Difference in Response of Weeds to Effects of Hard Water on Glyphosate Efficacy

Water hardness antagonism and effect of ammonium sulfate on efficacy of glyphosate have been well documented. However conflicting answers between weed species were noted by the authers. Greenhouse studies were conducted in Ferdowsi University of Mashhad in a randomized complete block design with a factorial arrangement and three replications in two runs over 2014-2015. Four experiments were arranged separately on Kochia scoparia L., Amaranthus retroflexus, Phalaris minor, and Avena ludoviciana through ammonium sulfate in deionizad water and in the presence of different salts, include NaHCO3, CaCO3, MgCl2, CaCl2 (500 ppm), three doses of glyphosate (256.25, 512.5, 1025 and g a.e. ha-1), with and without ammonium sulfate as adjuvant (2% w/v). The results showed the application of AMS in overcoming the inhibitory effects of salts in the spray solution in tested species was different, So that in Amaranthus retroflexus was more than Avena ludoviciana and Phalaris minor . Glyphosate with AMS caused reduction in dry matter in grasses from 0.34 g to 0.28, while glyphosate toxicity in redroot pigweed with AMS was 100% and all of the plants were destroyed (0.82 to 0). The application of AMS in overcoming the inhibitory effects of hardness had no effect on control of Kochia scoparia. Therefore weed species should be considerate in hardwater for optimum glyphosate efficacy.

کلیدواژه ها:

Kochia scoparia L. ، Calcium ، Glyphosate ، Hard water ، Magnesium