Binomial sequential sampling of Rhopalosiphum padi in winter wheat in the Southern Plains

Rhopalosiphum padi L. (Homoptera: Aphididae) population intensity (number p er tiller) was estimated on 99 occasions in hard red winter wheat fields th roughout Oklahoma from 1997-1999. We investigated the relationship between the mean number of R. padi per tiller (m) and the proportion of infested ti llers (PT). Over a wide range of plant growth stages, the P-T-m linear mode l provided a strong fit for data on R. padi at tally thresholds (T) of 0, 1 , 2, 3, 4, and 5. A regression model with a tally threshold of T-0 was the most precise for classifying R. padi populations during growth of winter wh eat because it explained 97% of the variation in the P-T-m relationship. Th e parameters of this model were significantly different from those of previ ously published models, suggesting the need for a separate sampling plan fo r R. padi in winter wheat in the Southern Plains. Sequential sampling stop lines based on sequential probability ratio tests were calculated for econo mic thresholds (ET) of 3, 9, and 15 R. padi per tiller at a tally threshold of T = 0. With P-0 and P-1 equal to the proportions of tillers infested co rresponding to +/- 0.167% of ET, and alpha and beta error rates set at 0.1, the average sample number required to reach a decision on R. padi populati ons varied from 112 (ET = 9) to 160 (ET = 15).