Home gardeners may notice small insects placing white tufts of cotton on their plants and trees. These insects are cottony maple scales, which are often found on a variety of ornamentals. While these pests are not harmful to healthy trees, they can damage trees weak or under stress.
Cottony maple scales are usually noticed when a large number of white, cottony bundles appear on host trees. These bundles are egg sacks, which are placed on the tree by the scale insect. Each white egg sack may contain over 1,500 eggs. Cottony maple scales are small and oval with a flattened shape. These insects are typically brown in color and do not have wings. Cottony maple scales attach themselves to host trees with their mouths, where they remain for their entire lives. Common hosts of cottony maple scales are red maple, silver maple, white ash, willow, oak, boxelder, euonymus, sycamore, hackberry, elm, beech, poplar, dogwood and basswood.
Infestations of cottony maple scales may be distressing for home gardeners for a variety of reasons. These pests excrete a sticky substance called honeydew after feeding on plant juices. This clear liquid drops onto plant leaves, cars, sidewalks and driveways and sticks there. Sooty mold fungi grow on honeydew, causing a black, crusty fungus wherever honeydew is present. Cottony maple scale infestations cause host trees to become unsightly because of the numerous white cotton egg sacks on trees and sooty mold. Trees infested with this scale insect may suffer from twig dieback and sometimes the entire tree dies.
A number of predatory insects feed on cottony maple scales, keeping their population levels low. Parasitic wasps, predatory mites and lady beetles feed on cottony maple scales. If beneficial insects are present and feeding on cottony maple scales, do not use insecticides, as these products kill the beneficial insects as well. Pruning branches heavily infested with egg sacks also helps reduce infestations.
Insecticidal soaps and horticultural oils are safe chemical products that will not kill beneficial insects. These products kill scales on contact. Systemic insecticides, such as soil drenches, treat cottony maple scale infestations. These products are delivered to insects through the plant roots, where they are transported throughout the plant and kills feeding scales.
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