Crape Myrtles are easy to grow and don’t usually require much special care and attention. So, when there’s a problem with your tree, it can be especially stressful. If you notice black sooty mold on your Crape Myrtle’s foliage, you’ll want to get it under control as quickly as possible.
Black sooty mold may appear on your Crape Myrtle’s foliage during the growing season. It’s an unsightly condition but is largely harmless to your plant’s overall health. This black mold typically indicates a pest problem, usually aphids, scale insects, mealybugs, or whiteflies.
So, before you go full-on panic mode and start cutting away healthy growth, let’s discuss exactly what black sooty mold is, what causes it, and how to get rid of it.
What is Black Sooty Mold?
Black sooty mold is a fairly common problem for Crape Myrtles. So, if you’re wondering what’s causing your Crape Myrtle’s leaves to turn black, you likely have sooty mold. Despite the unsightly appearance, this condition isn’t a severe disease or anything you need to panic about.
Black sooty mold is really a symptom of another problem — a pest infestation. This ugly black coating on your Crape Myrtle’s leaves and stems is a common mold that grows on honeydew. Honeydew is the sugary substance left behind when sap-sucking insects like aphids and scale insects feed on your plant.
So, while the black coating on your Crape Myrtle’s foliage may give you anxiety about its appearance, you don’t need to worry about it killing the plant or keeping it from blooming. Still, insect problems can lead to other issues, so you’ll want to take action sooner rather than later so that it doesn’t get out of hand.
What Causes Black Sooty Mold?
Black sooty mold is a secondary problem caused by the presence of certain insects. Some bugs like aphids, scale insects, mealybugs, and whiteflies feed on plants by inserting their mouthparts into the leaves and foliage to suck out the liquids inside.
As the insects feed, they excrete a sticky, sugary substance called honeydew. The honeydew coats leaves and stems, at first causing a shiny or sticky layer to build up. Over time, the honeydew becomes a food source for certain fungi, including the type which causes sooty mold.
Small amounts of honeydew typically don’t cause problems, and you may not even notice it. However, when a pest infestation becomes too severe, you may see black growth starting to coat your leaves and stems; this black “stuff” is the sooty mold. Other indicators that you’re dealing with black sooty mold include the presence of ants crawling up the side of the Crape Myrtle, as well as wasps or flies, which are all attracted to the sweet and sugary honeydew secretions.
Black sooty mold is most often caused by aphids, especially Crape Myrtle aphids. These common pests reproduce at exponential rates, meaning an infestation can quickly get out of control. If you have black sooty mold, you probably have an aphid problem. Bark scale insects also leave behind quite a bit of honeydew while feeding, meaning they can also contribute to the development of black sooty mold. Still, aphids are the most common problem with Crape Myrtles.
How to Treat Black Sooty Mold
Black sooty mold won’t kill your Crape Myrtle, but you may still want to get rid of it because of how much it affects your tree’s natural beauty. The good news is that you have many treatment options for dealing with black sooty mold.
First and foremost, you need to get the pest problem under control. Even if you treat and remove the black sooty mold, you won’t get rid of it for good without dealing with the underlying issue. Luckily, we’ve dedicated an entire article to treating your Crape Myrtles and controlling pests, which you can read here.
Start with removing any visible aphids from your Crape Myrtle using a stream of water. It’s the quickest and easiest way to knock those little buggers off without going to a lot of trouble. Then, you can treat the sooty mold by simply washing it off. Again, this isn’t a necessary step because the mold alone won’t harm your plant’s health, but it’s an option for improving your Crape’s appearance.
To remove black sooty mold, mix 4 ounces of dish soap with a gallon of water and apply it to the affected areas. Wait three or four minutes, then rinse the soapy solution off the plant. Keep in mind you don’t want to do this during the hottest part of the day to avoid the soap drying onto the foliage and burning the leaves. Also, this might not be an option if your Crape Myrtle is very large.
Another option is horticultural oil or Neem oil. These products will kill aphids on contact. Once the aphid population is reduced, the black sooty mold should clear up on its own in time as the old growth drops off and new growth comes in. Remember, horticultural oils should be applied in the evening and only when temperatures are below ninety degrees.
For severe infestations, you may need to use something a little more substantial. You can use either a topical application of an acephate product or a soil drench through the root system. The topical application is good to use during the growing season, while the soil drench is good to use at the beginning of the season.
The soil drench will last for the entire growing season, so it’s best to apply it early if you want to go that route. These chemical options are great for severe or persistent infestations, but it’s always best to try natural options first and then move on to chemical options as a last resort.
Natural Options for Getting Rid of Black Sooty Mold
Getting rid of black sooty mold starts with getting rid of the insects causing the problem in the first place. In most cases, that means dealing with Crape Myrtle aphids or bark scale insects. In addition to horticultural oil and Neem oil, other natural options include letting beneficial insects do the work for you.
The best way to reduce the aphid population is by encouraging their natural predators, like ladybugs, to inhabit your garden. Encourage these beneficial insects by avoiding unnecessary pesticides, providing a water source, and keeping your plants healthy.
Another option is to plant aphid-resistant varieties. There are Crape Myrtle hybrids with moderate aphid resistance, like Muskogee, Natchez, Tuskegee, Hopi, and many others.
How to Keep Your Tree Healthy in the Future
The best defense against black sooty mold is a good offense, which means working to keep your Crape Myrtle healthy and less susceptible to pest damage and other diseases. Remember, black sooty mold is more of a symptom than a problem. Its presence indicates that you may be dealing with an aphid or other pest infestation, so you’ll have to address that issue first.
Keeping your tree healthy starts with proper planning. Be sure to plant your Crape Myrtle in the right location where it will get plenty of sunshine and won’t outgrow its space. Airflow is important for preventing molds and fungi from taking hold on your tree, so proper pruning is also a must. To read more about pruning your Crape, check out this article.
Putting It All Together
If your Crape Myrtle develops an unsightly condition, it can be very distressing. Black sooty mold is one of those unfortunate afflictions that can impact your tree’s everyday summer beauty, but rest assured that it won’t kill your Crape. Even so, unsightly black leaves are not what you want to see on your Crape Myrtle.
Just remember that sooty mold is a byproduct of pest activity. Aphids and scale insects are the most likely culprits, as they leave behind a sticky coating where molds can thrive. Prevent and treat black sooty mold by dealing with the pest problem first.
Your best defense against honeydew-producing pests and black sooty mold are natural predators like ladybugs, green lacewings, parasitic wasps, and other beneficial insects. Encourage the presence of these natural pest controllers in your landscape as much as possible, and you’ll have fewer unwanted visitors to deal with each summer.