Effects of Pneumatic Atomization Spraying on Pesticide Deposition Efficiency and Control Efficacy Against Postharvest Gray Mold in Cut Roses

To address the problems of pesticide waste, cross-infection, and low efficiency associated with traditional postharvest gray mold control in cut roses, this study aims to explore and establish an efficient and low-pesticide-consumption chemical control technique.

The droplet size and density of pesticide were determined using the water-sensitive paper method to optimize the operational parameters for pneumatic atomization spraying. Three main cut rose cultivars, ‘Peach Avalanche’ ‘Nightingale’ and ‘Jumilia’, were used as test materials to systematically compare four pesticide application methods. The treatments included: (1) pneumatic atomization spraying at 0.40 MPa, (2) hydraulic electric spraying at 0.25 MPa, (3) hydraulic manual spraying at 0.16 MPa, and (4) traditional flower head dipping. Their effects on pesticide deposition parameters and gray mold control efficacy were evaluated. Pesticide deposition parameters were determined using the allura red tracer method and the water-sensitive paper method. Two-level multiple linear regression models of deposition and control efficacy were constructed to quantitatively analyze the relationships among application parameters, deposition efficiency and control efficacy, and to explore the internal mechanism underlying the differences in control efficacy among different treatments.

(1) Spray pressure and target distance significantly affected droplet characteristics during pneumatic atomization spraying. The volume median diameter (VMD) was the smallest and droplet density the highest at 0.4 MPa and 40 cm target distance, representing the optimal application parameter combination. (2) The droplet volume diameter produced by pneumatic atomization spraying was 87.7 μm, the droplet density was 332.6 droplets/cm², and the uniformity (CV=8.85%) was significantly better than that of hydraulic electric spraying and hydraulic manual spraying. (3) The pesticide deposition rate of pneumatic atomization spraying reached 67.6%, which was equivalent to 89.0% of that of flower head dipping (76.0%). This value was significantly higher than that obtained with hydraulic electric spraying (33.7%) and hydraulic manual spraying (24.7%). (4) After 96 h of simulated postharvest cold-chain transportation, the gray mold incidence of ‘Peach Avalanche’ treated with pneumatic atomization spraying was only 5.56%, with a control efficacy of 82.18%, which did not differ significantly from that of traditional flower head dipping, but was significantly superior to that of conventional hydraulic spraying methods. Notably, the pesticide dosage per stem was merely 0.27 mL, representing an 84.66% reduction compared with that of flower head dipping (1.76 mL/stem). On the 8th day of vase life, the survival rate of cut flowers treated with pneumatic atomization spraying ranged from 60% to 70%, comparable to that of traditional flower head dipping. Two-level multiple linear regression models were constructed for droplet parameters-deposition efficiency (adjusted R²=0.964) and deposition efficiency-control efficacy (adjusted R²=0.838). The results confirmed that pneumatic atomization spraying, with its high droplet density and superior deposition performance, achieved optimal control efficacy. (5) Verification tests on ‘Nightingale’ and ‘Jumilia’ confirmed that pneumatic atomization spraying achieved stable control efficacy across cultivars with differing resistance levels, exhibiting no significant difference from traditional flower head dipping.

Pneumatic atomization spraying is a postharvest gray mold control technology with the advantages of high efficiency, pesticide use reduction and cost savings, which can provide important support for improving the quality and efficiency of the cut rose industry.