By Matt Gibson
If you have a plant, shrub, or tree that looks like it has spent a little bit too much time next to a fireplace, its leaves and branches covered with a thick layer of black soot like the face of a chimney sweeper after a double shift, there’s a good chance that your plant is suffering from a fungal condition known as sooty mold fungus. Though the fungus does little actual harm to the plant it infects, it is certainly unsightly and an unwanted presence in any garden. Thankfully, it is relatively easy to treat and remove.
About Sooty Mold Fungus
Sooty mold appears on plants and any objects or structures in the near vicinity of affected plants as a dark gray to black soot-like powdery coating that forms on the outer layer of plants, specifically on the branches, leaves, fruit, and anything else in the general area of the plant or plants in question. Sooty mold forms when fungal spores from ascomycete, capnodium and saprophytic fungi land on plants that are coated in a sugary, sticky substance that is excreted by common garden pests like aphids [https://www.gardeningchannel.com/all-about-aphid-control/], mealybugs, white flies, and scale. The fungal spores stick to the honeydew left behind by these parasites, and sooty mold grows on the honeydew itself.
Though sooty mold doesn’t grow directly on the plants, that doesn’t mean that affected plants do not suffer from the growth of the fungus as it can quickly cover every branch and leaf on the entire plant with a thick, black, sooty layer. The growth doesn’t hurt the plant directly, but the dark layer of sooty mold decreases photosynthesis, blocking the sun’s rays from the leaves, which subsequently start to wilt, wither, and eventually die if the growth isn’t treated.
Sooty mold is occasionally spotted as a minor condition, on plants in which only a few leaves were coated in honeydew, and eventually, in the moldy growth. In these cases, damage is very limited, and also very easily eradicated. The cause of the fungus, as well as the severity of the issue, strangely, is not the fungi itself, but the honeydew, and, even more so, the insects that secrete it. The size of the pest infestation determines the amount of honeydew on the foliage of the affected plant or plants. The amount of honeydew present determines the severity of the soot-like mold that coats the leaves and fruit of the affected plant.
Identification and Symptoms of Sooty Mold Fungus
Identifying sooty mold fungus is fairly easy. If you notice a dark gray to black sooty coating on the foliage and fruit of a plant, shrub, or tree, chances are, sooty mold fungus is the culprit. If you notice the presence of honeydew on the leaves, branches, and twigs of one of your plants, you may have time to keep the fungus from forming. If you notice the presence of aphids, mealy bugs, or other tiny insects on your plant, you might even be able to prevent the spread of honeydew by treating the plant for pests before they have a chance to coat the leaves with their sugary-sweet substance.
The symptoms of sooty black mold are simple and easy to see. The affected plants become covered in a sooty layer of gray or black grime. The mold is powdery and sticky and the layer is relatively thick. The dark color and the thickness of the fungal growth blocks photosynthesis, which keeps the chlorophyll from functioning properly, which can eventually cause the leaves to wither and die. Though the leaves of affected plants are sometimes casualties of sooty mold fungus, the plants, shrubs, and trees live on long after the fungal growth has come and gone. Soot can be removed, leaves can be regrown, and plants that have been the victims of major infestations can make miraculous recoveries with proper treatment.
Treatment and Control Options For Sooty Mold Fungus
Prevention techniques for avoiding issues with sooty mold are hard to find because when the issue first starts to develop, it is not entirely recognizable. However, there are a couple of ways that gardeners can reduce the likelihood of sooty mold infections in the garden. One way to lower the chances of developing sooty mold problems is to raise healthy garden plants.
Healthy, happy plants are less likely to attract pests that produce honeydew. Keeping your plants properly hydrated and well fed can go a long way towards preventing sooty mold and many other pest and disease problems. If your plants become weakened by insufficient nutrients available in the soil, or by dehydration, they are more vulnerable to attack from pests and parasites.
