Ficus nitida (Ficus microcarpa nitida syn. Ficus retusa var. nitida) is an attractive shade tree with a rounded canopy that can measure up to 80 feet wide. The ideal tree to hold a tire swing for the kids, it's grown outdoors in U.S. Department of Agriculture plant hardiness zones 9 through 11 and does well indoors in cooler regions. Like most ficus species, this one is grown for its attractive, smooth, evergreen foliage. Brown spots on the leaves not only detract from the tree’s attractiveness, but they also could be a sign of a deadly disease.
1. Fungal Problems
Anthracnose is a fungal disease caused by any of a number of fungal pathogens that attach themselves to the above-ground parts of the ficus. Symptoms include partially dead leaves and small foliage spots that may be brown in color. The disease typically strikes newer leaves. Southern blight is another fungal disease, caused by Sclerotium rolfsii, and it is much more deadly than anthracnose. This pathogen infects the ficus’ roots, and by the time above-ground symptoms appear, it is too late to save the plant. These symptoms include brown spots on the leaves. If the spots appear after several rainy days with temperatures between 86 and 95 degrees Fahrenheit, suspect southern blight.
If the brown spots are raised bumps, and you notice a sticky substance on the leaves, suspect an infestation of brown soft scale (Coccus hesperidum). A heavy scale infestation may cause the ficus tree’s leaves to turn yellow and drop prematurely. Ficus retusa is the preferred host of Cuban laurel thrips (Gynaikothrips ficorum), according to entomologists with the University of Florida. Look for small purple to brown spots along the leaf’s mid-rib, leaf curling and premature leaf death.
3. Disease Prevention
Fungal spores are often introduced to plants when rainwater or irrigation water splashes infested soil onto the foliage. Minimize this risk by never watering the ficus overhead, but at the soil. Rake up leaves and other plant debris from around the base of the tree and prune out infected stems and branches. Don’t allow the ficus tree to become stressed for water. Since there is no cure for southern blight, prevention is imperative. Remove an infected ficus and the soil from a 6-inch radius around the plant and 6 inches in depth. Replace this soil with sterile potting soil. If you’ve had problems with southern blight in the past, spray the ficus tree with a fungicide that contains triadimefon as the active ingredient. This won’t cure an infection but acts as a preventive measure. Mix 1/4 teaspoon of the fungicide in 1 gallon of water in a backpack sprayer, hand pump sprayer, or a hand-held spray gun and spray the entire tree until the fungicide drips off. Repeat the application every two weeks.
4. Pest Management
Scales are easily controlled with horticultural oil sprays. Spray the entire tree until the products drip. If the pests occur on a small indoor tree, a cotton swab dipped in rubbing alcohol wiped on the scale will kill it. Manage Cuban laurel thrips by starving them. Since they only attack the new growth on small trees, remove all new growth at the first sign of an infestation.