Matt,

Have you happened to notice any pests? Hidden maybe? If not on your citrus tree, take a close look on that Draceana. They are notorious for harboring those.

Try and remove the sooty mold from your tree after you've eliminated the insects. Wipe the parts of the tree you can reach, using a soft cloth saturated with a detergent-free soap-and-water solution. Use a heavy water spray to dislodge the fungus from higher branches.

Sooty mold usually indicates that your citrus trees have an insect infestation. It is usually found on the bottom of a tree's leaves. The insects that cause sooty mold--mealybugs, white flies and aphids--are typically more active during cooler weather. Mold forms from a honeydew secretion that the insects leave after feeding on the tree. You can remove sooty mold with store-bought insecticides or homemade solutions.

You could,

Mix only one of the following: 2 tbsp. of tea tree oil to 2 cups of water, 20 drops of grapefruit seed oil to 2 cups of water, 1 cup of apple cider vinegar to 2 cups of water, or 2 tsp. of hydrogen peroxide to 3 cups of water.

Fill a garden sprayer with the chosen mixture. A garden sprayer is a nozzle for your garden hose with a plastic bottle attached to its underside. As you spray, the bottle's contents mix with the water. Turn the nozzle to its widest spraying range to coat the foliage evenly.

Spray mixture up into the branches, dampening all the foliage you can reach. Redirect the spray over the top of the tree so the mixture dampens the upper foliage as well.

Allow the foliage to soak under the mixture for about two hours. Spray the tree thoroughly twice more. Allow the tree to soak overnight.

Rinse the tree thoroughly with water. Most of the mold should come off as the tree is being rinsed. Any of these mixtures will also repel or kill the pests causing the mold.

Mike

Mike, I appreciate you taking the time to explain that. This has never happened. I had seen pics on google that had white insects and scale along with the mold. I looked over the plant in September didn't see any scale but I will look again. Probably because of the dark black I didn't see them. I will try the home remedy first.