Investigation on the influence of spray tank water quality on glyphosate performance and eliminate the adverse effects

The influence of water quality on glyphosate and nicosulfuron performance on barnyard-grass and velvetleaf was examined in a greenhouse study as a factorial arrangement of treatments based on a completely randomized design with 6 replications at Ferdowsi University during 2008-9. Factors included were: pH at 8 levels (3, 4, 5, 6, 7, 8, 9, and 10) obtained by using buffer solutions (+3 control pots for each pH level), CaCO3 at 6 levels (0, 100, 200, 300, 400, 500, and 600 ppm (w/v)) in combination with 0 or 3 kg/ha (NH4)2SO4 (AMS), and NaHCO3 at 6 levels (0, 100, 200, 300, 400, 500, and 600 ppm (w/v)) in combination with 0 or 0.5 L/ha NH4NO3 (AMN). The herbicide solutions were applied at the 3-4 leaf stage of the weeds at the ED50 doses estimated in a dose-response preliminary test (158 g ai/ha). The results showed that glyphosate at pH of 6 and 7 had the highest effect on barnyard-grass, similarly, the best control of velvetleaf was obtained by glyphosate at a pH of 6 that there was no significant difference between pH 7. The antagonistic effects of CaCO3 (hardness factor) and NaHCO3 (alkalinity factor) on glyphosate spray tank reduced significantly its efficiency. However, adding AMS and AMN to the spray tank decreased the adverse effects of water hardness and alkalinity, respectively, therefore improved the glyphosate performance on barnyardgrass and velvetleaf control. However, the effect of addition of AMS and AMN to the soluble herbicide for control of velvetleaf was evident over the barnyardgrass. In conclusion, the results of these experiments have highlighted the importance of water quality on glyphosate performance.