Cottony Maple Scale

Cottony Maple Scale (Pulvinaria innumerabilis)

Identification: A soft scale (family Coccidae). Females are 3–6 mm, brown and flat when young, producing a prominent white cottony egg sac up to 12 mm long in late spring that makes infestations visually unmistakable. The white masses on silver and red maple twigs in May–June are a reliable identification feature. P. innumerabilis is one of the most recognized scale insects in the eastern US due to this dramatic egg sac production.

Life cycle: One generation per year in Tennessee. Overwinters as mated females on twigs and bark. Eggs are deposited in cottony masses in May–June; crawlers emerge June–July and migrate to leaf undersides to feed through summer. In late summer crawlers return to bark, mature, mate, and settle for the winter. The crawler-on-leaves summer phase is the optimal spray window.

Damage signs: Heavy infestations cause twig dieback, branch decline, and severe honeydew drip that coats sidewalks, cars, and surfaces under infested maples. Sooty mold on honeydew-coated leaves and surfaces is a common secondary complaint. Silver maple (Acer saccharinum) is the primary host; boxelder, linden, dogwood, and euonymus are also susceptible. Populations can explode in years following warm winters.

Treatment window: Late June through July targeting crawlers on leaf undersides — the most accessible and vulnerable life stage. Treating egg sac adults in May is largely ineffective.

UT-recommended approach: Insecticidal soap or horticultural oil applied to leaf undersides in late June–July. Systemic imidacloprid soil drench applied in early spring provides uptake at crawler settling time. Avoid treating the white egg-sac stage — the cottony mass protects eggs from contact materials. A single well-timed crawler spray is usually sufficient to reduce populations significantly.