Volume, Speed, and Distribution Technique Effects on Poinsettia Foliar Deposits

The influence of spray volume, application speed, and distribution technique on spray deposits found on greenhouse poinsettias was investigated. Foliar spray deposits were measured on upperside and underside leaf surfaces in the top and bottom canopy locations. Five different application techniques were used to treat 12-week-old, bench-grown, greenhouse poinsettias. High-volume, high-pressure techniques were used to simulate variations on conventional application practices. Air-assisted, electrostatically charged sprays were used to simulate low volume, hand-directed, application techniques. A mechanical aerosol generator was used to simulate low volume applications generated at a single point and intended to fill the greenhouse with a fog. Spray deposition was measured by spectral analysis of food dye tracer. Spray deposits were higher in the top canopy location and on the upperside leaf surfaces. The lowest spray deposits were found in the bottom canopy location and on the undersides of those leaves. Hand-directed distribution techniques resulted in significantly higher spray deposits compared to the whole-room fogging spray distribution technique. Slower applications that doubled the total application time and that were made using the same spray volume as higher speed applications nearly doubled underside leaf deposits. The greatest variability in spray deposits was found with higher application speeds and reduced volume applications made through the high pressure handgun. It was observed that the higher spray volumes increased spray deposits through redistribution resulting from run-off and touching leaf surfaces.