Sooty mold on leaves

The Plant Doctor – Sooty Mold

Sooty Mold
Most common seasons
spring, summer, fall
Any, but gets
worse during
fair to hot weather.

Affected plants
and materials
Any outdoor structure;
many plants but
especially gardenias,
camellias, laurels,
azaleas, and crepe

Sooty mold is a frequent problem on the leaves of many evergreen shrubs including azaleas, camellias, laurels, and gardenias. It can also be a problem on deciduous trees and shrubs including crepe myrtles, Chinese elms, hollies, silver maples, or sugarberries, or on plants growing beneath any of these plants. You may also see the black “sooty mold” on walls, sidewalks, fences, automobiles, or almost anything else that has dropped from plants above them.

Quick Symptoms
Sooty mold is usually a black powdery coating that develops on leaves and twigs. Sometimes the black layer may be hard and stick tightly to the leaf. During spring rains, the black layer may flake off or peel away from part of the leaf, leaving healthy looking green areas with splotches of the black sooty mold (Figure 1).

The Fungi and the Harm It Causes
There are several fungi or molds that cause this problem, but they all grow in a sugar or honeydew layer that has been deposited by insects (Figure 2). If you solve the insect problem, the sugar deposits will stop, and the sooty mold will slowly go away.

Fungi that cause sooty mold do not attack plants directly, but obtain their nutrients from the honeydew itself. Although the fungi do not feed on the plants, they can indirectly destroy the beauty of the plant and, if the concentration of the mold is heavy enough, shade out enough light to yellow and stunt the plant. In severe cases, the plant or plant parts may die, but this is probably due to damage caused by the insects.

The fungi spread from one plant to another by water-splashed spores and hyphal fragments, and by air-borne spores.

Some insects such as aphids, soft scales, and white flies eat by sucking plant sap. Plant sap is rich in sugar but not as rich in other items the insect requires in its diet. This means the insects are eating excess sugar, and they have to get rid of it. When they do this, the honeydew falls on the plant or onto plants or structures below the host plant.

You can control sooty mold by controlling the insects that produce this sugar-like material. There are several insecticides or combinations of insecticides available to control these sucking insects. The insecticide used will depend upon the insect, the host plant, and any safety considerations. Insect identification and insecticide selection are discussed in Extension Publication 2369 Insect Pests of Perennial Plants in the Home Landscape.

Once sooty mold is established, it is not easy to remove. The best method to remove the mold is to soak affected plants in a water and detergent mixture. Use 1 tablespoon of household liquid detergent per gallon of water and spray it on the plants. Wait 15 minutes, then wash the detergent solution off with a strong stream of water. You may have to repeat this treatment a number of times over a few weeks. Generally speaking, the mold will gradually dry and flake off once the insects are under control. The mildew will continue to age over the winter, and most will flake off during the early spring (Figure 1).

Figure 1. Sooty mold on holly in the early spring. Notice the flaking from the leaf.Figure 2. Vigorously growing sooty mold on holly. Note the sooty mold fungi are producing stalks (conidiophores) to launch their spores into the air.

The information given here is for educational purposes only. References to commercial products, trade names, or suppliers are made with the understanding that no endorsement is implied and that no discrimination against other products or suppliers is intended.

Information Sheet 1938 (POD-07-18)

By Alan Henn, PhD, Extension Professor, Biochemistry, Molecular Biology, Entomology, and Plant Pathology.

Sooty Mold: An Unsightly Problem with A Simple Solution

In my backyard I have a small overlooked corner that has been untended for years. In this corner there is a hedge that up until very recently was covered in a dark black soot. It came as quite a shock to me to realize that the hedge was actually a plant (a podocarpus to be specific) and it was supposed to be GREEN! What can turn a perfectly healthy shrub into an unrecognizable cluster of twigs? Sooty Mold!

