White Bugs Killing a Holly Shrub

Holly shrubs (Ilex spp) are widely grown hedge and foundation plants. They thrive in rich, consistently moist well-drained soil and sun or partial shade. Many holly species have the glossy, spiny green leaves and bright red berries familiar as winter holiday decorations. Infestations of white bugs on a holly's twigs are easy to spot, but not always easy to remove. Left unchecked, however, these tiny white pests can seriously weaken or kill holly bushes.

Wax scales (Ceroplastes ceriferus) are small, round flat insects between one-eighth and one-quarter of an inch long. Their lack of distinct heads and tails make scales difficult to identify as insects. As larvae, the insects secrete a waxy substance that hardens into a protective dome and accounts for their name. While wax scales infest several holly varieties, they are most common on Chinese and Japanese shrubs. White to pale pink greedy (Hemiberlesia rapax) and oleander (Aspidiotus nerii) scales also attack -- but rarely damage -- holly shrubs.

Female wax scales overwinter on infested plants and lay their eggs in mid- to late spring. Each female can lay as many as 3,000 eggs. Larvae hatch from two weeks to a month late. Depending on the climate, they emerge between early and late June. Male larvae live only a few hours. The female larvae mature by August, and attach themselves to the holly's stems and twigs. They avoid the leaves unless their numbers are very large. The insects survive by piercing the bark with their mouthparts and feeding on the plants' fluids.

Holly shrubs suffering from heavy wax scale infestations may develop cracked, oozing bark, branch dieback or yellowing, wilting leaves that drop early. Wax scales also produce honeydew, a sweet, sticky waste product that covers the branches. Honeydew may attract ants and the sooty mold fungus. The honeydew-eating ants protect the scales from natural predators. Sooty mold's spores feed on the honeydew, covering it with a black powdery substance. If the black mold gets on the holly shrub's leaves, it may reduce photosynthesis and further weaken the shrubs. Chinese and Burford holly bushes are especially susceptible to sooty mold. Young holly plants with repeat scale infestations over several years may die.

Spraying wax scale-infested holly shrubs with carbaryl-based insecticides as soon as larvae begin hatching in June is effective against heavy infestations. A single application is usually sufficient to kill all the insects. Manual removal of small numbers of wax scales also works. Destroy the insects you remove between February and April. Any scales dropped on the ground in autumn or winter will die.