Effect of operational parameters of UAV sprayer on spray deposition pattern in target and off-target zones during outer field weed control application

•Deposition of droplet increased with decrease in flight altitude and speed.•Droplet density and coverage decrease with the increase of flight speed and altitude.•D0.5 increased with the decrease in flight spread and altitude.•More than 90% deposition accrues in the target zone using single rotor UAV sprayers. Droplet size, weather conditions and operational parameters of sprayers also affect the spray coverage, absorption attachment to the target. Unmanned aerial vehicles (UAVs) currently, is considered a modern spraying technology which is helpful for efficient spraying. However, the effect of operational parameters on deposition in target and off-target zones still required to determine. Field tests were conducted to determine spray deposition, the number of spray deposits, coverage and droplet size under various flight heights (2 and 3 m) and flight speed (2 and 3 m/s) for control of outer field control. DepositScan software was applied to determine the spray deposition, number of deposits, coverage and droplet diameter. The results showed that the average deposition (2.29 µL/cm2) in the target area was found the highest when the UAV operates with 2 m/s forward speed at 2 m height (T1), the spray coverage under the T1 treatment achieved 36.19% at zero position of the central flight line. At the flight central line, the relative span was 0.70, 1.01, 1.03 and 1.05 for treatments T1, T2, T3 and T4 respectively. The treatment T1 showed maximum VMD = D0.5 as 448.75 µm whereas T4 showed minimum D0.5 with a value of 238.95 µm. The deposition in the off-target zone was nearly negligible for single-rotor UAV. This study provides a recommendation UAV operators, farmers and manufacturers for better utilization of this modern technology for weed control.