Model to Predict Spray Deposition in Citrus Airblast Sprayer Applications: Part 2. Spray Deposition

Abstract

A model was developed to simulate spray dispersion and predict pesticide deposition in citrus trees when using an air-carrier sprayer. The model can be split into two parts: (1) dispersion, which focuses on spray transport and droplet dispersion in open space, and (2) deposition, which focuses on spray transport and deposition inside a canopy. The dispersion part of the model and its validation were presented in the first part of this article. This second part presents details of the deposition component of the model and validation with data from a field experiment. The experiment involved spray application of a fluorescent dye solution to orange trees using a conventional airblast sprayer, and sampling leaves at two heights and four canopy depths. The spray treatments, consisting of combinations of two nozzles (Albuz ATR Lilac and Blue) and two forward speeds (2.4 and 4.8 km h-1), were applied in a randomized complete block design with five replications. Samples were analyzed by fluorometry, and leaf area was measured with an area meter. The results showed good agreements between the model output and the experimental data for canopy deposition, with the best predictions yielding a modeling efficiency and correlation coefficient of 61.3% and 0.92, respectively. However, the ground deposition data were overly underpredicted by more than three orders of magnitude and were not considered appropriate. This shortcoming notwithstanding, the model has potential for meeting the set objectives, and it has been implemented in an expert system to assist spray applicators in making decisions critical for efficient spray operations.