PREDICTIVE MODEL FOR MAL-DE-RIO-CUARTO-DISEASE INTENSITY

''Mal de Rio Cuarto'' (MRC) virus disease is the most important virus disease of maize (Zea mays L.) in Argentina with the rural areas near Chajan, Sampacho, and Suco (in Rio Cuarto, province of Cordoba) being the most affected. A predictive model for MRC before planting a crop w as developed based on the disease intensity over nine agricultural yea rs (1981-82 to 1989-90) and a series of weather variables for that per iod (such as minimum, mean, and maximum temperatures, number of frosts , and amount of rainfall). To build the model, agricultural years were divided into two groups according to the percentage of severely affec ted plants (intensity). A year was considered ''mild'' if the percenta ge of severely affected plants was less than 20% and ''severe'' if the percentage was higher. A discriminant stepwise procedure was used to analyze data. The average maximum temperatures in June, July, and Augu st, the average maximum temperatures in July and August, and the total rainfall in June, July, and August were found to be significant forec asters of disease intensity. The model was validated in the agricultur al years of 1990-91, 1991-92, 1992-93, and 1993-94. The relative inten sity of the disease was adequately forecasted and confirmed for those years. Results support the feasibility of forecasting MRC intensity pr ior to planting maize in the area under study.