ABSTRACT
Botrytis leaf blight of onion, caused by Botrytis squamosa, is controlled by foliar spraying with fungicides following a fixed schedule, without considering the progress of the disease. A spraying regimen based on a forecasting system can predict the disease progress, allowing a reduction in the number of sprayings and maximizing the disease control. Spraying programs were established based on the system of Marcuzzo & Haveroth with estimated accumulated severity values (ES) of 0.20, 0.25, and 0.30, compared to standard control programs (application intervals of 5 and 7 days) in 2017 and 2018 growing seasons. To assess the progress of botrytis leaf blight under the different spraying regimens, the statistical modeling technique known as mixed models was applied. These models include not only the fixed effects, but also the random effects for each individual in the study population. The accumulated severity of botrytis leaf blight as a function of time, for the five spraying programs, was calibrated with a Gompertz model adjusted by the mixed model and the random effect was adjusted to the upper asymptote. This parameter represents the disease severity potential for each treatment. As the result of the model calibration, the treatment with spraying regimen of ES=0.30 with three and four sprayings each year did not differ in control and yield from the conventional system used by the farmer with the advantage of reducing the number of sprayings and showing the same control efficiency.
Keywords
Allium cepa; Botrytis squamosa; epidemiology; chemical control
