Fungicides associated or not with phosphite for controlling glomerella leaf spot on apple

Abstract

The aim of study was to test fungicides and their association with potassium phosphite in reduction of glomerella leaf spot (GLS) and plant defoliation and select a grown model of the temporal progress of GLS in untreated plants during November and April, 2004/05 and 2005/06 seasons. The  experimental design was random blocks with four replications and the applications at intervals of 10 days. Evaluations of incidence, severity and  defoliation took place every 15 days (two branches per treatment). The fungicides evaluated were: mancozeb, chlorothalonil, methyl tiophanate, and
potassium phosphite (00-20-20). Analysis of variance was performed and mean comparison between treatments, and models were adjusted to describe the epidemic, compared themselves through Akaike information criteria (AIC). Methyl tiophanate showed efficient in defoliation reduction, but it did not reduce the area under progress curve (AUPC) for incidence and severity. Association of phosphite with methyl tiophanate reduced the AUPC of incidence and severity. During 2005/06 season the fungicide chlorothalonil was better than standard mancozeb, reducing the AUPC of incidence and severity. Adjustments of models are similar (R² >0.85 and similar values of AIC); the logistic model had the better epidemic adjustment.