Pest description and damage The sycamore scale is tiny. This insect causes leaves to develop small yellow spots. Eventually, the leaves become pock-marked with numerous small, brown, necrotic (dead) spots that may be confused with leaf spot fungi. Leaves infested while young are often smaller and disfigured. Premature leaf fall also may occur, although other factors may cause early leaf drop. Scale also feed on bark, causing twig dieback.
Biology and life history The scale overwinter in crevices on the bark. Eggs are laid in late winter in cottony masses. Egg hatching coincides with leaf budbreak and continues until the leaves are fully expanded. The crawlers move from the bark to the new foliage to feed. Sycamore scale frequently align themselves along the major veins of the leaf to feed. They remain here until maturity, and then migrate back to the bark to lay eggs for a new generation. There may be three to five generations per year.
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