Abstract
Deposition of spray material containing a tracer dye was evaluated on leaf and fruit surfaces of citrus trees. Spray applications were made by a Bell UH1B Huey helicopter and a conventional PTO driven, trailered air carrier (air blast) ground sprayer in 1993; and in 1994 by a Bell UH1B Huey helicopter, and 3 ground sprayers, a PTO driven FMC 452 series air blast sprayer, a diesel engine driven FMC 937 CPD series air blast sprayer, and a Curtec Air Curtain sprayer. Spray volumes from helicopter and Curtec sprayers were 20% to 25% the volumes sprayed by the air blast sprayers. Water soluble dye, "Brilliant Blue" was washed from leaf and fruit surfaces (1993) or eluted from paper targets (1994) and the solutions analyzed for optical density in a spectrophotometer. The helicopter tended to deposit more spray material in the top canopy while the air blast sprayers favored the bottom and middle canopy and the Curtec sprayed uniformly over canopy heights. The dye tracer coupled with stick-on paper targets, provided a convenient means of assessing deposition to particular regions of the fruit or leaf surface. Surfaces of leaves and fruit oriented toward the sprayers tended to receive the preponderance of spray material, especially those closest to the spray outlet. Coverage was more uniform at greater distance from or out of the direct line of air source. It was concluded that greater turbulence was probably responsible for the more uniform spray coverage observed at increasing distance from the sprayers.
