Optimization of spray application on bed-grown vegetables. On-going developments within OPTIMA project.

The development of a smart sprayer for carrot is one of the issues of the OPTIMA IPM project (www.optima-h2020.eu). The general design of this sprayer is combining several smart components with optimized application technologies adapted to crops grown in beds like carrot. A Decision Support System (DSS) uses local weather forecasts (resolution of about 1 km²) combined with an epidemiological model for Alternaria in order to predict potential infection periods. Alternaria disease is identified by using an Early Detection System (EDS) where disease spots are identified in images from a multispectral camera and dynamic detection is possible with deep learning. Besides the development and implementation of these smart components, the sprayer itself is also optimized. A first series of experiments was aimed at selecting the most appropriate nozzles and nozzle arrangements. Clusters of four nozzles are defined to spray on a single crop bed. Within a cluster, the distance between nozzles equals the boom height in order to focus sprays on crop beds in a way that distances/heights are adapted to crop development stage. Assuming the broadcast application is deemed to provide an acceptable biological efficacy, a potential dosage reduction of up to 60% can be reached when nozzle distance/height is 0.4 m corresponding to early development stage (Zwertvaegher et al., 2020).
Additional functionalities of the OPTIMA sprayer for carrots are studied in the project. A variable air support mounted on the boom sprayer is specifically designed using an electrical driven fan able to adapt the airflow in order to increase spray deposition and penetration inside the canopy, but also to reduce spray drift. Preliminary investigation with a 2 m wide prototype boom including four nozzles was tested showing contrasted results depending on the spray configuration at early and late development stages of carrots. Field tests will be conducted in 2021 to cross compare the reference situation using FF110 04 nozzles – 12 km h-1 – 158 L ha -1 without any smart devices with the smart sprayer including the optimized set of low drift nozzles and the air support. Deposition and spray drift will be tested according to ISO 25522 and ISO 22866 protocols respectively. PWM nozzle control is implemented on the sprayer in order to allow variable rate applications (VRA) according to a prescription map based on the EDS and DSS. This VRA functionality will be operated in the fields with either synthetic fungicides or BioPPP selected for their efficacy against Alternaria in laboratory conditions. Results of these field investigations will be presented.