Assessment of Three Commercial Over-the-Row Sprayer Technologies in Eastern Washington Vineyards

Materials and Methods

General experimental design. For all sprayers (Figure 1), canopy deposition, aerial drift, and ground drift were evaluated at two timings: early-season (BBCH 55 or 65), and midseason (BBCH 75, 77, or 79; Lorenz et al. 1994). Specific canopy and drift assessment methods are described below in the “Spray deposition and drift collection and processing” section. Sprayer evaluation comparisons were made only within a single sprayer type. Thus, no comparisons are made among sprayer types.

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Figure 1

Over-the-row commercial sprayers evaluated in this study in Washington state in 2016 and 2017. (A) VineTech Quantum Mist; (B) Blueline Gregoire SpeedFlow; and (C) On Target Spray Systems electrostatic.

A summary of sprayer operation information, including dates of sprays, vine growth stage, and sprayer-specific operating metrics, is presented (Tables 1 and 2). At each of the two sites (described below), evaluations for vine development stage were repeated both spatially and temporally. At site 1, two different vineyard blocks (2.5 ha each) were used for sprayer evaluation: a south quadrant and a north quadrant. In 2016, only the north quadrant was used on each sprayer evaluation date, and in 2017, both quadrants were used. In 2016 at site 1, the early-season evaluation timing was conducted on day of the year (DOY) 144 and in 2017, it was conducted on DOY 136 and 142. In 2016, midseason evaluation timing at site 1 was conducted on DOY 174 and 210 and in 2017, it was conducted on DOY 206 and 227. At site 1, between the two years and two different vineyard quadrants, each sprayer and timing combination was evaluated three different times. At site 2 (6.6 ha), sprayer evaluation was conducted in 2017 only. The early-season evaluation timing was conducted on DOY 157 and the midseason evaluation timing was conducted on DOY 208. On each day, two different locations in the vineyard block at site 2 were used for evaluation, so the sprayer and timing combination was evaluated two times.

Site and equipment descriptions. Site 1 description. Site 1 was a commercial vineyard in the Horse Heaven Hills AVA (45°59´N; 119°38´W) in Paterson, WA. The vineyard was established in a Warden very fine sandy loam soil (coarse-silty, mixed, superactive, mesic Xeric Haplocambids) and Hezel loamy fine sand soil (sandy over loamy, mixed, superactive, nonacid, mesic Xeric Torriorthents [USDA-NRCS 2019]). The vineyard was planted in 1980 in a north-south row orientation to own-rooted Vitis vinifera Chardonnay on a 1.8 m × 3.1 m vine by row spacing. The vine canopy was trained to a modified vertical shoot-positioned (VSP) system with a single, centered catch wire allowing both east and west sides of the canopy to flop out and downward. Vine-row-volume measurements were taken within a 3 m area in a non-data row. Canopy width and height (edge to edge of the canopy growth and from the top of the cordon to the top of the canopy growth, respectively) were calculated from five measurements of each type (Tables 3 and 4). Vineyard irrigation and pest management programs followed grower standard practices for the site.

Site 1 sprayers. Two commercial sprayers were examined in this vineyard. Both the Quantum Mist and Gregoire sprayers were fitted with a rate controller, TeeJet 844-AB and Arag Bravo 180s, respectively, during sprayer evaluations for both seasons.

The first sprayer was a Croplands Quantum Mist, distributed by VineTech (65 horsepower requirement), a three-row, over-the-row sprayer operated by a John Deere 5100M tractor (100 horsepower). The sprayer had 12 axial fan heads, equally divided on six hydraulic arms: that is, two fan heads per arm (Figure 1A). Each fan head had six locations for nozzles and used hydraulic, grey hollow cone Teejet VisiFlo TX-VK8 nozzles. In 2016, due to rapid early-season growth at the time of application, six nozzles were used for all application dates at a spray volume rate of 702 L/ha. In 2017, the early-season applications occurred when canopy sizes were smaller, so only four nozzles arranged in a square pattern were used at a spray volume rate of 468 L/ha. In the late-season applications, six nozzles were used with a spray volume rate of 702 L/ha (Table 2). Sprayer calibration and optimization were done with direct on-site assistance of manufacturer representatives, according to their regional specifications. Fan heads were set facing forward, toward the front of the sprayer, at an ~45° angle into the canopy, not facing directly toward the opposing fan head (Figure 1A). Air velocity was recorded ~0.5 m from the nozzle to represent the distance from the sprayer to the canopy at the canopy closest to the sprayer on the opposed row (24 km/hr) and the unopposed row (17 km/hr).

