Regression Sampling Plan for Twospotted Spider Mite (Acari: Tetranychidae) in Oregon Peppermint1

Abstract

A sampling plan for detecting aggregations of Tetranychus urticae Koch was developed to aid pest management decisions in peppermint, Mentha piperita L. Ten to 14 sites were sampled for every 74 ha. At each site, 45 leaves (15 top, 15 middle, 15 bottom) were evaluated for the presence of five or more T. urticae. The sample mean was estimated from the equation: log (x_bar + 1) = 0.18 + 0.59 log (INF5 + 1), which was based on the relationship between the mean density of mites (x_bar) and the number of leaves per sample with five or more mites present (INF5). The coefficient of determination for this relationship is 0.92. The equation provides an accurate estimate of mean mite densities over widely separated regions, during different growing seasons, and for fields with different mite densities.