The cottony maple scale (Neopulvinaria innumerabilis) produces egg masses on the twigs and small branches of the host. Egg masses are white and cottony and laid out along stems. The cottony maple leaf scale (P. acericola) is easily confused with the cottony maple scale, except the egg sacs of this species are produced on the leaves of the host plants. Neopulvinaria innumerabilis is one of the largest of the scale insects that attack ornamental plants in the United States. It has been reported in almost every state and also several Canadian Provinces. The scale overwinters as an immature female who may be difficult to see and is flattened on the twigs of the host. Once temperatures warm in the spring, the female matures rapidly and by late spring the white ovisac is visible and may contain up to 1,000 eggs laid by each adult female. By late June and July, tiny mobile crawlers begin to appear at which time they move to the undersides of leaves of the host, where they feed with piercing-sucking mouthparts. During the summer, the scale can spend time on either leaf surface. Males mature by the end of the summer and emerge as winged individuals and strangely, according to the literature, are capable of mating with the immature females. Unfertilized females can also produce eggs, but they will all become males. By the fall, the immature females move back to the stems and overwinter there. A single generation of the cottony maple scale occurs per year.
The cottony maple scale may be confused with the cottony maple leaf scale (Pulvinaria acericola), which only lays its eggs on the leaves (not twigs and small branches) of its hosts. Pulvinaria acericola adult females are maroon in color, just prior to production of eggs. This species overwinters as a partially grown nymph feeding on host plant twigs and branches. Males mature and (also, like the cottony maple scale) mate with immature females in April and by May the mature females of this species migrate to host plant leaves to lay their eggs in a white ovisac which may contain up to 2,500 eggs. By the end of June, eggs of Pulvinaria acericola may hatch and nymphs settle along the leaf veins. Immature cottony maple leaf scales are pale green in color and not easily seen without magnification. They stay on the leaves until the fall, at which point they migrate to branch and twig bark.
Honeydew and sooty mold may be found on the leaves and branches, twig dieback, premature loss of foliage, and in very extreme conditions death of the host may occur when cottony maple scales are present. The cottony maple leaf scale may also cause premature leaf drop, and sometimes the death of host plant twigs and branches.
Look for white, cottony egg masses associated with the adult females during the late spring as this is the most conspicuous stage of these insects. Scout for immature females overwintering on the twigs or crawlers on the undersides of leaves by June and July. Management may not be necessary unless populations are high and damage is occurring.
Maintain host plant vigor; otherwise cultural management options for these scales are limited. Prune out and destroy heavily infested branches, if practical.
There are many important natural enemies of these insects including wasp and fly parasites and lady beetle predators which attack immature scale stages. Certain species of birds may also feed on the adult female scales. A number of natural enemies attacks Neopulvinaria innumerabilis including wasp and fly parasites and various lady beetles. (Coccophagus lycimnia, Leucopis alticeps, Leucopis silesiaca, and Exochomus quadripustulatus (Bolu, 2012 and Pellizzari, 1987).) Certain species of sparrow attack cottony maple scale females. Several parasites of Pulvinaria acericola have been reported in the literature, but their effectiveness at managing pest populations of the cottony maple leaf scale is unknown.
Abamectin (NL)
Acephate (NL)
Acetamiprid (L)
Azadirachtin (NL)
Buprofezin (NL)
Carbaryl (L)
Chlorpyrifos (N)
Clothianidin (NL)
Cyantraniliprole (NL)
Cyfluthrin (NL)
Dinotefuran (NL)
Flonicamid+cyclaniliprole (N)
Gamma-cyhalothrin (L)
Horticultural oil (L)
Imidacloprid (L)
Insecticidal soap (NL)
Lambda-cyhalothrin (L)
Neem oil (NL)
Pyrethrin+sulfur (NL)
Pyriproxyfen (eggs) (L)
Spinetoram+sulfoxaflor (N)
Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), dinotefuran (soil drench), imidacloprid (soil drench), and neem oil (soil drench).
Dormant oil usually not recommended due to plant sensitivity, particularly with maple; read and follow all label instructions for safety and proper use.
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022 neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
