Dogfennel (Eupatorium capillifolium) Size at Application Affects Herbicide Efficacy

Abstract

Dogfennel is one of the most problematic weeds in Florida pasturelands and its control can become inconsistent as the plant matures. A premix of triclopyr + fluroxypyr has been recently introduced for weed control in pastures and rangeland; however, little published information exists concerning the control of dogfennel in pastures with this herbicide combination. Therefore, experiments were initiated to determine the efficacy of triclopyr + fluroxypyr compared with commonly used pasture herbicides on dogfennel at three heights. All herbicides utilized in this study are commonly used for dogfennel control. Dogfennel control was affected by both herbicide treatment and dogfennel height. In general, 0.80 + 0.28 kg ai/ha of 2,4-D amine + dicamba resulted in inconsistent control, especially as dogfennel plants increased in size. Increasing the rate of 2,4-D amine + dicamba to 1.21 + 0.42 kg/ha increased the consistency. Triclopyr + fluroxypyr provided similar levels of control as that of 1.21 + 0.42 kg/ha 2,4-D amine + dicamba. In all locations, control of 154-cm dogfennel was signficanatly lower than that of 38-cm dogfennel. These data indicate that triclopyr + fluroxypyr is an effective option for dogfennel control, but dogfennel height at the time of application is an important factor for optimizing control.