Spray drift deposition on off-field zones next to field crops using Drift Reducing Technologies in the Netherlands

The Dutch government’s policy (Environmental Activities Decree, Sustainable Crop Protection 2) has set goals for the reduction of the emission of plant protection products into the environment. Data are needed on actual spray drift and drift reducing measures when spraying a plant protection product to support decision making on the authorisation of the use of plant protection products in different crop types (Board for the Authorisation of Plant Protection Products and Biocides, Ctgb). The WUR Drift Calculator (WDC) is introduced in 2021 for use in the authorisation procedure of plant protection products (Ctgb) from January 2022 onwards. The WDC is based on updated spray drift data from spray drift measurements in the period 1995-2005. This means ongoing and new procedures up till that date of introduction may still use the spray drift values as used in the authorisation procedure and based on spray drift measurements in the period 1995-1999. This report provides tables of spray drift deposition from boom spray applications on the different evaluation zones until the WDC is in place in the authorisation procedures. Results are presented in a matrix of Drift Reducing Technology (DRT) versus crop-free buffer zone for applications in a bare ground situation and a crop situation. Data were extrapolated from performed spray drift experiments; in order to assess spray drift deposits for the distance at which the off-field threshold level to protect non-target terrestrial arthropods (NTA), non-target terrestrial plants (NTP) and surface water (SW) is likely to be met when spraying a plant protection product onto a crop, or onto a bare soil/short crop situation. When using boom sprayers in field crops, in the authorisation procedure the standard spray drift deposition on the off-field evaluation zone was 10% of the applied dose for non-target arthropods (NTA), 4.7% for non- target plants (NTP) and 1.0% for surface water (SW) until the end of 2017. Since the 1st of January 2018 the Environmental Activities Decree prescribes the compulsory use of at least DRT75 (75% drift reducing techniques) to be used on the whole field. This means spray drift deposition on the off-field evaluation zone changed to 5.5% for non-target arthropods (NTA), 0.9% for non-target plants (NTP) and 0.5% for surface water (SW). These values are based on a conventional boom sprayer application with standard non drift- reducing flat fan nozzles (until end of 2017) and a DRT75 from January 2018 and a spray boom height of 50 cm above the crop canopy. For arable crops, spray drift deposition is evaluated at a 1.0 m wide zone at 0.5-1.5 m for NTA and at 1.5-2.5 m distance for NTP relative to the centre of the last crop row and for SW at 1.5-2.5 m from the field edge or top of the bank of the surface water body. For NTA/NTP the last crop row is defined at 1.0 m from the edge of the field, whereas for SW it is at 1.50 m from the top of the bank for intensively sprayed crops and at 0.50 m for other crops. Spray drift was investigated for a standard application technique and various drift-reducing techniques, for both a mature crop (height >20 cm) and a situation with bare soil of short crop (height <20 cm). Drift-reducing techniques (DRT) are classified in different classes, representing drift reduction levels of 50%, 75%, 90%, 95%, 97.5% and 99% compared to the standard application technique. This classification system is based on deposits at the SW evaluation zone. However, the drift-reducing effect depends strongly on the distance of the evaluation zone from the crop; usually for NTA, NTP and SW evaluation zones a certain application technique gives rise to different drift reductions. Still, drift reducing techniques are relevant for NTA/NTP risk assessments as well. Representative techniques for each of the DRT classes are chosen and spray drift deposition is calculated on the NTA, NTP and SW evaluation zones for applications using boom sprayers in the crop and the bare soil/short crop situation. At this moment the DRTs 75 up to 99 are used in the NTA/NTP evaluation procedure whereas for SW this is the DRTs 75 to 95. Also, the effect on spray drift deposition at the evaluation zones is assessed for additional buffer zone widths up to 4 m.