Sooty mold, as its name implies, is a dark soot like covering on the leaves and stems of a plant. This “mold” can be scraped off with a fingernail to reveal a healthy green leaf below. Sooty mold is actually a fungus that grows on plants with heavy aphid, scale or whitefly damage. When these pests munch on your plants they excrete a residue euphemistically called “honeydew”. Adorable, right? It is on this honeydew that the sooty mold takes up residence. If the infected plant is under a tree, then the pests may be in the tree above causing the honeydew to fall to the shrub below.

Controlling sooty mold is simple. First you need to address the root cause of the sooty mold: aphids, scale, and whiteflies. These critters are rather small and might not be easily visible. But if you have sooty mold it is a sure bet they are around. If the problem plant is under a tree, pest management may be out of reach. In these instances you can still treat the cosmetic problem by skipping to step 2.

Step 1: Pest Management

To treat your plant against these pest, spray the leaves with a solution of either horticultural oil or neem oil. Horticultural oil and neem oil are less toxic pesticides that will rid your plant of heavy infestations. Spray in the early evening after the plant is no longer in direct sunlight. Just like tanning oil, neem and horticultural oil can exaggerate the effects of the sun and you run the risk of sunburning the leaves if you apply in full sun. Depending on the severity of the infestation, repeat applications may need to be made every two weeks or so. Always follow the directions when using any pesticide.

Step 2: Soot Removal

You remove the soot in the same way you would remove greasy caked on goo in the kitchen, by letting it soak in dishwashing liquid. Use your sprayer and hose down the plant with a solution of dishwashing soap. This step does double-duty by cleaning up the sooty mold and killing some of the pests that cause sooty mold. Avoid using a degreaser or soap/detergent for an automatic washer. Let the soap stay on the plant for a while as it loosens up the soot. Next time it rains (or if you are impatient you can spray it down yourself) you will see much of the black coating simply washing away revealing healthy green leaves.

Step 3: Maintenance

Chances are that the problem did not come up overnight so be patient with the treatment. You can repeat these steps until you are satisfied with the appearance of your plant but don’t rush out to hit it with a pressure washer; your plant won’t thank you for that! By staying on top of the pest problem the sooty mold will not occur on new growth. Eventually you will have a beautiful, healthy and appropriately green plant once again!

Additional Resources:

Gardening in a Minute


Aphids on Landscape Plants


Sooty Mould

Sooty mould on citrus leaves

Sooty mould looks just like the name implies – like a layer of black or grey fireplace soot over the leaves and branches.

It might sound strange but sooty mould is actually a problem caused by sap sucking insects like aphids, scale, whitefly, mealybugs and mites. These insects exude a sugary substance called honeydew which the sooty mould grows off. Ants will also feed on the honeydew so it is common to see ants and sooty mould together on plants. Aside from being unsightly the sooty mould can block sunlight to leaves and reduce plant vigour in severe cases.

To get rid of the sooty mould you need to address the pest problem. Once you have that under control and they are no longer producing the honeydew, the sooty mould will dry up and flake off.

Plants Attacked
All plants can be affected by sooty mould.

Organic Control Methods for Sooty Mould

Sooty mould on fig leaves with scale along the middle

Identify what sap sucking insect is present and treat accordingly. If you can’t see any pests then there’s a pretty good chance of it being:

  • scale (some types are very good at camouflage) or,
  • mites (very small and difficult to spot with the naked eye).

eco-oil and eco-neem will both control a broad range of sap-sucking insects. Spray with either a couple of times to kill the pests. Ensure good coverage all over the plants so you don’t miss any of the pests.

Once the sooty mould starts to dry and flake hosing can help to remove the flaky bits faster.

There are also various predatory insects which eat sap sucking insects but they sometimes take time to get established and bring the pests under control. If your sooty mould is severe then get on top of it quickly by spraying with eco-oil or eco-neem first. You can learn more about beneficial insects in The Garden Guardians book. We also sell a range of live predatory insects called the Backyard Buddies.

