Resumo

ARREGUI, M. Cristina; SCOTTA, R. Ricardo  e  SANCHEZ, D. Eusebio. Chemical fallow phytotoxicity on wheat and maize. Agrociencia [online]. 2009, vol.43, n.6, pp.595-601. ISSN 2521-9766.

In direct seeding - the prevailing management system for wheat and maize in the Argentine humid pampas - crops are set without turning over the soil and by using chemical fallow. This technique allows to preserve the soil water content during plantation. When mixtures of glyphosate with 2, 4-D or metsulfuron methyl have been applied to control weeds, some phytotoxical effects have been observed. The objective of this study was to evaluate the phytotoxicity produced by mixtures of glyphosate and metsulfuron methyl or 2,4-D on wheat and maize. In 2002 and 2003, both crops were sown in manually weeded experimental plots. The experimental design consisted of split plot with three replicates, where the date of application was the main plot: 50 and 24 d before sowing for wheat and 30 and 15 d before that of maize. The sub-plots were the mixtures of glyphosate (1.44 kg ha^-1 of i.a.) with 2,4-D (250 and 500 g ha^-1 a.i.) for both crops, and metsulfuron methyl (3 and 6 g ha^-1 a.i.) for wheat. Phytotoxicity symptoms were detected and height was analyzed at different growth stages as well as grain yields. In wheat there was chlorosis and reduced height (p<0.05) with high doses of 2,4-D and metsulfuron. With abundant rainfall, metsulfuron at a dose of 6 g ha ^-1 and 2,4-D at a 500 g ha^-1 dose caused a reduction of yield (p<0.05). In maize, both doses of 2,4-D affected height (p<0.05), especially when 500 g ha^-1 were applied 15 d before sowing, but yield was only affected when rainfall was excessive (p<0.05). The analysis of results suggest that fallow with metsulfuron methyl and 2,4-D on wheat and maize causes phytotoxicity when using high rates or if there is proximity between application and sowing under excessive rainfall.

Palavras-chave : Glyphosate; metsulfuron methyl; 2,4-D; direct seeding.

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