Presence—Absence Sequential Decision Plans for Tetranychus urticae (Acari: Tetranychidae) in Garden-seed Beans., Phaseolus vulgaris

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Abstract
A sequential decision plan was developed for assessing economic status of twospotted spider mites, Tetranychus urticae Koch, in garden-seed beans, Phaseolus vulgaris L. Precision and cost analyses showed that sample units should consist of single trifoliolate leaves picked from the bottom third of the plant canopy. Provisional economic thresholds were established for two preharvest intervals in terms of proportion of leaves infested with ≥5 mites and ≥10 mites per leaf. Upper and lower critical limits of the sequential decision plan were defined by the confidence interval: Ci = (P1)(n) ± (t)(n)[[[P1(l − P1)]/n]14], where Pt is the economic threshold, n is number of leaves examined, and t is the Student’s t statistic for the acceptable error level.