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Ecology and Epidemiology

Modeling of Superimposed Spatial Patterns of Bacterial Brown Spot of Snap Bean. B. D. Hudelson,Department of Plant Pathology, University of Wisconsin, Madison 53706; M. K. Clayton(2), K. P. Smith(3), and C. D. Upper(4). (2)Department of Plant Pathology, Statistics, University of Wisconsin, Madison 53706; (3)Department of Plant Pathology, University of Wisconsin, Madison 53706; (4)Department of Plant Pathology, Agricultural Research Service, U. S. Department of Agriculture, University of Wisconsin, Madison 53706. Phytopathology 83:430-438. Accepted for publication 15 December 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/Phyto-83-430.

Snap bean plants within seven-row segments that ranged from 30 to 108 m were sampled using a 2,4-systematic sampling plan: Two adjacent plants were sampled and evaluated for bacterial brown spot, four adjacent plants were skipped, two adjacent plants were sampled, etc. This sampling plan was developed using a priori knowledge of disease patterns in 5-m row segments. Every leaflet on every sampled plant was assessed for bacterial brown spot, and disease on these plants was quantified as the proportion of diseased leaflets per plant. Arcsine square root-transformed disease-incidence values were analyzed for spatial patterns using auto-regressive integrated moving average (ARIMA) modeling. Three of seven data sets were described by a generalized ARIMA(1 0 1) model. These data sets exhibited the expected patterns of disease, based on previous descriptions of disease patterns in 5-m row segments. Of the remaining four data sets, one was modeled by an ARIMA(1 0 2) model, two by an ARIMA(1 0 3) model, and one by an ARIMA(1 0 4) model. These data sets exhibited the expected patterns, as well as additional patterns that recurred at intervals of six to 11, 12 to 17, or 18 to 23 plants, respectively. Significant autocorrelations at distances of six to 23 plants were also found in residuals from 24 of 55 5-m row segments evaluated for bacterial brown spot and modeled using ARIMA models. These patterns appear to occur frequently in commercial snap bean fields.