Effectiveness of grassed buffer in reducing spinosad runoff: real data and FOCUS output

In Italy high-quality vines are grown on sloping fields where pesticide runoff to surface water is possible and vegetated buffers are suggested as mitigation measure. Spinosad is an insecticide used to control pests in vineyards. For regulatory purposes, FOCUS modelling is used to calculate pesticides runoff reduction provided by a vegetated buffer, but there is an urgent need for field-based results. A field trial with artificial runoff was performed in September 2017 in Northern Italy to evaluate the efficiency of a grassed buffer to reduce spinosad runoff. Trial conditions were based on FOCUS scenarios but made worse to draw prudent conclusions. For the first time in Italy, the trial was conducted according to Good Laboratory Practices to increase reliability of results and reproducibility of the study for regulatory purposes. Five plots were tested, each simulating a grassed buffer of 12 m length on a slope of 10% - 13%. The artificial runoff was 200 mm in 3 hours and rainfall pre- and during runoff was 45 mm. Results show that the 12 m buffer completely retained runoff and effectively mitigated runoff concentration, and mean reduction of spinosad concentration was 59%. A width effect exists, and every 6.5 m of buffer reduces concentration by 50%. Comparison of field results with FOCUS modelling shows that both VFSMod and LM models provide acceptable estimation of runoff reduction for a 5 m buffer, while LM seems more precise. For a 10 m buffer the VFSMod is very accurate, while LM underestimates reduction observed in the field.