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 runoffto surface water is possible and vegetated buffers are suggested as mitigationmeasure. Spinosad is an insecticide used to control pests in vineyards. Forregulatory purposes, FOCUS modelling is used to calculate pesticides runoffreduction provided by a vegetated buffer, but there is an urgent need forfield-based results. A field trial with artificial runoff was performed in September2017 in Northern Italy to evaluate the efficiency of a grassed buffer toreduce spinosad runoff. Trial conditions were based on FOCUS scenarios butmade worse to draw prudent conclusions. For the first time in Italy, the trialwas conducted according to Good Laboratory Practices to increase reliabilityof results and reproducibility of the study for regulatory purposes. Five plotswere 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 duringrunoff was 45 mm. Results show that the 12 m buffer completely retainedrunoff and effectively mitigated runoff concentration, and mean reduction ofspinosad concentration was 59%. A width effect exists, and every 6.5 m ofbuffer reduces concentration by 50%. Comparison of field results withFOCUS modelling shows that both VFSMod and LM models provide acceptableestimation of runoff reduction for a 5 m buffer, while LM seems moreprecise. For a 10 m buffer the VFSMod is very accurate, while LM underestimatesreduction observed in the field.