“How did my plants get so dirty?”

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As it’s name implies, sooty mold is easy to identify by its “sooty” appearance.

Photo Credit: ©Buglady Consulting

The real question is, are you looking at dust, dirt and grime, or are your plants showing signs of fungal growth? No matter where you live or what kind of plant you have, sooty mold may be the cause of unsightly black residue on the plants in your home or landscape.

Sooty mold is a dull-black fungus that can grow on the leaves, fruit and stems of indoor and outdoor plants. The fungus is easy to identify by its “sooty” appearance. Light infestations may begin at the base of leaves and move toward the tips. Heavy infestations can cause the entire plant to appear black.

Sooty mold is caused by the presence of aphids, mealybugs, scale and whiteflies. These insect pests have mouthparts that suck plant juices, and as waste, they secrete a sweet substance known as honeydew. The honeydew lays on plant surfaces and over time grows into this specific mold.

Since almost all plants are susceptible to aphids, mealybugs and whiteflies, it stands to reason that almost all plants are susceptible to sooty mold. Crapemyrtles, hollies and azaleas are just a few of the numerous landscape plants that you may find covered with the fungus. You’re most likely to find sooty mold in the landscape in spring and summer, when insects are the most active.

On houseplants, sooty mold can be present and active any time of year. You’ll often find it on your houseplant before you spot the insect problem. (If you see sooty mold on a Ficus or other woody-stemmed houseplant and you don’t see any obvious insects, look along the stems, and you’re likely to find armored scale insects camouflaged there.)

Although the insects that cause sooty mold can cause severe damage to the plant, sooty mold itself is relatively harmless. Because the fungus covers the leaf surface, plants can’t manufacture food for themselves as quickly, so plant growth will slow down. But luckily no lasting effects remain after sooty mold is controlled.

Controlling sooty mold is as simple as controlling the insect creating the honeydew. Contrary to what you may think, applying a fungicide is not necessary and won’t aid in the control of sooty mold. Instead, find the insect causing the problem and research the best control method for that specific insect.

After the insect is suppressed, the sooty black appearance may remain on the plant for the remainder of the season. For landscape plants, there’s little you can do to remove the “soot” on a large scale, but as long as the insect is controlled, the unsightly appearance will disappear over time. For houseplants, the leaves can be wiped down with a cloth and mild soapy water – but make sure the soap residue is thoroughly rinsed off. (To rinse, you can simply place the plant in the shower, or take larger plants outside on a warm day and hose off any residue.)

The good news is that sooty mold is a plant disease with a happy ending: It’s easy to identify, easy to control and does little harm to a plant.