3.2.1
INTERNET DELIVERY OF THE OKLAHOMA PECAN SCAB MODEL FOR SCHEDULING FUNGICIDE APPLICATIONS

S VON BROEMBSEN, JD CARLSON, GF DRIEVER and MW SMITH

DASNR, Oklahoma State University, Stillwater, OK 74078, USA

Background and objectives
Pecan scab caused by the fungus Cladosporium caryigenum is the most economically important disease of pecans. For the past several years, we have been studying how weather parameters such as ambient temperature and relative humidity can be used to predict scab development in pecan orchards. From these studies we developed a weather-based threshold model for deciding when to apply fungicides to control scab effectively. Our final objective was to present the model at an interactive web site on the internet which growers and grower advisors could access daily for current recommendations and weather information.

Materials and methods
The Oklahoma Pecan Scab Model uses weather data from the Oklahoma Mesonet system of 117 weather stations located throughout the state of Oklahoma. Temperature and relative humidity data are automatically radioed to a centralized computer; programs process this information daily using the model to produce outputs for each of the locations. The model's thresholds are based on the accumulation of hours of disease conducive weather, or scab hours, and on the assumption that disease should not exceed a rating of 3 on the Horsfall-Barratt scale[1]. A scab hour is defined as an hour in which the average relative humidity exceeds 90% and the average temperature exceeds 75 F. The model also calculates in a fourteen day protection period following any fungicide application.

Results and conclusions
During March 1997 the Oklahoma Pecan Scab Model was set up to operate from an Oklahoma State University web site: www.okstate.edu/~mesonet/scab/ Growers can obtain information specific for any location in Oklahoma by accessing the site and using a clickable map to select the location of interest. The site gives the number of scab hours that occurred for each of the last 28 days, the total number of accumulated scab hours for the last 14 unprotected days, and the thresholds in scab hours for both highly susceptible and moderately susceptible varieties. This information can then be used to decide when to apply fungicides. The web site also links to important information such as fungicide rates, susceptibility of pecan varieties, and other pecan management practices. We are continuing to test the model in the field to fine tune the thresholds for different levels of susceptibility and are expanding the information that can be accessed from the web site.

References
1. Horsfall, J.G. and R.W. Barratt. 1945. Phytopathology 35:655.