Black Sooty Mold: The Real Reason You Don’t Want It On Your Trees

Unaffected foliage vs affected foliage, spotted locally on a Holly tree by one of our Certified Arborists

Have you ever encountered annoying sticky sap coating your car, furniture, or walkway? Did you find it under a tree? Say hello to honeydew.

Honeydew is a common plant health issue. It’s gross, it’s annoying, and it can be difficult to remove. But here’s the worst part of all: it attracts pests that can become detrimental to plants and can lead to the development of sooty mold.

In this article, we talk all about sooty mold, the unsightly consequences it leaves on your landscape, and what it really means when you find it on your trees.

What is Sooty Mold?

Sooty mold and azalea bark scale found on stems of crepe myrtle trees; spotted by one of our Certified Arborists
Sooty mold and azalea bark scale found on stems of crepe myrtle trees; spotted by one of our Certified Arborists

Sooty mold is a type of plant mold that results in an unsightly black discoloration on trees. Without proper control, it can make the host plant turn entirely black.

This tree mold grows on the honeydew residue left by sucking insects, such as aphids and soft scales, that infest the plant. These pests can cause the host plant to lose its ability to absorb enough sunlight. Consequently, the affected plant risks not producing the nutrients it needs to survive.

With that said, can you guess what the real cause of concern is when it comes to sooty mold? That’s right – it isn’t the mold itself, but rather its indication that pests are infesting your landscape. If left untreated, these sap sucking insects will leave a detrimental aftermath on your plants.

Therefore, to save your tree, it’s best to act proactively; and, if your tree has already been affected, you’ll need to act immediately.

What insects cause black sooty mold?

  • Lace bugs (targets: Azaleas, Rhododendrons, and other plants in the heath family)
  • Scale insects (targets: Azaleas, Rhododendron, Huckleberry, Andromeda, Hawthorn, Poplar, Maple, Oak, Linden, Birch, & Willow)
  • Aphids (targets: Ash, Crape Myrtles, Fir, Pine, Spruce, Cedar, Hackberry, Roses, and Tulip Poplars)

>> Read here to learn more about these tree bugs

Sooty Mold Symptoms

Along with the obvious black discoloration, there are a few other symptoms you can look out for when trying to identify if your trees are dealing with sooty mold.

Symptoms include:

  • Stunted plant growth
  • Early leaf drop
  • Tree bugs sucking up sap
  • Honeydew residue

If you spot these symptoms in your plants, it’s important to reserve an appointment with your Certified Arborist to prevent further damage on your landscape.

Sooty Mold Treatment

Black sooty mold found on walkway patio outside home
Black sooty mold on walkway outside home, spotted by one of our Certified Arborists

Here’s the thing – when you spot sooty mold on your tree, the damage is already happening in your landscape. And that unsightly black mold? It isn’t coming off. The best way to act against it is to act proactively.

How to prevent sooty mold: Gain control against the insects that can overwinter on the host plant. A simple solution to this is having a preventative dormant oil spray applied to your plants.

By having the treatment applied before spring, you can prevent overwintering insects from wrecking havoc on your landscape. (And, in case you missed it, spring is right around the corner!)

Already see signs of the mold? Don’t worry – we can still treat the causal agent! With help from our tree experts, you can suppress the infestation and improve your plants’ health over time.

**Here’s a tip from one of our Certified Arborists: Do NOT power wash your affected plants, as it can actually do more damage to them.

We get it, the plant mold can ruin a great landscape. If you want, you can power wash the mold off the tree’s nearby environment (walkways, sidewalks, driveways, patios, etc.), but do be careful walking as it can make surfaces become slippery.


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