To help preserve the vitality of our urban forest, the Village of Niles has again taken steps to control Cottony Maple Scale and the Honeylocust Plant Bug on parkway trees. In the past the one pest that has been especially abundant in northeastern Illinois is the soft scale insect known as the Cottony Maple Scale, shown to the right.
Village of Niles Superintendent of Public Works Fred Braun said, “Usually the first sign of Cottony Maple Scale is a sticky sap-like substance on car windows. Soft scales produce "honeydew" which is actually a sugary excrement that gets on car windows and anything else under the tree.” Braun added, “Another negative of honeydew production is that it attracts ants and wasps to the area and also coats the leaves, which promotes the growth of black, sooty mold fungi.”
In the overwintering stage, the insect is oval, flat and pale to dark brown without obvious legs, antennae or wings. Later, a white cottony egg sac two to three times the length of the scale is produced in the spring. Braun said this gives the appearance of cotton balls being strung from twigs as shown in the above picture.
Overwintering females complete development in June and lay eggs through late summer. Each cottony white egg mass contains 1,000 to 1,500 eggs. Eggs hatch into crawlers in late June through July. The crawlers are flat, oval, brown insects with two distinct eyes, short antennae, tiny legs and are microscopic, or about the size of a period on this page. They migrate to the underside of leaves and insert their piercing-sucking mouthparts along the midrib and then withdraw sap from the tree’s vascular cells. They spend the remainder of the summer feeding on leaves.
Males mature in late summer, emerge as tiny, winged gnat like insects, mate with immature females and then die. Just before leaf drop, mated females move back to the branches and twigs and reinsert their mouthparts for overwintering. There is one generation a year.
Superintendent Braun said, “The insect feeding causes twig dieback and severe infestations can even kill major limbs and occasionally the entire tree, especially if the tree is stressed due to dry weather, and is why we take preventative steps to control Cottony Maple Scale.”
The Village of Niles has hired Autumn Tree Care to spray affected trees with a refined dormant oil before bud break to control the scale. Braun added, “While other trees may be infested, silver maple trees are its favorite host in Niles.” Work will begin on March 20th (weather permitting), and should be completed by the end of the month.
This same treatment also helps stop the Honeylocust Plant Bug, which is a pest that feeds on new leaves of Honeylocust trees. For the Honeylocust Plant Bug, both the nymph and adult pest feed on the foliage of the plant, although the most serious damage is caused by the nymph, early in the season said Braun.
Damage can include severe leaf distortion, discoloration and dwarfed leaflets. Severe defoliation weakens the tree and increases its susceptibility to invasion by secondary insect and disease pests. Complete defoliation of the host plant is possible.
Overall the Village of Niles will treat approximately 3,000 parkway trees. For further information about this program you may contact the Niles Forestry Division at 847-588-7900.