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Tuesday – January 04, 2011

From: Lewisburg, PA
Region: Mid-Atlantic
Topic: Diseases and Disorders, Pests, Trees
Title: White fuzz on Christmas tree from Lewisburg PA
Answered by: Barbara Medford


Our Canaan fir Christmas tree is now coated with white fuzz after being up for 4 weeks. The fuzz looks like spider webs, but it is also in clumps around the needles. When you rub your finger on it, it seems chalky. Any idea of what this is?


Since we had not heard of a Canaan fir, we found this article from the National Christmas Tree Association on the Canaan Fir. In our Native Plant Database, we found information on our webpage on Abies balsamea (Balsam fir). On that page (which see), we found this information on pests and diseases of this plant:

“Conditions Comments: This slow-growing tree loses its lower branches as it matures, but maintains its dense, spire-like habit throughout its life. It needs to be kept cool and moist during the growing season. It is troubled by spruce budworm, woolly aphid and several canker diseases and is heavily browsed by deer. It is very resistant to attack by gypsy moth. The soft foliage makes balsam a favorite Christmas tree.”

Any of these conditions might be the cause of the fuzz on the tree, but not likely. It is, first of all, a dead tree. Second, those various insects are no doubt hiding somewhere as eggs or larvae and not likely to be active. Our best guess is that it is some kind of mold, possibly because you have had the tree in a water reservoir.

Our advice? Again, it’s a dead tree, and Christmas is well over. Many communities have tree-recycling programs, so that the organic matter in the tree can be put to good use. Whatever is on your tree branches, you don’t want it in the house. Throw it out.

Images of Abies balsamea var. phanerolepsis from Google.

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How To Get Rid Of Sooty Mold

If your plant has started to look like it has been spending time sitting next to a fire and is now covered in a black soot, chances are, your plant is suffering from sooty mold. How to get rid of sooty mold can be a perplexing question as it may seem that it appears out of nowhere, but it is a fixable problem.

What is Sooty Mold?

Sooty mold is a type of plant mold. It is a type of mold that growing in the honeydew or secretion of many common plant pests, such as aphids or scale. The pests cover the leaves of your plant in honeydew and the sooty mold spore lands on the honeydew and begins to reproduce.

Symptoms of Sooty Plant Mold Growth

Sooty mold looks a lot like the name implies. Your plant’s twigs, branches or leaves will be covered in a grimy, black soot. Many people believe that someone may have dumped ashes or may have even caught the plant on fire when they first see this plant mold.

Most plants affected by this plant mold growth will also have some sort of pest problem. Some plants, like gardenias and roses, which are prone to pest problems, will be more susceptible to this plant mold growth.

How to Get Rid of Sooty Mold

Treating plant mold like sooty mold is best done by treating the source of the problem. This would be the pests that excrete the honeydew the mold needs to live.

First, determine which pest you have and then eliminate it from your plant. Once the pest problem has been solved, the sooty plant mold growth can be easily washed off the leaves, stems and branches.

Neem oil is an effective treatment for both the pest problem and fungus.

Will Sooty Mold Kill My Plant?

This plant mold growth is generally not lethal to plants, but the pests that it needs to grow can kill a plant. At the first sign of sooty mold, find the pest that is producing the honeydew and eliminate it.

I was recently asked to take a look at a friends dwarf Lemon tree, planted in pride of place right outside their lovely double glass doors in their dinning area.

There stood a small, sad looking tree that was pretty hard to spot as being a Lemon tree, because it was absolutely covered in a thick, black, sticky coating on all of it’s leaves.

Not being gardeners of any variety my friends were planning on pulling their Lemon tree out so they could replace it with something that didn’t look so sick, until I offered to help them figure out what was wrong with it.

As soon as I laid eyes on their poor little tree it was clear that it had fallen victim to a severe case of black sooty mould.

