Cottony maple scale: what the extension services record

This page describes what the named sources say. It is not a diagnosis of any tree and does not say what should be done with one. None of the five pages read lists cottony maple scale as regulated or notifiable. Each section names its source, all read on October 9, 2026. The scale has a row in insect pests of trees, and the armored scale that shares that table is covered on oystershell scale.

Names

Penn State Extension, Ohio State Extension, The Morton Arboretum and Utah State University Extension give the scientific name Pulvinaria innumerabilis. The University of Delaware's June 2025 fact sheet says the species was formerly Pulvinaria innumerabilis and is now Neopulvinaria innumerabilis, and uses the term pulvinaria scale for any species in or formerly in that genus, including cottony maple leaf scale and cottony camellia scale. Ohio State says the scale is sometimes confused with the cottony maple leaf scale, whose females form their egg sacs on leaves, not on branches. The Arboretum says the insect is native to North America.

Hosts

Penn State says the favored host is silver maple and that a large number of other deciduous trees are attacked, naming boxelder, basswood, white ash, dogwood, locust, hackberry, sycamore, birch, elm, willow and poplar. Ohio State says it commonly attacks silver and red maples in Ohio, can reach epidemic numbers on silver maple, and survives on other deciduous trees and shrubs including honey and black locust, oak, rose and sumac. The Arboretum names silver maple and boxelder as the primary hosts and lists other maples, white ash, hackberry, dogwood, beech, apple, oak, linden, elm and locusts. Delaware says it is frequently found on red or silver maples. Utah State says it is most common on maple and has many hosts.

What the scale looks like

The sources describe a soft scale, a group the Arboretum says is usually larger than armored scales and covers itself with waxy secretions. Penn State calls it one of the largest and most conspicuous soft scales. It says mature females are pale to dark brown, convex and about 3 to 6 mm long, and that the egg masses on twigs and branches are the easiest way to recognise the insect. Ohio State says mature females are flat, oval and brown, a quarter to three-eighths inch across, and Utah State gives 1/8 inch. The egg masses are white and cottony. Penn State says each usually holds 1,000 to 1,500 eggs, Ohio State says over 1,500, and Delaware says up to 1,000 in a sac about 1/4 inch long. Ohio State describes the cotton as a waxy secretion around the sac, and the Arboretum compares the mass to a piece of popcorn.

Life cycle as the sources state it

The Arboretum and Utah State give one generation a year. The scale overwinters as an immature, a second instar nymph on the bark of twigs and branches according to Penn State and Utah State, and as immature females according to the Arboretum and Ohio State. Females mature and lay the egg masses in late May to June, and Penn State says laying continues through late summer. Crawlers hatch from mid-June through mid-July in Penn State's account, mid-June to August in Ohio State's, June through July in Utah State's, and early July in Delaware's. The crawlers move to the underside of leaves, feeding along veins and the midrib. Males mature in late summer, mate and die, and the Arboretum says they lack feeding mouthparts and die a few days after mating. Before leaf drop the immature females move back to twigs and attach to overwinter.

Damage and honeydew

Penn State says severely infested trees look as if they were covered with a string of popcorn, that heavy populations cause twig and branch dieback, that under severe conditions an infestation may kill the entire tree and that foliage can drop early. All the sources record honeydew, the sticky excreta, and black sooty mold growing on it. Ohio State says honeydew is often mistaken for tree sap dropping on cars and sidewalks and attracts bees, wasps and ants, and that in rare cases heavy infestations have killed stressed or weakened trees. It calls the scale normally a mere curiosity and a nuisance. The Arboretum says it is considered a minor pest in most years, that the population rises dramatically every few years, and that natural predators then rise and reduce it over time. Ohio State notes that parasites and predators normally keep numbers in check, and Delaware names wasps, lacewings, lady beetles and birds, sparrows in particular.

Status and reporting

None of the pages names a regulation, quarantine or report line. This page gives no treatment steps, product names, rates or timings. For who may apply pesticides see pesticide licences.