Spray Deposition and Mass Balance in Citrus Orchard Applications

A sampling system was used to quantify on-canopy spray deposition and off-target losses from five air-carrier sprayers commonly used in citrus spray applications. The samplers consisted of continuous loops of cotton ribbon that were stretched out above the tree canopies, on the tree sides, and above the orchard floor. The loops extended to the third rows on each side of the spray course. The sprayers had different design configurations, and their airflow rates, nozzle selections, droplet size spectra, and operating parameters varied markedly. Spray solutions containing a fluorescent tracer were applied between two tree rows, the targets were collected in small segments, and spray deposition on various sample sections was quantified by fluorometry. The study was conducted in five replications. Overall, there was no significant difference in canopy deposition of the sprayers, and spray deposition on tree rows adjacent to the sprayer accounted for 73.0 - 79.4% of the total sprayer output. Cumulative deposition of three rows on both sides of the sprayers ranged from 74.3 to 82.1%, and the off-target losses (ground deposit plus spray drift) amounted to 17.9 - 25.7%. Comparing ground deposits or drift estimates alone, there were significant differences among the five sprayers. Ground deposits ranged from 8.7 to 19.6%, and drift estimates were mostly in the 6.1 - 14.0% range.