What Is Black Sooty Mould

Most common in citrus trees, black sooty mould is as it sounds. A horrible black, sooty like mould that coats the leaves and branches of a plant, making them appear to be rotten and very unwell.

Black sooty mould is actually multiple species of fungi that grow on the secretions made by insects, such as aphids or mealy bugs, who are doing the real damage by piercing the bark of the tree and sucking the sap, then secreting what is known as ‘honeydew’. A misnomer if I ever heard one.

So while black sooty mould might look like a life sentence for your tree, it’s actually not your main problem. It’s more of a sign that your tree has been invaded by insects that are eating at the tree and slowly killing it.

That’s not to say that the black mould is totally innocuous. It can also block out sunlight from the leaves, affecting the plants growth and it certainly makes the tree look horrible and unhealthy.

How To Get Rid Of Black Sooty Mold

The first main task in dealing with the mould is to get rid of the insects that are creating the sap secretions.

Use a horticultural pest clean oil such as Neem oil and spray the foliage of the plant to kill off all the insects that have made your plant their new home.

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Once all of the insects are removed from the tree you can begin to clean off the sooty mould.

Use a small amount of natural detergent to make a spray and coat all parts of the plant covered in the black mould. Make sure to get both sides of the leaves and let the detergent spray soak the leaves.

You can then either wait for the next good dose of rain to fall to wash the detergent off, or give your tree a good wash down with clean, clear water from the hose and you will see the black soot washing away.

You may need to do this step more than once if the mould cover was heavy. Don’t be tempted to scrub the leave or go overboard on the detergent spray for risk of doing more damage than the mould was in the first place.

If after ‘washing’ your tree you find that any of the branches have sustained too much damage due to the infestation, trim back the parts of the tree that are most affected, making sure to not prune your tree too hard, especially if it is a smaller decorative tree.

Once you have your plant looking more like it’s old, healthy self, make sure you keep on top of the insect control and continue to gently remove any of the sooty mould that remains until you have a display of green, shiny leaves once again.

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Topics #aphids #black soot mold #black soot mould #latest post #mealy bugs #pest #sooty mold #sooty mould

Usually my pest control efforts consist of taking the seed heads off invasive perennials, swatting flies, killing slugs and waiting for insect pests to disappear naturally. Plants very rarely die from insect infestation and a few holey leaves can be picked off or ignored. But I will take action if pest damage just beside my front door is particularly ugly.

Sooty mould on pieris.

The problem is a black coating which has appeared on the leaves of evergreen shrubs such as camellia, holly and pieris. This is a fungus called sooty mould which lives off the honeydew excreted by various sap-sucking insects living higher up. It can be softened by wiping with soapy tepid water, then rinsing off. The soot builds up on older leaves and stems, especially if there is no rain reaching the leaves, and requires annual cleaning unless the insect problem is dealt with.

The pestilential insects on these shrubs are often scales, looking like small, light brown bumps on the underside of the leaves. Most of the time the insect is shielded from insecticides by its shell-like scale, and is only vulnerable when it moves to new leaves in May or June. A good way to reduce insect populations is spraying or wiping both surfaces of the leaf with an insecticidal soap solution at this time. Horticultural oil can also be sprayed on, following the directions on the container, and as this acts by smothering the insect, the timing is not so vital.

Scale insect on pieris.

A more direct solution is to prune out and dispose of infested branches, and scrape off remaining scales if there are not too many of them. Sometimes one side of the shrub is infested first, so cut this away and pick off the remainder. Often a massive infestation occurs in a shrub which is planted in inhospitable conditions, such as under the eaves. Consider moving or removing it.

Check tall shrubs or those beneath overhanging aphid-infested trees regularly, and clean off the ugly sooty mould. A spray program to kill off the offending insects involves massive collateral damage to other insects, many of which help us by eating the bad guys and pollinating our fruit. If we kill the helpful insects, we have to take over the work they do.

– Sheila Watkins, Master Gardener

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