Another key to preventing pest and disease issues in your garden is to develop a diverse plant population in your garden beds and to practice regular crop rotation. The best way to protect plants from their natural enemies is to surround them with a large variety of different plants. Practicing crop rotation keeps pests from being able to discern where susceptible crops are going to be planted next. Certain plants deter specific predators, while others are resistant to particular diseases. Creating a diverse group makes it harder for pests and diseases to locate weak plants and establish a presence in the soil, and rotating where you plant your crops each year makes it much tougher for pests and soil-borne diseases to follow your plants around.
Treatment & Control
Treating sooty mold fungus is relatively easy, as long as you are willing to follow the steps required to eliminate the cause of the fungus first, then remove the fungus from the plant entirely. Once the pest issue has been treated, the soot-like mold needs to be removed entirely. The removal process can take more than one treatment to get rid of all traces of the mold. Follow this easy step-by-step process that first focuses on ridding your plants of sucking insects which produce honeydew, and then on removing all traces of sooty mold from the plant.
Step One – The first step in dealing with sooty mold fungus is to destroy the pests that cause the fungal disease. Light infestations can be knocked off of the plant with a strong burst of water from a pressurized water hose. However, large infestations of sucking insects such as aphids, mealybugs, whiteflies, and scale will need to be treated with a horticultural oil spray to effectively rid the plant of their presence.
Using a one gallon pump sprayer, make a horticultural oil solution spray to spray down your plants with. For aphids and white flies, create a solution spray by mixing four tablespoons of neem oil or a paraffin-based horticultural oil with one gallon of water. For mealybugs and scale, mix four tablespoons of a basic horticultural oil, or a fish-based oil with one gallon of water. Shake the mixture hard and well to fully incorporate the oil into the gallon of water and discourage separation, then spray down the affected plant or plants when they are dry until all affected areas are fully soaked. The best time to spray your plants is early in the morning or after sunset, so that they have plenty of time to dry before they are exposed to the intense heat of the afternoon sun.
Step Two (If necessary) – For severe infestations, you may notice that there are still some pests on the plants six or seven days after the first application. As long as the plant is not having a tough time recovering from the initial treatment, reapply the diluted horticultural oil spray again following the same instructions outlined in the previous step. Light infestations usually only need one treatment, but more severe pest and sooty mold problems may require a second application.
Step Three – Two days after the final horticultural oil drenching, it is time to start dealing with the mold. Early in the morning, using a pressurized garden hose sprayer attachment set to jet, or full, spray down the affected plants with a forceful blast of water to remove sooty mold, focusing on removing as much mold from the surface of the leaves as possible. Spraying the affected plants early in the day will ensure that they have plenty of time to dry before the blazing afternoon heat rolls in. If plants are not fully dry and temperatures rise over 100 degrees F, the areas of the foliage that are wet will burn.
Step Four – Though a good high-pressured spraying of the foliage will often remove the majority of sooty mold fungus from the plant, there is often quite a bit of soot still remaining on the leaves and lower branches of affected plants after one round of high-pressure spraying. To encourage the complete removal of all fungal residue, add a little bit of soap to the water and spray the affected plants down again in order to get the rest of the soot-like grime off of the affected plant.
Clean the pump sprayer thoroughly to remove any residue of horticultural oil from the tool before making a new solution. To make your own soapy mold remover spray, just mix one teaspoon of a mild liquid soap or detergent with a gallon of water and mix thoroughly. Spray the plant down until all affected leaves are well coated with the soapy mixture and the leaves are dripping off excess soapy water. The diluted soap mixture will help break down and eliminate any leftover sooty mold remnants.
Step Five – The next day after applying the soap water spray, use the pressurized hose attachment again, set to a strong burst setting like jet or full, to rinse off the soapy residue and any remaining sooty mold.
