Evaluation of Suitable Base Spray Rate Estimation Methods for Precision Chemical Applications in Vineyards with Different Training Systems

Background and goals Retrofit intelligent spray systems have been developed for precision agrochemical applications in perennial specialty crops. In such systems, although a 2-D, lidar-estimated, canopy density factor is used for individual nozzle actuation, the base spray rate (BSR; amount of spray liquid to treat unit canopy volume, L/m³) input critically governs the amount of spray mix delivered to the target. This rate is often decided by qualitative canopy characteristics and can be subjective. This study evaluated the suitability of three BSR estimation methods and resulting spray coverage, as well as deposition in modified vertical shoot position (MVSP)-trained winegrapes and high cordon (HC)-trained juice grapes.

Methods and key findings Canopy parameters at the full canopy growth stage were measured to estimate tree row volume (TRV), unit canopy row (UCR), and leaf wall area (LWA) attributes. These canopy attributes were used to estimate BSRs of 0.12, 0.30, and 0.14 L/m³ for MVSP-trained, and 0.13, 0.30, and 0.11 L/m³ for HC-trained grapevines, respectively. The grower-adapted application rate of 702 L/ha was used as a control.

Conclusions and significance Overall, the TRV-method estimated BSR and resulting spray applications had comparable spray coverage and deposition to control. Because TRV can be estimated with ease by the grower, it would ideally help to realize precision chemical applications in both MVSP- and HC-trained grapevines.