PT - JOURNAL ARTICLE AU - A. H. Purcell TI - Spatial Patterns of Pierce's Disease in the Napa Valley AID - 10.5344/ajev.1974.25.3.162 DP - 1974 Jan 01 TA - American Journal of Enology and Viticulture PG - 162--167 VI - 25 IP - 3 4099 - http://www.ajevonline.org/content/25/3/162.short 4100 - http://www.ajevonline.org/content/25/3/162.full SO - Am J Enol Vitic.1974 Jan 01; 25 AB - The spatial pattern of Pierce's disease of grapevines was studiied by mapping diseased grapevines in eight vineyard plots in the Napa Valley, California. The percentage of diseased vines was highest nearest natural riparian vegetation, declining with distance (up to 400 to 500 ft) from natural source areas of the principal leafhopper vector, Hordnia circellata (Baker). The slope of disease dispersal gradients annual changes in apparent infection rate, and the overall incidence of Pierce's disease varied among grape varieties in adjacent plantings with similar exposure to vector source areas.