ABSTRACT
Onion downy mildew can be controlled by foliar spraying with fungicides following a fixed schedule. The spraying regime based on a forecasting system can predict and minimize the disease progression. As the epidemiological behavior of this disease in southern Brazil is unknown, the present study aimed to analyze its temporal progress under different spraying regimes. A randomized block design and four replicates were used to evaluate the spraying regimes based on Wallin system (1962) with accumulated daily severity values (DSV) of 6, 8, 10 and 12, compared with standard control regimes (5- and 7-day application intervals). The disease severity was weekly evaluated in ten random plants previously demarcated in each replicate. The disease progress curve for each regime was adjusted to Gompertz model, since the observed severity corresponded to the model and was confirmed by the consistency between the estimated points and by the residue. The five-day regime had the highest progress rate (0.42338), while DSV 8 had the lowest one (0.30853). The regime with DSV 8 presented maximum severity, peaking at 41.5%, and the 5-day regime had the lowest disease accumulation, of 30.9%. The spraying regimes showed no difference in the temporal progress behavior of onion downy mildew. The use of this forecasting system has proven to be a viable tool for the management of onion downy mildew in Santa Catarina State, Brazil, and is available for the production chain at http://www.ciram.sc.gov.br/agroconnect/.
Keywords
Allium cepa
; oil spot; culture medium
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