Privet is also known as ligustrum and is commonly used as a hedge, shrub or tree. There are a variety of ligustrums used in landscaping, such as Japanese privet, glossy privet and Chinese privet. The rapid growth of this plant has made it an ideal landscaping choice. However, privet is susceptible to insect infestations that can affect its health and vigour. Aphids often attack privet and require control when infestations are heavy.
Aphids are small insects that colonise on the undersides of privet leaves. This soft bodied pest is red, green or black in colour. Aphids cause damage to host plants by feeding with their piercing mouthparts. Certain types of aphids carry viruses and transmit them to plants.
Aphid feeding often causes privet leaves to wilt and turn yellow from the high amounts of sap being removed from plant leaves. Although the damage makes the hedge unsightly, aphid feeding does not usually cause the death of the plant. Some plants infested with aphids may become distorted from feeding. Aphids excrete a sugary substance known as honeydew, which is deposited on plant leaves. This causes a black fungal coating known as sooty mould to develop on the plant. Sooty mould is a sign of heavy insect infestation.
Removing aphids from your privet hedge is often accomplished by spraying your plant with hard streams of water twice each week. This process knocks aphids from the plant leaves. Natural predatory insects often feed on aphids. Lacewings and lady beetles feed on aphids and can keep small infestations under control. Insecticides cannot be used with natural predatory insects for aphid control because it will kill the beneficial insects.
Horticultural oils are often effective in controlling aphids on privet hedges. These products work by smothering the insects or disrupting the way they feed. Check the manufacturer label before using to ensure it is safe for use on privet. Insecticides that work on the nervous system are also used in aphid control. For information on insecticides for aphid control, consult your local extension office.