Evaluation of a predictor system for Septoria leaf spot in staked tomato plants in Caçador, SC, Brazil

Septoria leaf spot, caused by the fungus Septoria lycopersici, is one of the most important diseases of staked tomato in Caçador, Santa Catarina State, Brazil. The disease is used to be controlled by preventive fungicide applications. Field experiments were carried out to evaluate disease predictors based on TomCast model (10, 15, and 20 disease severity value - DSV) or by a leaf wetness period (≥12 h). The TomCast utilizes the duration of leaf wetness and average temperature during the wetness period to calculate a daily severity value (DSV). Both systems were compared to weekly calendar application schedules. There was no significant difference among the predictors and the weekly schedule methods of disease control with regards to the yields, final disease severity, area under the disease progress curve and the apparent infection rate (r). However, the 20VSD predictor reduced fungicide applications by 12.5 to 70% compared to the scheduled weekly sprays.