Distribution of oak pit scale and associated crown dieback of Oregon white oak in Washington

Oak pit scale (OPS) infestations have caused dieback and occasional mortality of Oregon white oak (Quercus garryana) in the Columbia River Gorge area of Washington in recent years. In 2013, the Washington Department of Natural Resources conducted a survey of OPS populations and damage throughout the range of Q. garryana in Washington. Over 1,100 branches were collected at 37 plots from the San Juan Islands to Klickitat County and examined for OPS populations; their presence was confirmed in 92% of the plots. The majority of infested plots (79%) had low populations of OPS; from one to ten individuals per 30 cm branch length, on average. OPS populations tended to be higher at sites east of the Cascade Mountains. The golden oak scale, Asterodiaspis variolosa (Ratzeburg), was the only species of OPS identified in the survey. Signs of parasitoid emergence from OPS were present in 79% of infested plots. In 85% of plots with signs of parasitism, it was evident on fewer than half of infested branches. Crown symptoms of OPS are branch tip dieback paired with foliage that appears clumped due to epicormic shoot growth and delayed leaf expansion. These symptoms were recorded in 38% of plots, the majority of which were east of the Cascade Mountains. Crown symptoms of OPS were recorded as far north as the San Juan Islands, but whole tree mortality was rare outside of Klickitat County.