Variability of wind conditions in citrus groves compared with those recorded outside

Wind velocity and direction, which are normally reported at certain time intervals, fluctuate substantially within a short time frame.  These fluctuations may have a significant effect on spray deposition of air-assisted sprayers used in citrus production.  Wind measurements are usually made inside or outside a grove at about 10 m height but the latter may not accurately represent the wind conditions within the grove.  The objective of this study was to compare data recorded by the Florida Automated Weather Network (FAWN) outside the grove at 10.0 m above the ground with the measurements made within a citrus grove at different heights.  Within the grove, wind velocity and direction data were collected at 10.0, 3.6, 3.0, 2.4, 1.8, 1.2, and 0.6 m above the ground at 1-s interval.  For the same period, FAWN data were available at a minimum of 15-min interval.  Results of the 10-m height measurements showed good correlation between wind conditions recorded outside grove and those collected within the grove (r = 0.69 and 0.94 for wind velocity and direction, respectively).  However, average wind velocity and direction at both sites were significantly different (p = 0.05).  Within the grove, wind velocities of 1.5 m/s or less, recorded at 10 m height, showed almost zero wind velocity at lower heights.  Within the grove, maximum wind velocities recorded at 3.6 – 0.6 m amounted to only 59% – 20% of wind velocity recorded at 10 m, respectively.  Averaging wind velocity over 15-min interval reduced the wind variability of 1‑s interval by 90%.  For field characteristics similar to those described in this study, wind conditions recorded at 10 m height outside grove cannot reliably represent wind conditions inside grove, particularly within the canopy height.   Keywords: FAWN, spraying conditions, wind direction, wind measurement site, wind sensor, wind velocit

Assessment of spray distribution with water-sensitive paper

The purpose of this article is to highlight the limitations of water-sensitive paper in characterizing spray droplet distribution and deposition in field application.  Spatial distributions of spray droplets discharged from an airblast sprayer were sampled on pairs of absorbent paper (AP) and water-sensitive paper (WSP) targets at several distances from the sprayer.  Spray solutions, containing a fluorescent tracer, were discharged from two nozzle sizes to achieve low and high volume rates commonly used in citrus applications.  Spray deposits on AP targets were measured by fluorometry and spray coverage areas on WSP cards were assessed by three independent image analysis systems.  Generally, there were good correlations (R2 = 0.9085 to 0.9748) among the three imaging systems in measuring WSP percent area coverage.  Lower volume rate (smaller droplets) provided more useful WSP targets than higher volume rate (larger droplets).  Overall, there were somewhat weak correlations between WSP area coverage and AP spray deposition measurements.  Volume median diameter and number of droplet stains on WSP cards, obtained by only two imaging systems, showed noticeable differences between the measurements of the two systems.    Keywords: WSP, image analysis, spray volume rate, spray coverage, spray droplet siz

Effects of sprayer operating parameters on airborne drift from citrus air-carrier sprayers

Florida citrus is mostly sprayed with various types of air-carrier sprayers.  These sprayers differ substantially in design features and are normally operated at different volume rates and ground speeds, during day and night applications.  The main objective of this study was to characterize drift potential (not total drift) of several commonly used citrus sprayers when operated under typical application conditions (different operating variables).  Drift potential of the applications was assessed by capturing samples of airborne spray droplets with two high-volume air samplers, positioned above tree canopies at two sides of the spray course.  For most applications, higher spray volumes (larger droplets) showed significantly reduced drift potential than lower volumes.  Higher ground speed appeared to have more drift potential compared to lower speed but the effect of speed was not significant.  Nozzles with comparatively lower flow rates (smaller droplets) were generally more drift-prone than the ones with higher flow rates (larger droplets) and spray from the upper nozzle bank had higher drift potential than spray from lower nozzles.  These results are comparative and could show the importance of optimizing spray variables to reduce drift from typical citrus applications.Keywords: spray drift, spray volume rate, sprayer ground speed, air sampler, fluorometry   

A Method for Assessing Drift Potential of a Citrus Herbicide Applicator

The main objective of this study was to evaluate the suitability of the DEIAFA drift test bench system (Dipartimento di Economia e Ingegneria Agraria, Forestale e Ambientale; University of Torino, Italy) for assessing drift potential of a citrus (Citrus sp.) herbicide applicator. The study involved testing the effects of spray drift shield, nozzle type, and ground speed on drift potential of the applications. It was carried out in randomized block design within a split-split-plot experiment with five replications. A computational analysis procedure for evaluation of deposit values, measured along the test bench, was developed to compare the treatments in terms of a drift potential index (DPI). The methodology provided repeatable results. Among the treatments, ground speed was the main factor affecting the DPI. Both nozzle types tested [flat fan extended range nozzle (XR) and wide-angle deflector nozzle (TT)] showed higher DPI at faster speed. Decreasing the ground speed from 6.0 to 3.0 km·h−1 decreased the drift potential on average ≈35%. The performance of XR nozzle was improved by the presence of spray drift shield (27% reduction in DPI). However, the shield did not affect the drift potential of the TT nozzle significantly. The results were significantly affected by the wind velocity normalized by its direction relative to the sprayer travel; therefore, the tests should be carried out in relatively calm wind conditions, as much as possible

Assessment of aerosol deposition and movement in open field conditions

Overall objective of this study was to evaluate the dispersion of aerosol plumes generated by a truck-mounted ultra low-volume (ULV) applicator and a hand-held thermal fogger under open field conditions.  Experiments were also planned to determine the relative capture efficiencies of various sampling techniques in such applications.  The ULV applicator was used at three travel speeds (8.5, 16.8, 24.8 km/h) and the thermal fogger at two release heights (0.6 and 1.1 m above ground) to investigate the effect of speed or release height on deposition at 6, 12, 24, and 48 m downwind.  High volume air sampler (HVS), low volume air samplers (LVS), spinning cotton ribbon (CR) samplers, polypropylene green plastic cards (GC), acetate cards (AC), and water-sensitive papers (WSP) were used to collect deposits.  The ULV applicator was tested with water and oil sprays while the thermal fogger was tested with the latter tracer only.  Using water- and oil-based tracers, all deposition targets were analyzed by fluorometry.  Results showed decreased tracer deposition with increase in sampling distance.  Overall, travel speed affected deposition at the near sample locations only, but in most sample locations, normalized deposits were comparable at all speeds.  Spray release height did not affect deposition of active samplers but had significant effect on deposition of passive samplers at 6 m location only.  Overall, the higher release height resulted in more deposition in most downwind locations.  There were good correlations between depositions on active and passive samplers. The HVS, CR, GC, and AC samplers were effective in sampling aerosol plume dispersion under open field conditions.  The paper includes relationships among capture efficiencies of various samplers.Keywords: ULV applicator, thermal fogger, deposition samplers, Yellow 131SC dye, Pyranine 10G, fluorometr