Field validation of TOMCAST modified to manage Septoria leaf spot on tomato in the central-west region of Brazil

Abstract

Septoria leaf spot, caused by Septoria lycopersici, is a devastating disease on tomato in Brazil. In order to rationalize the chemical control, we validated the TOMCAST system to manage Septoria leaf spot on fresh market tomato in the State of Goiás, Brazil. Three field experiments were performed in a randomized complete block with five treatments and four replications. The first experiment was carried out from October 2017 to February 2018, the second from October 2018 to February 2019, and the third from November 2018 to March 2019. The treatments evaluated were: 1. Weekly calendar application of fungicides (WCA); 2 to 4. Disease severity values (DSV) 15, 20, and 25; 5. Control: plants not treated with fungicides. The values of the average air temperature and leaf wetness were used to calculate the DSV. The environmental conditions were favorable to the disease in experiments. The lowest values of the area under the disease progress curve (AUDPC) were recorded in WCA (809), DSV 20 (837), and DSV 15 (842) in the first experiment. Disease rates (r) of 0.010 were estimated in these treatments. Highest AUDPC (1325) and r (0.013) were detected in the control. In the second and third experiments, the highest AUDPC values were 638 and 59 in the control, respectively. The lowest AUDPC values were recorded in DSV 15 and WCA which were 325 and 28, 349 and 26, in the second and third experiments, respectively. No differences of r were detected in the second and third experiments. The highest number of fruits by plant (15) was estimated in DSV 15 in the second experiment. There were no differences on tomato yield in other experiments. As the number of fungicides applications was the highest in DSV 15, the TOMCAST system is not a useful tool for controlling Septoria leaf spot on tomato in the State of Goiás and other Brazilian regions with similar climatic characteristics.