Grape mealybug, Pseudococcus maritimus (Ehrhorn) (Hemiptera: Pseudococcidae), is a pest of grape vines, Vitis vinifera (Vitales: Vitaceae) and a known vector of several strains of grapevine leafroll-associated virus. Seasonal increase and decline of Ps. maritimus populations on wine grapes is described in each of three important grape growing regions in Oregon using pheromonebaited traps and visual monitoring. Delta traps and genomic verification of collected sessile stages found that only Ps. maritimus is present in Oregon vineyards. Seasonal pheromone-baited trapping and visual surveys during 2010 and 2011 identified two population peaks for adult male flight and sessile developmental stages on vines in Southern Oregon and the Columbia Basin. Willamette Valley vineyards identified one peak male flight period using pheromone-baited traps but no sessile individuals were found in visual surveys. Seasonal developmental stages are described for Southern Oregon and the Columbia Basin. First instar stages generally were observed one month before peak male flight and were less abundant during peak flight. Adult females and late instar stages were found on vines at the peak of male flight. Pheromone monitoring identified the presence of mealybug populations in viticultural areas, even when intensive visual surveys were unable to do so.