Study on spray droplet drift and deposition characteristics under different nozzles and environmental conditions for knapsack and boom sprayers

Spray drift during pesticide application remains a critical environmental concern, particularly under natural wind conditions. This study presents a field evaluation of drift behavior of knapsack and boom sprayers based on 15 standardized field trials conducted in accordance with ISO 22866:2005. Experiments were performed under three wind speed categories: low (0–3.3 m s−1), moderate (3.4–5.4 m s−1), and high (≥5.5 m s−1). Drift deposition, droplet density, and spray coverage were evaluated using two hollow-cone nozzles on knapsack sprayers (Li Cheng KZ 80–06 and KZ 80–20) and two flat-fan nozzles on boom sprayers (Li Cheng VP110015 and VP11005). Results showed that boom sprayers were more susceptible to wind effects, with drift increasing significantly under moderate and high wind conditions. The boom sprayer with the VP11005 nozzle generated the highest near-field drift, reaching 108% at 1 m distance. Conversely, the knapsack sprayer with the coarser KZ 80–20 nozzle produced minimal drift, recording only 36.9% at 1 m under moderate winds. A strong positive correlation (R2 = 0.94) was observed between spray coverage and drift deposition. The findings recommend restricting Li Cheng VP11005 nozzle operation to low-wind conditions only, providing practical guidance for drift mitigation and for optimizing pesticide application strategies.