Performance Evaluation of a Newly Developed Variable-Rate Sprayer for Nursery Liner Applications

An experimental variable-rate sprayer designed for liner applications was tested by comparing its spray deposit, coverage, and droplet density inside canopies of six nursery liner varieties with constant-rate applications. Spray samplers, including water-sensitive papers (WSP) and nylon screens, were mounted inside tree canopies to collect spray deposit and coverage from variable-rate and constant-rate (555 and 1,110 L ha-1) applications. Models for estimating spray volume savings of the variable-rate sprayer compared to constant-rate and tree-row-volume (TRV) rate applications were developed for various liner canopy sizes and tree spacings. The accuracy of the model was validated with the field test data. For the liner trees tested, the variable-rate sprayer delivered 151 to 359 L ha-1 application rates, while the conventional constant-rate application required 1,110 L ha-1. Due to substantially lower spray output, the variable-rate application had lower (but sufficient) spray deposit, coverage, and droplet density than the constant-rate applications. The variable-rate application also had significantly less variations in spray deposit within canopies of different-size trees. Test results showed that the variable-rate sprayer reduced spray volume by up to 86.4% and 70.8% compared to the 1,110 L ha-1 and TRV-based rate applications, respectively, while the model-estimated savings were up to 94.6% for the 1,110 L ha-1 application and 57.7% for the TRV-based rate applications. Therefore, the newly developed variable-rate sprayer would bring great reductions in pesticide use and safeguard the environment for nursery liner production.