Development of a threshold model for scheduling fungicide applications to control pecan scab

Scope and method of study. The purpose of this study was to develop a forecasting model for timing fungicide applications to control of pecan scab based on weather conditions conducive to disease progression. Initial studies were conducted to provide an understanding of the epidemiology of pecan scab on the unsprayed leaves and fruits of both native pecans and susceptible cultivars at several sites in Oklahoma. Weather data was monitored at each site. Weekly mean disease ratings were correlated with hourly accumulations of combined temperature and relative humidity data to produce forecasting models by both empirical and statistical methods. The empirical model was tested at two sites in 1996. The statistical model developed in 1996 was tested at one site in 1997. The model was programmed onto an interactive web page using the Oklahoma Mesonet Weather system as a source of weather data.;Findings and conclusions. The epidemiological studies clearly showed that susceptible cultivars develop higher levels of disease than most native pecan trees. Pecan fruits are more susceptible to disease than the leaves for all pecan trees. Empirically derived graphs comparing disease progression with the accumulation of combined temperature (21.1-29.4C) and relative humidity (...