Often called privets, Ligustrum (Ligustrum spp.) are shrubs or small trees that feature dense foliage, dark green or golden-yellow leaves and showy flower clusters that bloom in late spring and early summer. Commonly grown species include the Japanese privet (Ligustrum japonicum) and the glossy privet (Ligustrum lucidum), both Asian natives that thrive in U.S. Department of Agriculture plant hardiness zones 8 through 10. These tough, hardy plants quickly grow into privacy screens, informal hedges or border shrubs, but you must watch out for several pests.
Privets attract various types of scales, including pittosporum scales (Asterolecaniidae spp.), soft black scales (Saissetia oleae) and California red scales (Aonidiella aurantii). These tiny, sap-sucking pests often look more like little growths on plant tissue than actual insects. Adult females reproduce without males, laying eggs that they hide with their bodies. After the eggs hatch tiny crawlers emerge to find a suitable feeding spot where they typically remain for their entire life cycles. Small scale populations won't harm privets, but high numbers of soft black and California red scales can cause the leaves to yellow, wilt and fall from the shrub. Severe infestations weaken plants and cause slowed or stunted growth. Soft black scales also secrete honeydew, a sugary material that attracts sooty mold fungi. Pittosporum scales cause round pits to develop on infected twigs, causing swelling, distortion and possibly death of the wood tissue.
The black vine weevil (Otiorhynchus sulcatus) can be a very destructive privet pest since all stages cause injuries. Adult weevils reach about 1/2 inch in length, with dark brown to black bodies and yellowish markings. The nocturnal weevils come out at night to chew notches on leaf edges. Adult females lay eggs in the soil beneath host privet plants, and the white larvae emerge in mid-summer to feed on the tender roots. Larvae-infested shrubs exhibit reduced growth and withering, yellowing or browning foliage. Uncontrolled infestations can eventually kill affected privets.
Various mite species occasionally infest privet plants. Mites are tiny pests that group together on the undersides of leaves to feed. Eriophyid mites cause hard swellings to form on twigs and raised, brown or green blisters to develop on the foliage. Affected leaves sometimes curl up and look misshapen. Various spider mite species sometimes attack privets. These tiny arachnids suck sap out of leaves, causing small, discolored dots to appear on the foliage. Large spider mite populations can cause the leaves to turn bronze, yellow or red before dropping from the shrubs.
4. Controlling Pests
Foliar sprays aren't effective against black vine weevils, so get rid of the pests by knocking them off the plant into a bucket of soapy water. You can often get rid of minor spider mite infestations by blasting the pests off the foliage with a strong spray of water from a garden hose. Pruning out damaged foliage helps manage minor scale and mite infestations, but insecticidal soap sprays might be needed to control severe infestations of either pest. Scales have hard layers of protective platelike shell or wax protecting their bodies, so chemical treatments must be timed to coincide with the crawler phase. Following the directions on the product's label, mix 2 1/2 to 8 tablespoons of insecticidal soap product into a gallon of water. Spray the foliage thoroughly since the spray must actually touch the pest in order to work. Repeat applications every four to seven days until pest populations are under control. Avoid spraying your privet when temperatures soar over 90 degrees Fahrenheit or you risk damaging the foliage.
- University of California Statewide Integrated Pest Management Program: Privet- Ligustrum Spp.
- Colorado State University Extension: Insect Control: Soaps and Detergents
- University of California Statewide Integrated Pest Management Program: Spider Mites
- Missouri Botanical Garden: Ligustrum Japonicum
- Cal Poly Urban Forest Ecosystems Institute: Glossy Privet
- University of California Statewide Integrated Pest Management Program: Scales
- University of California Statewide Integrated Pest Management Program: Pit Scales
- University of California Statewide Integrated Pest Management Program: Gall and Blister Mites (Eriophyid Mites)
- University of California Statewide Integrated Pest Management Program: Black Vine Weevil