ABSTRACT
Onion downy mildew is controlled by means of foliar spraying with pesticides following a fixed schedule, without considering the disease progress. A spraying regime based on a forecasting system can predict the disease progress, consequently reducing de number of sprayings and maximizing the disease control. Spraying regimes were based on Wallin system (1962) with accumulated severity values (VDS) of 6, 8, 10 and 12, compared to the standard control (application interval of 5 and 7 days) in 2014 and 2015 growing seasons. With the aim of assessing downy mildew progress under different spraying regimes, the statistical modeling technique known as mixed models was applied. These models include not only fixed effects, but also random effects for each of the individuals in the study population. The accumulated severity of downy mildew as a function of time, in the six spraying regimes, was calibrated with a Gompertz model adjusted by the mixed model and the random effect adjusted to the upper asymptote. This parameter represents the disease severity potential for each one of the treatments. As the result of the model calibration, treatment with VDS 12 spraying regime of seven sprayings in both years did not differ in the control and in the 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; epidemiology; chemical control
