Influence of application volume on the efficacy of clodinafop-propargyl and fenoxaprop-P-ethyl on oats

Abstract

The influence of application volume on the efficacy of clodinafop-propargyl and fenoxaprop-P-ethyl on cultivated oats (Avena sativa) was studied in the glasshouse. Both herbicides were more efficacious when applied in 75 L ha -1 than in 300 L ha-1, with 11002 and 11006 nozzles respectively. However, when the same two volume rates were created by varying the speed of a 11003 nozzle, clodinafop-propargyl efficacy was not affected by application volume, whereas fenoxaprop-P-ethyl remained more efficacious at 75 L ha-1. This suggests that in the first experiment, fenoxaprop-P-ethyl efficacy was affected by changes in both spray quality and concentration, whereas only the former influenced clodinafop-propargyl efficacy. The hypothesis that the fenoxaprop-P-ethyl formulation was more influenced by concentration than clodinafop-propargyl was supported by dynamic surface tension studies and measures of active ingredient retention by oat plants. Within the practically relevant concentration range considered, surface activity of clodinafop-propargyl remained low, with little influence on herbicide retention. In contrast, depending on the concentration, surface activity of fenoxaprop-P-ethyl was below or above levels that were critical for its retention. Although these differences may not be as apparent in the field as in the glasshouse, our study certainly indicates that both clodinafop-propargyl and fenoxaprop-P-ethyl are herbicides favoured by low application volumes. © 2008 The Authors.