Cottony maple scale or Pulvinaria innumerabilis, has made itself known to the Lake County region this June. Many maples have been affected by the sap-sucking insect that has about a five year resurgence rate in the area. It is best described as looking like popcorn along the stems of the maple, or other effected trees such as, beech, elm, honey and black locust, ash, euonymus, oak, dogwood, hackberry, sycamore, willow, popular, and basswood. The actual scale is brown, about 1/8” in diameter, without obvious legs or antenna, and attached to the branch, while the white cottony ball is the egg mass that can contain up to 1,500 eggs.
In mid-June through August, the young nymphs will hatch called scale crawlers, the only time of this insect’s life where it is mobile. The crawlers make their way out to the undersides of leaves, attaching themselves near the main veins to feed. During this time the crawlers nourish themselves with tree sap which produces honeydew, a side product that is a sticky-sweet, and is sometimes mistaken for tree sap. As the honeydew drops from the insects, it coats cars, lawn furniture, and plants below the tree. This creates secondary problems including the attraction of ants and wasps, and a gray-black fuzzy mold called sooty mold that grows on the honeydew.
In September, the males develop wings, mate with the females, and then die. The females depart from the leaves and move back onto the branches where they attach themselves permanently, loosing their legs and antenna.
Unless the tree is otherwise distressed, the defoliation the scales cause will just be unsightly for the season. Spraying harsh pesticides is usually not necessary and can actually kill the insect predators coming to devour the scales such as lady beetles and many small wasps. Seeing ripped open egg masses or small holes in the scale insect are the signs of beneficial insect activity. Soaps and summer horticultural oils can be effective in the management of newly hatched crawlers with minimal affects to beneficial insects.
If you ever need good plant advice, always contact your local extension’s Master Gardeners. As a former volunteer, I know these educated and dedicated people are there to help the public with their horticultural questions. Here’s a fact sheet from the Illinois University Extension regarding cottony maple scale.
© Ilex Farrell – Midwestern Plant Girl