The influence of growth stage of weeds on the glyphosate dose needed

摘要

Three distinct growth stages of black nightshade and couch grass were treated with eight different glyphosate rates. Black nightshade was treated at the 3-4, 5-6 and 9-10 leaf stage and couch grass was treated at the 3-4, 5-6 and 7-9 leaf stage. Dose response relationships demonstrated that the ED_(50) for glyphosate was 7, 36 and 130 g ae/ha with black nightshade at the 3-4, 5-6 and 9-10 leaf stages, respectively. The ED_(50) (dose giving 50 % response) with couch grass was on average 18 g ae/ha and was fairly constant at the different growth stages investigated. Relevance of relative growth rate, absolute fresh weight, spray retention and species-dependence is discussed.