Having an evergreen, fruiting holly tree or bush (Ilex spp.) guarantees you armloads of decorative, spiny-leaved red-berried branches to fill your home with that festive year-end holiday spirit. More than 400 varieties of hollies grow across U.S. Department of Agriculture plant hardiness zones 5 through 10, depending on species. While they differ widely in size, climate preference and berry color, hollies share susceptibility to leaf-blackening sooty mold. This unsightly fungus feeds on the sticky honeydew resulting from aphid or scale insect infestation.
Inspect the holly for pear-shaped, yellow, green, brown, red or black aphids on the undersides of young leaves and lining the young stems. Branch- and leaf-infesting soft scales have hard white, grayish, brown or black coverings. They frequently resemble tiny barnacles.
Remove light aphid infestations and rinse off honeydew with a strong blast from the garden hose. Scrape small numbers of scales from the plants with a soft toothbrush.
Prune heavily infested foliage and branches and place them in sealed bags for disposal. This method works best on dense, large hollies where the loss of branches won't be too noticeable.
Treat persistent aphid or scale infestations by saturating the holly's leaves and branches with a ready-to-use insecticidal soap spray applied according to the label specifications. If you wish, mix your own solution by adding 5 tablespoons of liquid dish detergent to 1 gallon of soft water. This non-toxic insecticide suffocates the insects without endangering kids, pets or beneficial insects.
Eliminate honeydew-feeding ants that protect aphids and scales. Set sugar-based boric-acid ant baits along the foraging trails leading to the holly bush. The ants carry the low-toxicity bait back to their nest, where it gradually kills the queen and entire colony.
Allow the sooty mold to dry up and weather from your holly bush once the insects and honeydew are gone. If the plant's appearance bothers you, speed the process with a strong soap-and-water spray. To remove especially stubborn sooty mold, scrub the leaves with a soft cloth dipped in the soap-and-water solution.