Standing strong against coastal winds, black olive (Bucida buceras) is useful for ocean-front landscape and container planting in U.S. Department of Agriculture plant hardiness zones 10 to 11. Uncommon outside Florida and South America, black olive resists most pests and diseases, with the exception of sooty mold, a fungus often seen as a soot-like coating on leaves and stems of various plants. Sooty mold does little harm, but it is evidence that your black olive is infested with some tiny, sap-sucking pests. Sucking insects such as aphids, whiteflies and mealybugs excrete the honeydew that sooty mold grows on. Sooty mold goes away when the pests do.
Clean sooty mold from the leaves with a moist paper towel, or spray the black olive tree with a strong jet of water from a hose. A strong jet of water will also help remove the pests that are causing the problem. Once the pests are gone, sooty mold may weather away in wind, rain and sun.
Mix 2 tablespoons of baby shampoo in 1 gallon of water, using only a maximum of 6 tablespoons of baby shampoo per 1 gallon of water, to make a soap solution. Spray a small spot of the black olive, and wait two to three days. If the black olive shows no signs of damage, water it until at least the top 3 inches of soil is moist to prepare it for an application of the soap.
Spray the leaves with the soap, coating the leaves all over to the point of drip-off. The spray safely kills aphids and other harmful pests, including black scale, which targets black olive trees. Rinse the soap from the black olive a few hours after the application. Repeat applications every five to seven days.
Prune low-hanging branches within 3 feet of the ground in the spring, while the black olive is dormant. Black olive has branches that bend towards the ground, which makes it more attractive to ants that feed on honeydew and protect honeydew-producing pests from beneficial insects. Proper pruning will keep ants off the tree and prevent overgrowth of new plant tissue, which attracts the pests.
Things You Will Need
- Moist paper towel
- Baby shampoo
- Sooty mold may develop naturally on small parts of the plant without a pest infestation; always check for pests before treating.
- Black olive can be treated with a dormant oil spray while still dormant in the spring to prevent pests.
- Ants may be further controlled with bait stations.
- Overfertilizing may stimulate growth that attracts pests. On average, it is best to fertilize monthly with a balanced fertilizer with a composition rating of 10-10-10.
- University of Florida IFAS Extension: Black, Sooty Mold on Landscape Plants
- University of Wisconsin: Sooty Mold
- University of Arkansas: Sooty Mold of Woody Ornamentals
- University of California: Black Scale
- University of Florida: Black Olive
- University of Florida: Home Remedies for Insect and Disease Control on Plants
- Pat Welsh's Southern California Organic Gardening: Black Olive Tree
- University of California: Sooty Mold