Chinese privet (Lingstrum sinense) is one of some 50 species of similar woody shrubs imported to the United States. It spreads aggressively and is often planted as a hedge, hence its name privet, meaning "private" or "giving privacy." Pollen from Chinese privet is a severe allergen and the plant is poisonous to horses. It is susceptible to several diseases and insects, including a weevil that it brought with it from Asia.
Root and Stem Rot
Chinese privet is susceptible to rhizoctonia, a fungus that enters the roots of the plant and spreads up into the base of the stem. The fungus turns the roots mushy and brown, and they eventually disintegrate. An infected plant wilts and is stunted, with small leaves, and pale green or yellow leaves. Remove infected plants and promptly disinfect the tools that you used. There are fungicides available to treat fungi that attacks roots.
Aphids are slow-moving insects that suck fluids from leaves and tender shoots. They come in several colors, including green, brown, and black. Some have wings. Aphids can carry harmful viruses from plant to plant. They produce a sweet substance called honeydew that is attractive to ants and that can form a black growth on leaves called sooty mold.
Keep your plants free of weeds. Wash off areas infected by aphids. There are USDA-approved pesticides to control aphids. You can also introduce natural predators, including ladybugs and lacewings.
Small, winged thrips thrive in hot, dry conditions. Thrip larvae feed on tender tissue of leaves and flowers, leading to distorted growth, damaged leaves and flowers and the premature dropping of flowers.
You can wash thrips off with a hose, or introduce predatory lacewings, pirate bugs, and other predatory thrips and mites, available from garden supply centers. There are pesticides approved for use against thrips.
Scale insects, related to mealybugs, are protected by a kind of armor that looks like scales. Scale insects suck the sap from plants with piercing mouths. Adult females lose their legs and remain in one spot. Like aphids, scale insects leave a sweet honeydew that ants like and that can cause the growth of a fungus called sooty mold.
Numerous natural parasites are available that will eat scale insects, as are USDA-approved insecticides.
Most leaf spot is caused by fungi, although some varieties are caused by bacteria. The brown or black spots on the leaves are circular or ragged with edges that are yellow or look water-soaked.
When the plant is dry, remove the infected leaves. Rake and dispose of infected leaves collected at the base of the plant. Irrigate at the soil level, not by sprinkling. Prune to encourage the circulation of air. There are FDA-approved fungicides to help combat leaf spots.
Twig blight is caused by anthracnose, a fungus that causes cankers on stems and the leaves to dry and cling to the stems. Prune diseased branches during dry weather and disinfect your tools. Fungicides are available that combat anthracnose.
The Ligustrum weevil (Ochyromera ligustri)--a natural predator of the Chinese privet--was imported with the plant from Asia. Female weevils deposit their eggs in the seeds. The larvae destroy the seeds as they develop. Adults feed on the leaves.
Florida officials list the Chinese privet as an aggressive, noxious plant and regard the Ligustrum weevil as a natural ally in their efforts to kill the plant. Insecticides are available to kill this weevil.