Cottony Maple Scale

Pulvinaria innumerabilis

The overwintering form of the cottony maple scale is a small, brown, flattened 1/8 inch long scale attached to the bark of twigs and small branches. During the summer, the scale enlarges by secreting wax resulting in a body several times greater than the overwintering form. The body of the scale is white and resembles a kernel of popcorn. The immature scale is flat, oval shaped, and light yellow to green. The eggs are usually brown.

Life History
The cottony maple scale is common on maple, boxelder, hackberry, dogwood, beech, apple, oak, linden, honeylocust, and elm. The scale overwinters as an immature female on the twigs of the host. By late spring the insect has developed into a mature female and begins laying as many as 1,000 eggs. The eggs hatch into crawlers in late June and July and move from the twigs to the leaves where they feed along the midrib or the veins. Late in the summer, mature winged males mate with immature females. The males die within a few days after mating as they are unable to feed. Before leaf drop in the fall, the immature females move back to the twigs to overwinter. There is one generation per year.

Cottony Maple Scale on Silver Maple Leaf
Figure 2. Cottony Maple Scale on
Silver Maple Leaf

Damage to the host tree is caused in several ways. If scale populations are heavy, dieback of branches and twigs may result. In severe cases the tree may die. Feeding by the scales may result in heavy concentrations of honeydew. This honeydew is readily colonized by sooty mold fungi which will result in a blackened appearance to leaves, twigs, and branches. In some cases, premature leaf drop may also occur due to scale feeding. The honeydew also becomes a nuisance due to deposits on automobiles and lawn furniture located under infested trees.

Nonchemical Control
There are a number of natural enemies of the cottony maple scale including a number of wasp and fly parasites. Natural predators such as various species of lady beetles feed on the immature scales situated on the leaves. Outbreaks generally buildup over a period of years and then disappear due to natural enemies and climatic factors. Well established and vigorously growing trees are usually able overcome the infestation.

Wasp Parasite of Cottony Maple Scale
Figure 4. Wasp Parasite
of Cottony Maple Scale

Chemical Control
If scales are heavy on stressed or unestablished trees, a crawler spray may be applied in July in order to prevent dieback and decline. A dormant oil spray applied to the trunk and branches of the tree may also be used to reduce overwintering female populations and eliminate the risk of killing off beneficial insects such as lady beetles and parasites.