Scale Insects
From Bugwoodwiki
Contents |
Importance
Scale insects reduce plant vigor and may cause faded areas in affected leaves, premature leaf drop, and even twig mortality. They produce honeydew, which supports the growth of sooty molds that block photosynthesis. Injuries detract from the appearance and value of the tree. These insects occur throughout the United States.
Identifying the Insect
Terrapin scale females appear as oval-shaped, reddish-brown, shiny bumps (2 mm across) on branches (fig. 13a). Cottony maple scale females look like small powdery popcorn kernels with a dark shell (4 to 6 mm) trailing a large cottony white egg sac (fig. 13b). European fruit lecanium females are distinctly humped (3 to 6 mm), dark brown to reddish, and sometimes covered with whitish powder (fig. 13c). Oystershell scale females look like tiny (3 mm long), chestnut-brown oyster shells. In large numbers they form a “crust” on trunks and branches.
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| Figure 13a. - Terrapin scale |
Identifying the Injury
Injury may appear as yellow spots on leaves, necrotic areas, dieback, shiny leaves, growth of black sooty mold, or leaf drop. Scales can be found by examining the bark.
Biology
Scale insect life cycles are complicated with large, somewhat sedentary females and relatively small, winged males. There may be several generations per year. Overwintering is typically on branches or under bark.
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| Figure 13b. - Cottony maple Scale |
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| Figure 13c. - European fruit lecanium |
Control
Parasites and predators usually keep scales under control. Occasional chemical treatment of ornamental plants may be useful.
References
Leininger, T.D; Solomon, J.D.; Wilson, A. Dan; Schiff, N.M. 1999. A Guide to Major Insects, Diseases, Air Pollution Injury, and Chemical Injury of Sycamore. Gen. Tech. Rep. SRS-28. Asheville, NC: USDA Forest Service, Southern Research Station. 44 p.
