice, huh?

Aphids are not a welcome insect by any means, but there are going to be a few tolerable amounts on any crepe myrtle. The appearance of sooty mold on plants can sometimes be an indication that you have an over population of aphids or Scale on your plant.

Black sooty mold on an Azalea
Black Sooty Mold on an Azalea

How to Treat Aphids and Scale

Inspect your plant for aphids every now and then by looking under the leaves where they love to hide. Black sooty spots on your lower limbs is a sure sign of their presence. If caught early, you can blast them off with a water hose but they will most surely come back.

Treating your plant with Neem oil is the best way to do this. You can find neem oil or a product containing it in just about any garden center.

Follow the directions on your product with the mixture. Once you have it mixed correctly in your garden sprayer, you want to dowse the whole area until the plant is dripping. It won’t hurt the plant. Most of the time it will also only hurt leaf eating or bark chewing insects. But to be safe, try to avoid the flowers of the plant so as to not kill pollinators.

Black sooty mold on a crepe myrtle
Black Sooty Mold on Crepe Myrtle

How Neem Oil Works

The neem oil disrupts the hormones of the insects preventing them from molting and growing through their various stages. It also disrupts their ability to lay eggs, therefore reproducing. I have also read that it messes with their digestion, so they are sucking less on your plants.

Keep it mind it takes time, but only a few days depending on the size of the infestation.

Where does Neem Oil come from?

Neem oil comes from …you guessed it—the Neem Tree!

It is created from crushing the seeds and extracting the oil much like Olive oil or any oil is made.

Neem Oil can be harmful if consumed in large amounts or it could irritate certain people’s skin. So just read your products directions carefully, and wear gloves if you think there’s a risk.

You need to get the population under control before moving on, or it will just come back. Once you have the Aphids or Scale under control, you’ll need to clean off the sooty mold that’s already there.

How to Remove Black Sooty Mold

This is done by mixing a mild soap and water solution and spraying your tree or shrub down. Kind of like cleaning a greasy pot. You spray it, let it sit a while and break down the sticky mold then rinse it off with a hose. If it’s bad, you may have to use a soft brush to scrape away the sooty mold.

If the infestation is really bad, you may have to remove some overly covered limbs or leaves. Crepe Myrtles being deciduous, you can wait till the winter to treat them as all the leaves will fall off and you will only have the limbs to clean.


Stay ahead of this aggravating situation by catching any sight of black sooty mold EARLY as possible. It’s relatively easy to treat but can be a huge hassle if left to spread. It can also lead to the loss of a prized tree or shrub in your landscape!

This Post Has 10 Comments

  1. Amy

    I buy a bag of worm castings at my nursery. I dump about half of a bag at the base of the plant. It will take a few months, but the aphids won’t bother your tree or shrub. I do this2-3 times a year. Definitely before leaves return

    1. ErickDStyron

      I have got to try this!. i have a Twilight crepe myrtle that is loaded right now with aphids, i let it go too long

  2. Faye D. Swilling

    Should I treat the mold now or wait until spring? Some of the leaves are falling off. We are due cold weather this weekend.

    1. ErickDStyron

      I would treat it now because the aphids and scale will overwinter on your plant, and continue to damage, weaken and even kill some plants

  3. Faye D. Swilling

    What do I need to do to get your newsletter by e-mail ?

    1. ErickDStyron

      I will try and set that back up on my home page. I have a Facebook page and a YouTube channel by the same name if you’d like to check them out

  4. Faye D. Swilling


  5. Yvonne Billiot

    Is Neem oil harmful to monarch cats?

    1. ErickDStyron

      yes it will totally kill them. I’ve read you can wash it off after treatment but don’t trust that on milk weed

  6. Yvonne H Billiot

    Thank you

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