Accuracy assessment of Drone and Knapsack sprayers for droplet characters, herbicide efficacy, weed control efficiency and crop productivity in transplanted rice

Weed infestation is a major constraint in transplanted rice, causing significant yield losses when not effectively managed. Conventional weed control methods, such as manual weeding and knapsack sprayer application, are labour intensive, inconsistent, and often inefficient. Drone-mounted spraying has recently emerged as a precision weed-management tool, offering improved spray coverage, uniformity, and reduced chemical use. A field experiment was conducted during the rainy ( Kharif ) seasons of 2023 and 2024 at Gangavati in the semi-arid tropics of India to compare the efficacy of a drone-mounted sprayer with that of a conventional battery-operated knapsack sprayer. The study evaluated spray characteristics, weed dynamics, crop yield, and economic returns under the sequential application of pre-emergence (PE) pendimethalin followed by post-emergence (PoE) Bispyribac sodium. The drone-mounted sprayer achieved a significantly (p = 0.05) wider swath width (3.42–3.58 m), higher discharge rate (1764–1766 ml min⁻¹), and superior spray uniformity (∼99.12%) than the knapsack sprayer (swath width 2.28–2.52 m; uniformity ∼89%), resulting in improved spray coverage and droplet deposition. Sequential application of pendimethalin 37.5 CS at 2.3 ml l⁻¹ followed by bispyribac sodium at 0.5 ml l⁻¹ through the drone significantly reduced weed density (5.84 m⁻²) and weed biomass (4.38 g m⁻²) and increased weed control efficiency (65.05%), which was comparable to farmers’ practice (77.85%). Moreover, drone-based spraying resulted in higher crop productivity and economic returns than knapsack spraying. Overall, drone-mounted spraying ensured precise droplet placement, better canopy penetration, and enhanced herbicide efficiency while reducing labor requirements, saving time, and minimizing operator exposure to chemicals. Thus, drone-assisted herbicide application represents a sustainable and efficient alternative to conventional knapsack spraying for weed management in transplanted rice.