J. van de Zande

Modelling spray drift from boom sprayers

A random-walk model, IDEFICS, is described to compute downwind spray drift from conventional boom sprayers in chemical crop protection. Spray deposits are computed downwind from the sprayed crop field. The model basically is two-dimensional (2D), but close to the spray nozzle the model is 3D, incorporating driving speed and entrained air-currents below the nozzle. Input parameters are related to the geometry of the field, to the boom sprayer settings and to environmental factors. The model was calibrated with a set of field trials using an experimental single-nozzle sprayer in a cross wind. In the trials, tap water containing a fluorescent dye was used as the spraying liquid, and downwind deposits were measured by fluorimetry. Variations of boom height, spray nozzle size, driving speed and liquid pressure were examined, at varying wind speeds. Both experiments and simulations showed that boom height, wind speed and nozzle size were the major factors affecting spray drift. Surprisingly, liquid pressure did not affect downwind spray deposits at all. A comparison between model results and results of a practical field trial showed a good agreement if field trials were averaged over several replications. The variation between individual replications is however too large to use single trials for model verification. Further calibration trials are needed to investigate the effect on drift of multi-nozzle arrangements, crop height and medium- and coarse-sized spray nozzles.

Precision Disease Control in Bed-Grown Crops

Matching spray volume to crop canopy sizes and shapes can reduce the use of plant protection products , thus reducing operational costs and environmental pollution. Developments on crop adapted spraying for fungal control are highlighted in arable crop spraying. A plant-specific variable volume precision sprayer, guided by foliage shape and volume (canopy density sprayer ; CDS ) was developed for bed-grown crops to apply fungicides . Sensor selection to quantify crop canopy and spray techniques to apply variable dose rates are evaluated based on laboratory measurements. Based on the laboratory experience a prototype CDS sprayer was built using either a Weed-IT ® or a GreenSeeker ® sensor to detect plant place (fluorescence) or size (reflectance). Variable rate application was either done with a pulse width modulation nozzle or a switchable four-nozzle body. Spray volume could be changed from 50 to 550 l ha−1 in 16 steps. Spray deposition , biological efficacy and agrochemical use reduction were evaluated in a flower bulb and a potato crop during field measurements using a prototype CDS sprayer. Spray volume savings of a prototype plant-specific sprayer are shown to be more than 75% in early late blight ( Phytophthora infestans ) control spraying in potatoes . In flower bulbs (lily ) it was shown that in Botrytis blight control on average spray volume could be reduced by 45%. In a potato crop biological efficacy was maintained at the same good level as of a conventional spraying. In a flower bulb crop biological efficacy of the CDS was lower than of conventional spraying, which means that spray strategy and dose algorithms need further research.