Hydrangea scale

Hydrangea scale (Pulvinaria hydrangeae) is a sap-sucking insect belonging to the family Coccidae, order Hemiptera. This pest is a common concern for horticulturists, as it can cause serious stress to ornamental shrubs if left unchecked in gardens and landscapes.

The pest primarily targets hydrangea species, but it has a broad host range including maple, linden, viburnum, and dogwood. It is particularly problematic in nurseries and sheltered garden environments where the lack of natural predators allows its population to grow rapidly during the season.

The lifecycle of the hydrangea scale usually involves one generation per year. Second-instar nymphs overwinter on the bark of twigs. As temperatures rise in spring, they complete their development into adults. By early summer, females produce distinctive, fluffy white ovisacs filled with thousands of eggs, which are clearly visible on the host plant.

Damage occurs as nymphs and females feed on the sap of the plant. Infestation leads to leaf chlorosis, curling, and premature leaf drop. Furthermore, the sticky honeydew secreted by the scale insects encourages the growth of sooty mold, which creates a black, unsightly layer on leaves and stems, severely hampering the plant's ability to photosynthesize.

Effective management requires a multi-stage approach. Applying horticultural oils or systemic insecticides in early spring can help control overwintering nymphs. During the summer, when the mobile "crawlers" hatch, targeted insecticide applications are most effective. Cultural practices such as pruning and destroying heavily infested branches are crucial to reducing the pest population.