Back during the COVID era, I re-connected with an old friend who had a massive gardenia in her yard. (If you're reading -- hi, Corey!) She gave me a couple of clippings so I could try to propagate this beautiful and sweet-smelling plant at my house.
We have a perpetual deer problem in our yard, so I first planted the baby gardenia in a pot that I kept safe. Over time, with a little TLC, it grew into a size that I felt comfortable planting in the ground. I picked a spot outside a window where we'd be able to see and smell the gardenia when it bloomed. Fingers crossed!
To keep the deer at bay near its new home along the woodline, I painstakingly, well...staked...and netted around the growing plant. We have notoriously sandy soil in our yard, so I was cautiously optimistic. Much to my surprise, though, this gardenia totally flourished! It grew and grew -- until it didn't.
Recently, I noticed it had gotten really "leggy" with hardly any leaves near the bottom, and the leaves it did have were covered with a thick black substance. It looked terrible! This had happened to another gardenia I'd had in the backyard, which eventually lost all its leaves and stopped growing entirely. I was determined to save this one.
A Google search revealed that the gardenia was suffering from "sooty mold" and a horrible infestation of white flies.
Armed with my research, I started working to clean the soot off the leaves one by one. I used a wet paper towel with some gentle dish detergent, followed by a good spray with the hose. While elbow grease is admirable, you sometimes need a little help from a chemical or two, as well, so I also purchased a fungicide from a garden center and sprayed the entire thing down, clearing white fly larvae off the underside of the leaves as I went. I used GardenSafe brand Fungicide3.
I also planted a marigold at the base of the plant to ward off any new pests, since apparently they're repelled by these flowers.
Every few days, I'd go and give the plant a few good taps to knock off any additional white flies. I kept spritzing with the fungicide as directed. After awhile, I noticed lots of new green leaves sprouting on the lower branches and no sooty mold on them! It was also flaking off the older leaves. Before long, buds were forming within the clusters of healthy leaves. Success!
With a little research and a little TLC, I saved the gardenia from the Invasion of the White Flies, and I can't wait to enjoy all the bright white blooms to come.
In researching how to handle the situation, I came across this article below from our friend Bill Tyson at the UGA Extension Office. Read on for more on what to do if you have the same issue with this pesky plague on plants.
Sooty mold on plants is a sure sign of insect damage
By William G. Tyson
I often get calls in the University of Georgia Cooperative Extension office from homeowners who ask, “What is this black stuff on the leaves of my crape myrtle and gardenia?” My answer is sooty mold.
Sooty mold is a secondary problem that is caused by an infestation of aphids, whiteflies or scale insects. It frequently develops on the foliage of many ornamental plants in the summer. It covers the top surface of leaves which reduces the photosynthetic process.
Sooty mold often goes unnoticed until a large number of leaves are covered with a black unsightly substance. It is not really a disease, but a black fungal coating on the leaves.
Insects can't be far away
Sooty mold indicates an insect problem on the plant. The insects feeding on the plant excrete a sugary substance called honeydew. In the summer months when aphid or whitefly populations are high, plants may look like vegetable oil has been poured on them. This shiny substance is honeydew.
Summer rains help rinse this substance away and may even delay the onset of the sooty mold. However, if there is insufficient rain to rinse off the honeydew, it will stick to the leaves. Sooty mold fungus does not feed on plant tissue, but on the secretions from the insects that are feeding on the plant.
Aphids, scales, whiteflies and other sucking insects primarily cause sooty mold to form on plants like fig, crape myrtle, azaleas, tulip tree, oleander, and other ornamentals. The feeding of a large number of these insects and the coating of the sooty mold may lead to reduced vigor in the plant. These sucking pests take in large amounts of sap. Much of the water and sugars in the sap pass though the insect and onto the leaf.
Remove insects to control sooty mold
To control sooty mold, control the aphids, scales or other pests that are creating the honeydew. Aphids can often be washed off by a strong spray of water from a water hose. This may also remove some of the honeydew and sooty mold. Remaining sooty mold will eventually dry up and flake off the leaves.
To control heavy infestations of aphids, scales and mealy bugs, on ornamental plants, use acephate, imidacloprid, malathion or other recommended insecticides. Read and follow the pesticide label carefully.
Controlling insects will in turn prevent the eyesore sooty black mold from forming on plants in your landscape. Plan now to take action to prevent this issue from being a problem later in the season.
William Tyson is the UGA Extension coordinator for Bulloch County.