Frequência e época de aplicação de fungicidas e seus efeitos em híbridos de milho (Zea mays L.)

Abstract

Among the major diseases with potential for reducing the final yield of maize (Zea mays) are common rust (Puccinia sorghi), and Spot Blotch (Exserohilum turcicum). Seed companies offer hybrids with levels of disease resistance in the shoots, however, these have demonstrated the need for alternatives that help to maintain the low rate progress of diseases. Given the potential of triazole and strobilurin disease control in the culture and the need to integrate control practices, this study evaluated the effects of times and frequency of application of mixtures of triazoles + esbrubilurinas in hybrids with different levels of resistance. Through two experiments in 2007/2008 and 2009/2010 seasons, the experimental design was randomized block in factorial arrangement (3x4x3) with four replications. In a total of two experiments were used four hybrids; Pioneer 32R21, Pioneer 32R48 and 32R22 and Pioneer NK Penta; three fungicides, azoxystrobin + Ciproconazol (at 200 g/L + 80 g/L + Mineral oil 0.5% v / v) + Pyraclostrobin Epoxiconazol (at 133 g/L + 50 g/L), + picoxystrobin Ciproconazol (at 200 g/L + 80 g/L + Mineral oil 0.5% v / v) at doses of 0.3 L/ha, 0.75 L/ha and 0.3 L/ha respectively, plus a control without fungicide. The fungicides were applied in three application programs: at the time of seven leaves fully exposed, at tasseling and combination between the two periods, 7 sheets + tassel. The variables were the AUDPC for rust and leaf spots calculated from four disease severity, grain weight, grain yield and rate of SPAD. It was found that triazole + strobilurin have a suppressive effect on the AUDPC of disease. Also there was significant correlation between SPAD index, grain weight and grain yield, being indicative of a physiological effect that contributes to the grain weight and the final yield.