3.1.6
USE OF WEATHER DATA AND DISEASE RISK ASSESSMENT MODELS FOR INTEGRATED DISEASE MANAGEMENT IN CALIFORNIA: BOTRYTIS CINEREA ON GRAPES AND STRAWBERRIES

JC BROOME1, WD GUBLER2, AC BORDAS2 and JF STRAND3

1Sustainable Agriculture Research and Education Program; 2Department of Plant Pathology; 3State-wide Integrated Pest Management Project, University of California, Davis, CA 95616, USA

Background and objectives
Over the past 15 years numerous models have been developed that quantify the influence of the environment and biological factors on disease. In California by 1997, several public and private weather station networks have been established with over 500 stations. These on-site weather stations monitor microclimate variables such as air temperature, relative humidity, hours of free moisture, and precipitation. The networks provide the infrastructure needed to collect appropriate weather data, facilitate research and validation of disease models, demonstrate use of models in disease management, and further region specific implementation efforts. Weather data and disease risk indices are gathered, controlled for quality, made available for users, and archived. A disease model database has been created as part of the University of California’s public weather station and disease forecasting network. This database contains descriptions of the available models, author(s), appropriate publications, algorithms, action thresholds and related disease management information, and model validation work performed in California. Botrytis bunch rot of grapes (Botrytis cinerea) is one disease that is described in the database. Broome et al. [1] developed a multiple regression model for predicting B. cinerea infection periods of grapes based on the interaction of the hours of free moisture and temperature. This model was validated on table grapes in Chile and is currently used extensively to time fungicide applications.

Results and conclusions
By the end of 1998, the disease model database will contain at least 41 different models of 13 important fruit and nut diseases in California, and 23 different models of 11 important vegetable and turf diseases. Currently, 20 disease risk models are being either developed, validated or implemented in California by different researchers. In California, between 1995 and 1997, the grape Botrytis model was evaluated for use on strawberries in Watsonville [2]. The action threshold was lowered for use on strawberries. Applications of iprodione were made according to the model versus a growers' standard program and resulted in 2 versus 4 applications in 1995, 4 versus 10 applications in 1996, and 8 versus 9 applications in 1997. Yields of marketable fruit were not statistically different in 1995, 1996 or 1997 between strawberries treated according to the model and those treated according to the grower's standard program. Fruit yields in plots treated with iprodione, either according to the model or the grower's standard timing, were significantly higher than in the untreated controls in 1995 and 1996, but not in 1997. In 1998, the model will be further evaluated and the action threshold fine-tuned at four locations along California's central coast.

References
1. Bordas AC, Gubler WD, 1997. Phytopathology 87, s10 (abstract). 2. Broome JC, English JT, Marois JJ et al., 1995. Phytopathology 85, 97-102.