Holly Scale

Holly scale is an armored scale insect in the family Diaspididae that feeds primarily on American holly (Ilex opaca), English holly (Ilex aquifolium), and related broadleaf evergreens including yew and boxwood. Adult females spend their lives anchored to host tissue beneath a small, circular, waxy cover roughly 1.5 to 2 millimeters across. In upstate New York gardens, populations tend to build on foundation plantings and hedgerows with poor air circulation, often going unnoticed until foliage begins to yellow or branches die back.

The scale overwinters as fertilized adult females on leaves and stems. In late spring to early summer, mobile first-instar nymphs called crawlers emerge, disperse across the plant, and settle to feed. Once a crawler forms its protective waxy armor, contact sprays become far less effective. That brief crawler window is the most productive time to intervene. One generation per year is typical in cooler climates. Heavy, multi-season infestations are the main cause of serious plant decline, since individual scales cause little damage but dense colonies extract enough sap to disrupt normal growth.

Holly scale is a sap-feeding pest that weakens and can kill hollies and other broadleaf evergreens through sustained feeding by colonies of nymphs and adult females on leaves and stems.