Cottony Maple Scale (Pulvinaria innumerabilis) is a soft scale insect pest that commonly attacks maple trees, but can be found on a variety on hosts. Usually it is just a nuisance, but in very severe infestations, it can kill weakened trees or branches on otherwise healthy trees. These scales are usually first noticed when females produce egg sacs which appear as small cottony balls.
Cottony Maple Scale Life cycle
Cottony Maple Scale has one generation per year, and understanding its life cycle is crucial for management of this pest, because not all pesticides will be effective at all insect life stages.
Mature cottony maple scales are small, flat, oval, and brown scales 1/4 to 3/8-inch in diameter, that can attach themselves firmly to tree branches. Female cottony maple scales produce the white ovisacs that look like cotton balls. These “cotton balls” are actually sacs which may contain up to 1,500 individual eggs.
Young nymphs hatch from these eggs in summer. Cottony maple scale nymphs are small, flat, oval insects that crawl on leaves and attache themselves to the undersides of leaves. As they grow and develop, the produce honeydew, excess water and sugar exudates, on the leaves.
In early fall, the male scales emerge as tiny winged insects that search around for females to mate with. After mating, females crawl onto woody branches or twigs where they attach themselves. Females at this stage are slightly green with a white powder coating and are about 1/8-inch long at this stage. In winter, the cottony maple scale females change colors and overwinter on the trees. They do not fully mature until the following spring, after which they begin to produce the white cottony egg sacs.
Cottony Maple Scale Damage
Cottony Maple Scale damage can very in severity by level of infestation. The honeydew produced by nymphs on leaves can cause secondary infections of sooty mold, a gray black fungus. The honeydew can also attract wasps and ants. Severe damage usually only occurs on otherwise weakened or stressed trees.
Integrated Pest Management Techniques and Control
There are some special considerations when deciding on a pest management strategy for cottony maple scale. Overuse of pesticides, if not applied with the proper timing may actually increase cottony maple scale populations. This is because there are number of natural predators, such as parasitic wasps and adult lady beetles, that keep cottony maple scale populations in check. Some pesticides may damage these predators and increase pest the population as a result. Maintaining and supplementing these predators should be carefully considered in any pest management program.
Some “soft” pesticides such as soaps and oils can be very effective in controlling the nymph crawlers on leaf surfaces in summer. These types of pesticides kill only on contact, so they usually have minimal adverse affects against adult lady beetles or parasitic wasps. Using soaps and oils at higher rates can have phyto-toxic affects on leaf tissue, however, so 1.5% application rates are recommended.
Standard chemical pesticides also should only be used at this time, from June – August to kill the crawling nymphs. Specific products should be carefully considered to avoid killing beneficials.
Oils can also be used during winter to control the overwintering females. However, some maple species are sensitive to oils and this should be considered, to avoid spring leaf die-back.
Ohio State Extension Factsheet, David J. Shetlar