Oak lecanium, Parthenolecanium quercifex (Hemiptera: Coccidae), is a common soft scale insect pest of oak trees and other woody plants. They infest trees under high stress, such as those planted in parking lots, greenscapes, and other urban areas. Like other soft scale insects, oak lecanium scales feed on tree sap, and they excrete the excess sugars as honeydew. Sooty mold fungus grows on honeydew, and its black color blocks sunlight and interrupts photosynthesis. Although lecanium scales have little immediate impact on twigs and branches, extensive infestation and subsequent feeding damage may weaken or kill the tree over time. The problems with lecanium scale are worsened in urban landscapes where local temperatures are generally higher. Higher temperatures decrease the relative number of parasites that feed on scale insects, and the high densities of surviving females continue to produce viable eggs.
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Published on Oct 23, 2023