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Evaluation of FAST as a Forecasting System for Scheduling Fungicide Sprays for Control of Stemphylium vesicarium on Pear. E. Montesinos, Department of Crop Sciences, Technical University of Catalunya, Avda. Lluís Santaló, s/n, 17003 Girona, Spain. P. Vilardell, Mas Badia Agricultural Experiment Station, La Tallada, Girona, Spain. Plant Dis. 76:1221-1226. Accepted for publication 11 June 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-1221.

The influences of temperature on mycelial growth and of temperature and relative humidity on germination of conidiospores were studied in six strains of Stemphylium vesicarium isolated from lesions on pear fruit (Pyrus communis) grown in areas of Catalunya, Spain. Optimal temperatures were 15–25 C for mycelial growth and 20–30 C for germination of conidia. Conidia germinated only when relative humidity ranged from 98 to 100% and free moisture encompassed the conidia. Comparison of these data with weather parameters during epidemics indicated that under climatic conditions in Spain, the principal limiting factor for epidemic development is duration of wetness. The FAST model developed for forecasting of early blight on tomato was evaluated in relation to its accuracy for predicting infection periods of pear fruit spotting and its usefulness in scheduling fungicide sprays for control of this disease. Trees were monitored from May to October in 1989, 1990, and 1991. Final disease incidence at harvest, after 4-wk exposure periods to natural inoculum when trees were not sprayed, revealed periods of infection that coincided with those predicted by the FAST model to favor disease development. Fungicide applications scheduled by FAST limited the development of pear fruit spotting to the same level achieved with the commonly followed 7-day commercial schedule but with 28% fewer fungicide applications in moderately diseased orchards.