Effect of Halosulfuron Rate and Application Timing on Volunteer Azuki Bean Control in White Bean

Abstract

Three field experiments were carried out during 2017-2019 at the University of Guelph Huron Research Station near Exeter, Ontario, Canada to determine the effect of halosulfuron rate (25, 37.5 or 50 g ∙ ai ∙ ha -1 ) and application timing (POST 1, POST 2 and POST 3) on volunteer azuki bean control in white bean. At POST 1, halosulfuron at 25, 37.5 and 50 g ∙ ai ∙ ha -1 controlled volunteer azuki bean 46% - 50% at 1 week after application (WAA), controlled decreased to 16% - 25% at 8 WAA. At POST 2, volunteer azuki bean controlled decreased from 34% - 39% at 1 WAA to 17% - 27% at 8 WAA. A similar trend was observed at POST 3. Halosulfuron applied POST 1 at 25, 37.5 and 50 g ∙ ai ∙ ha -1 reduced biomass 49%, 64% and 69%, respectively. Halosulfuron applied POST 2 did not reduce volunteer azuki bean biomass at 25 g ∙ ai ∙ ha -1 , but decreased biomass 51% at 37.5 g ∙ ai ∙ ha -1 and 49% at 50 g ∙ ai ∙ ha -1 . Similarly, halosulfuron applied POST 3 did not reduce volunteer azuki bean biomass at 25 g ∙ ai ∙ ha -1 , but decreased biomass 40% at 37.5 g ∙ ai ∙ ha -1 and 44% at 50 g ∙ ai ∙ ha -1 . There was as much as 19%, 22% and 25% dockage with halosulfuron applied POST 1, POST 2 and POST 3, respectively. Volunteer azuki bean interference reduced white bean yield 40%. Reduced volunteer azuki bean interference with halosulfuron applied POST 1 at 37.5 or 50 g ∙ ai ∙ ha -1 resulted in an increase in white bean yield relative to the weedy control; however white yield was less than the weed-free control. This study concludes that halosulfuron at rates and application timings evaluated does not provide adequate control of volunteer azuki bean in white bean.