Step Six – Using a clean, sharp pair of garden shears, trim off any heavily mold damaged foliage and discard it immediately. Wipe down the shears after each cut that you make with a rag soaked in rubbing alcohol to kill off any fungal spores that may attempt to reinfect the plant if you trim the foliage with infected blades
Sooty mold fungus is not very pretty to look at, and once it has taken a hold on a plant or group of plants in your garden, you will have to undergo a thorough process of removal to rid the affected plant or plants of the disease. However, sooty mold fungus is not a death sentence for plants or the gardeners who love and care for them. Plants affected by the disease are usually able to make a full recovery if treated and rarely die even when left untreated. Sooty mold fungus is somewhat tough to remove and practically impossible to prevent, but it is nothing to fear, especially now that you know how to treat it effectively.
Frequently Asked Questions About Sooty Mold Fungus
Can sooty mold kill plants?
Sooty mold covers plant tissue, often coating entire leaves with a dark grey to black soot-like mold. Though sooty mold infections are not typically lethal and appear to be a lot more severe than they are in reality, the mold layer does block the sun from the plant’s foliage, which decreases the photosynthesis processes within the plant and significantly weakens it. Though sooty mold fungal infections aren’t typically lethal, they are caused by sucking insects which can kill the plant if left untreated.
Does Dawn dish soap kill mold?
Dish soap, on its own, cannot kill mold, though it is one of several ingredients that you can put to use to make a bleach solution that works to kill and remove mold. Dish soap, like Dawn, or other brands, can be added to a bleach solution to help the solution break through the surface and remove mold from porous materials like grout. To make a mold killing bleach solution using the penetrating power of dish soap, mix one cup of bleach with one gallon of water, blend together well, then add a small amount of dish soap.
Does sooty mold spread?
Sooty mold is a fungal disease that can spread to any area of an infected plant that is coated with honeydew. Honeydew is the sweet, sticky substance that is secreted onto plants from small, sucking insects such as aphids, whiteflies, scale, and mealybugs. Large infestations of these pests can lead to plants covered in honeydew. Sooty mold fungal spores adhere to the leaves of infected plants by sticking to the honeydew on the surface of the foliage. Sooty mold fungus then quickly spreads to all of the areas of the plant where honeydew is present.
To kill and remove sooty mold fungus from affected plants, destroying the pests responsible for the infection is first and foremost. After the pest infestation is contained and destroyed, sooty mold can then be removed from the affected plants. If sooty mold removal was successful, the plant should remain free of any signs of the fungus. Sooty mold cannot spread without the presence of honeydew, so if the mold starts to come back, that means that the pests that caused the fungus are still present.
How do you remove sooty mold from citrus trees?
Removing sooty mold from citrus trees involves the same general process as removing sooty mold from any other type of plant. The first step is to eradicate the honeydew-making pests that caused the fungus in the first place. Once the pests have been knocked off the plant with a burst of water or destroyed with a horticultural oil treatment, you can begin to remove sooty mold from the surface of the plant’s leaves, fruit, and branches.
To remove sooty mold from affected plants, shrubs, or trees, the surface area of the plant must be cleaned thoroughly using strong blasts of water sprayed directly on the plant using a high-pressure garden hose attachment. After spraying down the affected plant with blasts from the garden hose, a pump sprayer can be used to drench the foliage with soapy water to further break down the mold and loosen it up enough so that it can be removed with yet another round of water blasts.
Alternatively, the surface area of the affected plants can be cleaned by hand using a washcloth or a sponge. Sooty mold on the surface of higher leaves and branches that are too high to clean by hand can be removed using a high-pressure spray to blast away the soot-like growth. Sooty mold removal is not a simple task, and sometimes treatments have to be repeated multiple times before the unsightly fungal growth is completely removed.
How do you treat sooty mold?
Treating sooty mold on garden plants, shrubs, and trees involves several important steps. Before you can focus your efforts on removing the mold, the affected plants need to be treated to destroy the pests that cause sooty mold in the first place. If aphids, mealybugs, whiteflies, or scale insects are still present on the affected plant, sooty mold removal is basically a waste of time and effort, as the insects will re-apply their sticky honeydew secretions, which will eventually attract sooty mold fungal spores, and the mold will come back in full force. So, the first step to treating sooty mold is to elimiate the pest infestation that caused the mold in the first place.
