We developed a binomial sequential decision plan that classifies the economic status of nonviruliferous pea aphids, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae), in commercial dry peas, Pisum sativum L. (Fabales: Fabaceae), in the Palouse region of northern Idaho and eastern Washington state. Relationships between mean pea aphid density per plant (x) and the proportion of aphid-infested plants (Pi) were determined by in situ visual counts of 100 plants on each of 27 seasonal dates during 2011 from early vegetative plant growth (stage V105) to late reproductive growth (stage R207) at two field sites near Moscow, ID. The best-fit Nachman model Pi = 1 - exp(-0.3616 x0.808) was used to restate the limits of noneconomic and economic infestations from one and three aphids per plant to 30 and 58% aphid-infested plants, respectively. Sequential decision plans were computed using the stop-line formulas of Waters for Wald's Sequential Probability Ratio Test. Validation of the sequential decision plan by simulated sampling from the 2011 data as well as from six commercial fields sampled during 2012 showed that when observed field densities either exceeded the economic injury level or were less than one third the economic injury level, the plan correctly classified aphid economic status in >99% of the resampling trials. Practical implementation of the plan is discussed.
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