Attempts to increase phytotoxicity of glyphosat e her bic ide through addition of acid and/or of ammonium sulphate to the spray solution have been promising. Addition of these substances optimize chemical properties of the herbicide spray, overcoming negative effects of high pH and of íons present in it. The objective of this research was to investigate the effect of sulphuric acid and/or of ammonium sulphate addition to herbicide spray, on the efficiency of glyphosate mixed in diluents with high pH and high salts content. Glyphosate treatments consisted of five rates (variables from 180 to 540 g/ha a.e.), diluted in distilled water, and also glyph osate at 270 g/h a a. e. mix ed in the mineral waters Fonte Azul and Fonte Ijuí. To this herbicide rate, it was added 0,5 1/ha of sulphuric acid and /or 2,5 kg/ha of ammonium sulphate, whose treatments were sprayed over oat plants. Herbicide toxicity was evaluated at 7, 17, and 27 days after applications. Results showed that oats was very susceptible to glyphosate action, even when applied at 270 g/ha, independent of water used or adjuvantes added. It is concluded that addition of sulphuric acid and/or of ammonium sulphate to spray solution do not increase herbicide activity of glyphosate.
Avena strigosa; pH; additive; sulfuric acid; Ammonium sulphate