Nonvertical Spray Angles Optimize Graminicide Efficacy

Abstract

Annual grasses constitute a major weed problem in winter annual crops in Northern Europe and especially in cropping systems where ploughing is omitted. At the optimum growth stage for control with POST herbicides, grasses have a predominantly vertical leaf orientation. This represents a very difficult spray target using the standard technique where nozzles are mounted more or less vertically downward. In this study, efficacy of the foliar-acting herbicide, haloxyfop, on perennial ryegrass at the two- to three-leaf stage was investigated in field experiments using some alternative configurations of nozzle mounting on the sprayer. Angling the spray either forward or backward relative to the direction of travel increased herbicide efficacy using standard commercially available flat-fan and pre-orifice nozzles. Efficacy increased generally with increasing angling relative to vertically downward and the forward-angled spray improved efficacy most. The largest improvement in efficacy was obtained using a 60° forward-angled spray in combination with a reduced boom height. Using this configuration, herbicide dose could be reduced by approximately 30% without loss of efficacy in comparison with the standard vertical mounting of nozzles. There was no advantage of using combinations of forward- and backward-angled nozzles.