Cottony Maple Scale

Cottony Maple Scale - a soft scale, is common on maple, honeylocust, linden and some other hardwood trees.

Cottony Maple Scale on tree branch
Photo: Southern Forest Insect Work Conference
Through: Forestry Images

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. In early summer, the scale resembling a marshmallow-like knob, which is the egg sack, is easily seen on twigs and small branches. A black mold called sooty mold typically grows on the sugary excrement from soft scales, aphids, and some other phloem (sap) feeding insects. Tree limbs, the trunk, and concrete or rock below the tree that have a black appearance, from the sooty mold, indicates the tree above is infested with soft scales, aphids, or other phloem feeding insects. Use the same insecticides mentioned for controlling oystershell scale during the crawler stage for the cottony maple scale, which is from early June through August.

Dormant oil spray can be applied only while the leaves are not on the tree. Some horticultural oils are available for use when the tree is in leaf, check the label carefully for application times. The horticultural oils act by smothering the scale insect, either in the egg stage or the crawler stage. Soil applications of systemic insecticides, applied commercially, eliminate the need to find a calm day to spray. Soil applications of systemic insecticides are taken up by the roots and translocated throughout the tree. As the insect feeds on the tree, they ingest the insecticide - killing them. Systemic insecticides can also be commercially applied into the water translocation cells in the tree trunk. Trunk injections work faster than soil injections and don't pollute the air and soil, but they do injure the tree trunk during the application process. Systemic insecticides applied in the soil or in the trunk provide a benefit by not affecting beneficial insects. Insecticides applied by spray can kill beneficial insects and require a thorough coverage of the tree to be effective. Trees can naturally ward off a harmful insect attack to some extent by being healthy. Sometimes an insecticide application may be required to save the tree.

Colorado State University Cooperative Extension

University of Wyoming - Cooperative Extension Service, publication B-1035 is particularly helpful for tree care. This online publication contains information on: Aphids, Borers, Cottonwood blotch leaf miners, Cytospora canker, Fireblight, Gall makers, Aspen leaf spots, Oystershell scale, Pear slugs, Powdery mildew, and Spider mites.