THE INFLUENCE OF TEMPERATURE AND RELATIVE-HUMIDITY ON THE EFFICACY OF GLUFOSINATE-AMMONIUM

The influence of temperature and relative humidity (r.h.) on the efficacy of glufosinate-ammonium was investigated in controlled-environment growth chambers using a tolerant species, barley (Hordeum vulgare L. cv. 'Samson'), and a susceptible species, green foxtail (Setaria viridis (L.) Beauv.). The shoot ammonia concentration and visual injury of plants treated with glufosinate-ammonium doses of 100 and 800 g ha-1 were compared at day/night temperature regimes of 8/5, 15/10 and 22/17-degrees-C at 60% r.h. The effect of relative humidity levels of 40% and 95% on the shoot ammonia concentration, visual injury and dry weight accumulation of glufosinate-ammonium-treated plants was tested at temperature regimes of 15/10 and 22/17-degrees-C, with both species treated with 800 g ha-1. In addition, green foxtail treated with 100 g ha-1 was tested at both r.h. levels at 22/17-degrees-C. As the temperature decreased, less ammonia was produced in treated green foxtail plants. However, ammonia levels were comparable at all temperature regimes for barley. Lowest temperatures resulted in delayed injury to both species, but only small differences in injury existed among temperature regimes 288 h after spraying. The activity of glufosinate-ammonium on both species was significantly decreased by low r.h. For example, when grown at 22/17-degrees-C, green foxtail survived the potentially lethal dose of 100 g ha-1 at 40% r.h. and accumulated 70% of the dry weight of control plants, but was killed at 95% r.h. Of the two environmental factors examined, r.h. had the most significant effect on the phytotoxic action of glufosinate-ammonium.