Small pest infestations are easy to treat. A thorough blast of water from a high-pressure garden hose will knock off the majority of the colony. A second blast a few hours later should finish off the job. Large pest infestations, however, do not have a quick and easy fix. When you have an abundance of tiny sucking insects, the best treatment is to make a diluted horticultural oil spray.
For scale and mealybug infestations, put four tablespoons of a standard horticultural oil or a fish-based oil into one gallon of water and mix together well. Put the solution into a pump sprayer and treat each infested plant by spraying it until every affected area is drenched. For aphids and whiteflies, use a neem-oil or a paraffin-based oil instead of a standard or fish-based oil, and follow the same directions, soaking plants suffering from insect infestations until every problem area is dripping.
Do not spray your plants down with horticultural oils during the afternoon, when the sun is blazing hot, or the foliage will burn as the sun heats up the liquid on the foliage. Instead, treat your plants early in the morning or just after sunset so that the leaves will have a chance to dry off before the sun heats up. Moderate-sized infestations typically only require one treatment of a horticultural solution, wfhile larger infestations may require two applications. Check your plants three to five days following the initial treatment. If you still notice the presence of pests after the fifth day, soak your plants in the solution again.
After the pests have been eliminated, it is time to shift focus to the mold. To handle the sooty mold, first hit the affected plants with another blast of water from the garden hose. This will begin to loosen up the sooty mold that is coating the leaves, branches, and twigs of the infected plant. Next, using a pump sprayer, make a solution by diluting a teaspoon of liquid soap or detergent in a gallon of water and spray it all over the sooty plants to help break down the sticky substances coating the plant so that they can be removed more easily. The day after soaking the plants in the soapy solution, give them another blast of water to remove the remaining mold and soap residues.
Finally, look over the plant carefully for any remaining signs of mold. Leaves that were heavily damaged by the mold should be clipped off with a clean pair of gardening shears. Wipe down the shears with an alcohol soaked cloth between clippings to kill any active fungi spores that may have attached themselves to the blade. If there are any places on the plant where you notice that there is still mold residue, use a wet cloth or a sponge to clean off the areas, or cut them off the plant completely.
Is sooty mold harmful to humans?
No, sooty mold is not believed to be harmful to humans. Black molds are often believed to be harmful to humans, but sooty mold is not at all toxic to people.
What causes sooty mold?
Sooty mold is caused by pest infestations of small sucking insects with piercing mouths, including aphids, whiteflies, mealybugs, and scale. The insects secrete a sweet, sticky substance called honeydew, which coats the leaves and stems, or branches of certain plants. The honeydew coating attracts fungal spores, which adhere to the honeydew. Once a few sooty mold fungal spores are present, the fungus quickly spreads and affects the whole plant, making it appear as if it is covered in grime and soot.
What insects cause sooty mold?
A group or four small, flying, piercing-mouthed, sucking insects create honeydew and are responsible for causing the formation of sooty mold. The insects that cause sooty mold to form are whiteflies, scale, aphids, and mealybugs.
What is a natural way to get rid of sooty mold?
Get rid of sooty mold naturally by knocking off the pests with a direct blast of high-pressured water. Once the pests are gone, treat sooty mold by cleaning the leaves with a high-pressure hose and by hand, using a wet cloth or a sponge to remove mold residue.
What plants are affected by sooty mold?
There is a large number of flowering plants, shrubs, and trees which are affected by sooty mold fungus. Fruit trees, such as pear, apple, fig, and olive, citrus trees, such as grapefruit, orange, lemon, and bergamot, Veggie plants,like tomatoes, flowers, such as hydrangeas, azaleas, camellias, rhododendrons, ornamental shrubs like rose bushes, laurel, and oleander, as well as trees like catalpa, elm, pine, linden, maple, hibiscus crepe myrtle, and black walnut .