Role of hedgerows in intercepting spray drift: Evaluation and modelling of the effects

When a pesticide is applied a proportion of the sprayed solution may become a cause of pollution in the surrounding environment, with ecotoxicological implications and phytotoxicity to other crops. In many countries buffer zones along field edges are recommended to shield surface waters, and hedgerows can play an important role in reducing pesticide risk. This study focuses on droplet drift, with the aim of evaluating the hedgerow efficacy in reducing drift from broadcast air-assisted sprayers and then to construct a simple model for estimating the spray drift level in surrounding fields. Three experiments were conducted in North-East Italy in 2004 and 2005, in winter, summer and autumn to obtain suitable optical porosity values in order to evaluate their effects. Three study situations (no hedgerow, single, double hedgerow) and two sprayer-hedgerow interaction scenarios (sprayer working perpendicular to or parallel with the hedgerow) were considered. Hedgerows were 7-8 m in height, while spray release height ranged from 1 to 2 m. The sampling method proved to be effective, with more than 73% of total amount sprayed being intercepted. Where there was at least one hedgerow, off-site spray reductions ranged from 82.6 (with optical porosity of 74.7%) to 97% (with optical porosity of 10.8%). The presence of a double hedgerow did not produce a higher interception rate. Analysis of the spatial pattern of drift showed that where there is a hedgerow with an optical porosity of 74-75%, the aerial drift caused by common broadcast air-assisted sprayers becomes negligible at a distance of 6-7 m. Hedgerows thus proved to be effective in intercepting spray drift leaving cultivated fields. In particular, low optical porosities provided high interception rates, even with very dense canopies, as no spray bypass was recorded. Spray drift profile was then modelled taking into account the effect of wind and optical porosity of a nearby hedgerow. A negative-exponential model is proposed. The model fits the experimental data quite satisfactorily and may be used to estimate spray drift magnitude in relation to wind speed and optical porosity of any hedgerow crossed by a droplets cloud spray drift.