Efficacy of post-emergence herbicides for weed control in chemical fallows in southern Queensland

Abstract

Out-of-patent herbicides (2,4-D, MCPA, dichlorprop, amitrole, ametryn, atrazine and linuron) were screened at 3 rates of post-emergence application for weed control during fallow periods in southern Queensland. Herbicide efficacy was assessed on 26 weeds at 1 or more stages of growth. Each herbicide had a limited spectrum of activity over the range of species encountered, with amitrole being the most effective. The chlorophenoxy compounds controlled only some of the broad-leaved species and had no effect on grass species. Where more than 1 growth stage for each weed was encountered, differences in susceptibility to the herbicides were evident amongst stages. Most herbicides were ineffective on large weeds. The rate of herbicide application also influenced the level of activity on most species. Most of the weeds in the Brassicaceae group were susceptible to all rates of the chlorophenoxy herbicides.