Characterization of Fluazifop-P-butyl Activity on Bristly Starbur (Acanthospermum hispidum)

Abstract

During routine use of fluazifop-P-butyl for grass control, county extension agents in Georgia observed control of bristly starbur in grower fields. Experiments to characterize the activity of fluazifop-P-butyl on bristly starbur were conducted under greenhouse conditions in Gainesville, FL, during 2001 and 2002. Fluazifop-P-butyl activity was characterized as a function of herbicide rate and time after application. Commercially available fluazifop-P-butyl was compared to technical fluazifop-P-butyl as a function of herbicide rate and bristly starbur height. Finally, injury to bristly starbur was evaluated when clethodim, diclofop, fluazifop-P-butyl, haloxyfop, quizalofop-p, and sethoxydim were applied at two growth stages. Fluazifop-P-butyl caused >90% injury to bristly starbur with all other post graminicides displaying <8% injury. Nonlinear regression revealed a sigmoidal response of bristly starbur injury to fluazifop-P-butyl. Estimates for 50 and 90% bristly starbur injury (I50and I90) were 0.07 and 0.14 kg ai/ha, respectively. There was no difference in activity of technical and commercial fluazifop-P-butyl formulations. There was a differential response of bristly starbur to fluazifop-P-butyl over time as a function of plant height at the time of treatment. However, 14 days after treatment (DAT) all treatments displayed >89% injury. Bristly starbur response to fluazifop-P-butyl was similar to injury associated with contact-type herbicides.