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Golden Oak Scale

July 3, 2007

Golden oak scale crawlers have been reported in northeastern Illinois. Golden oak scale has been found in that area of the state for several years, particularly in nurseries on white oak. The insect attacks a variety of white and black oak group species.

Golden oak scale is a pit scale, meaning that the scale occurs in the center of a pit in the bark that is about 1/8 inch in diameter and up to half that deep. In the center of the pit is a gold-colored, round, white, waxy-fringed female scale up to the size of a pinhead. The pit is thought to be caused by the removal of fluids or the injection of toxins by the scale that keeps that portion from growing as much as the surrounding tissue.

Crawlers, young newly hatched scales, are produced in the late spring to early summer and continue to be produced for about 5 months. The crawlers typically do not crawl far and tend to settle down to feed primarily on 1-year-old and the current year’s growth. Mature females overwinter. There is one generation per year.

Untreated trees can experience reduced growth and dieback of young twigs. Damage typically appears in late summer and fall. Dead twigs tend to hang onto their dead leaves, making them obvious during the winter on deciduous oaks. Infested trees tend to leaf out about 3 weeks later in the spring. Young trees can be killed. Infested trees tend to have more anthracnose than those not infested. The combination of scale and anthracnose can kill even established trees.

Treatment is aimed at the crawler stage. Dormant oil sprays and other applications against the mature female scales are relatively ineffective. Spray the crawlers at this time with acephate (Orthene), bifenthrin (Onyx, Talstar), or cyfluthrin (Tempo). Check for crawlers a month after spraying and retreat if crawlers are present.

(Phil Nixon and Kathy Sharpe)