Development and validation of a binomial sequential sampling plan for the greenbug (Homoptera : Aphididae) infesting winter wheat in the southern plains

From 1997 to 1999, Schizaphis gramintum (Rondani), intensity (number per ti ller) was estimated on 115 occasions from hard red winter wheat fields loca ted throughout the major wheat growing regions of Oklahoma. A total of 32 a nd 83 fields was sampled during the fall and spring, respectively. The para meters of linear regressions relating the mean number of greenbugs per till er (m) and the proportion of infested tillers (P-T) differed significantly between fall and spring infestations. The P-T - m linear model provided a g ood fit for data on S. graminum for fall and spring infestations at tally t hresholds of 0, 1, 2, and 3. A tally threshold (T) represents the number of greenbugs present on a tiller before the tiller is classified as infested by >T greenbugs. A regression model with a tally threshold of 2 was the mos t precise for classifying S, graminum populations during fall growth of win ter wheat because it explained a greater amount of the variation in the P-T - m relationship (97%) than models with other tally thresholds. A separate spring model with a tally threshold of 1 was the most precise for classify ing S. graminum populations during spring growth of winter wheat. Sequentia l sampling stop lines based on sequential probability ratio tests were calc ulated for economic thresholds of 3 or 6 greenbugs per tiller for fall infe stations and 6 or 9 greenbugs per tiller for spring infestations. With the newly developed parameters, the average sample number required to classify greenbug populations near economic thresholds las above or below the econom ic threshold) varied from 69 to 207. We expect that the sampling plans for greenbugs in winter wheat developed during this study will be efficient and useful tools for consultants and producers in the southern plains.