In a perfect world, properly maintained and regularly pruned privet (Ligustrum spp.) hedges would guarantee dense, green- or golden-leaved barriers defining and dividing your outdoor spaces. The reality is that privets have their share of disfiguring pests, including two white, sap-sucking insects. Left unchecked, both weaken and blemish privet hedges with their feeding. The good news is that, if you catch them early, banishing these pests is relatively simple.
Nearly two male euonymus scale insects (Unaspis euonymi) could dance on the head of a pin, if dancing weren't beyond the talents of these slender creamy-white pests and their larger, gray to dark-brown mates. Euonymus scales drain privet sap with their sharp, strawlike mouths and produce tiny, yellow offspring. The nymphs hatch in late spring or early summer, depending on where in U.S. Department of Agricultural plant hardiness zones 4 through 10 their host privets grow. They leave their mother's protective shells to attach to the plants and feed before growing their own waxy armor. The male nymphs mature into winged insects before mating. The summer-hatched second generation develops into mature, fertilized females that overwinter on the plants until spring.
Even as occasional privet pests, euonymus scales may do serious damage. Light infestations cause yellow leaf spotting. Heavier ones may cover the foliage and stems, compromising photosynthesis and resulting in leaf loss, stunting or partial to complete dieback.
Scraping scales from small privets with a scouring pad or toothbrush often eliminates the problem. On a fully grown hedge, however, you may have to prune and dispose of affected branches. While the adult scale's protective shells render pesticides ineffective, ready-to-use horticultural oil suffocates nymphs before they attach. Wearing protective clothing and eyewear, apply the oil to a well-watered hedge at a temperature between 40 and 90 degrees Fahrenheit. Cover your entire hedge to the run-off point or at the label's specified rate. Pay particular attention to the leaf and branch undersides.
Citrus whiteflies (Dialeurodes citri) target privet hedges growing from the mid-Atlantic States through the Gulf Coast, the Southwest and California. The flies overwinter on leaf backs as late-stage nymphs before maturing and depositing their eggs in spring.
Like scales, the immobile nymphs and tiny, white four-winged adults feed on sap, exacerbating the problem with gooey, high-carbohydrate waste called honeydew. When airborne sooty molds find honeydew-laden privets, the result is a hedge covered with unsightly layers of powdery, black fungal spores. Heavy sooty-mold infestation may weaken the plants by blocking photosynthesis.
Blasting your privet hedge with a strong spray of water from a garden hose, pruning its lightly infested leaves or vacuuming the adults with a handheld vacuum and freezing them overnight before disposing of them controls early whitefly infestations. To manage a serious attack, spray your hedge with ready-to-use horticultural oil applied as if you were treating a euonymus scale attack. Once again, thorough leaf coverage is critical to destroy the immobile whitefly nymphs. Using oil to treat the flies also eradicates sooty mold.
- Penn State Woody Ornamental Integrated Pest Management: Euonymus Scale Fact Sheet
- Manual of Woody Landscape Plants, Fifth Edition; Michael A. Dirr
- University of California Statewide Integrated Pest Management: Scales
- Sunset.com: Scale Insects
- University of Minnesota Center for Urban Ecology and Sustainability: Citrus Whitefly
- University of California Statewide Integrated Pest Management Program: Sooty Mold
- University of California Statewide Integrated Pest Management Program: Whiteflies
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