The second sprayer was a Gregoire Speedflow Progress, distributed by Blueline Manufacturing (50 to 80 horsepower requirement), a three-row, over-the-row sprayer operated by a John Deere 5520 tractor (89 horsepower; Figure 1B). Sprayers were donated for use from the manufacturer and a different machine of the same model was donated in each year. The sprayer was equipped with a FLEXIspray system, consisting of six flexible PVC-coated polyester fabric tubes on hydraulic arms with five nozzles per arm. To accommodate the height of the canopy and nozzle selection while preventing the tubes from touching the ground, a simple modification of switching inlet tubes was made so that the bottom three nozzles operated in a group and the top two operated as a group. Original tubing had the top three nozzles clustered independently from the bottom two. In both seasons, only the bottom three nozzles were used in the early-season applications at a spray volume rate of 234 L/ha and all five nozzles were used in late-season applications at a spray volume rate of 468 L/ha (Table 2). This pneumatic sprayer was equipped with a Gregoire air-shear, DynaDiff diffuser nozzle. The sprayer calibration and optimization were done with direct on-site assistance of manufacturer representatives, according to their regional specifications. The fabric tubes were set facing backwards, away from the front of the sprayer, at an ~20 to 30° angle into the canopy, not facing directly toward the opposing fabric tubes and nozzles (Figure 1B). Air velocity was recorded ~0.5 m from the nozzle to represent the distance from the sprayer to the closest canopy on the opposed row (26 km/hr) and the unopposed row (23 km/hr). Though individual sprayers and rate controllers differed between years, the application rate, engine speed, and operating pressure were all maintained at a consistent rate.

Site 2 description. Evaluations were also conducted in 2017 on a commercial vineyard located in the Columbia Valley AVA (46°32´N; 119°49´W) in Mattawa, WA. The vineyard has Ritzville silt loam soil (coarse-silty, mixed, superactive, mesic Calcidic Haploxerolls) (USDA-NRCS 2019). The vineyard was planted in 2011 in a north-south row orientation to own-rooted V. vinifera Riesling on a 1.5 m × 2.4 m vine by row spacing. The canopy was trained to a strict VSP and the vineyard’s irrigation and pest management programs followed grower standard practices for the site. Vine-row-volume measurements were also taken at site 2, as previously described.

Site 2 sprayer. The On Target sprayer, manufactured by On Target Spray Systems Inc. (20 to 32 horsepower requirement), is a two-row, over-the-row electrostatic sprayer (Figure 1C). This sprayer was operated by a Kubota M8540 tractor (86 horsepower). The sprayer was equipped with eight PVC tubes, each with five electrostatic pneumatic nozzles. All nozzles were used the entire season for both applications at a rate of 198.3 L/ha (Table 2). Prior to field tests, the nozzles were checked with a voltmeter (ASIMT33D-CA, AstroAI) to ensure 1000 V electricity was present at each nozzle as is required for electrostatic charge of the droplets. This sprayer did not use a rate controller and was calibrated and optimized with direct onsite assistance of manufacturer representatives, according to their regional specifications. PVC tubes, and thus nozzles, were oriented at 90° to the vine row, directly opposite the opposing tube and nozzles (Figure 1C). Air velocity was not recorded for this sprayer.

Travel speed calculations. For all sprayers, tractor speed was calculated before each spray trial application. The tractor was operated at the same settings during a tracer application with the power take-off (PTO) engaged and at the rotations per minute (rpm) of the intended application with a full sprayer tank. The specified gear and tractor rpm for each application was recorded (Table 2) and adjusted to account for changes during the growing season, including spray volume delivered and canopy size. The tractor speed was timed over a set-length course (91.44 m) and calculated as kilometers per hour (km/hr).

Weather and canopy measurements. Environmental parameters, including wind speed (km/hr), wind direction (°), relative humidity (RH, %), and air temperature (°C), were collected continuously during spray applications. During spray applications, either a handheld Kestrel Instruments 3000 anemometer or an all-in-one weather station (ATMOS 41; ME-TER Group Inc.) connected to a data logger (CR1000; Campbell Scientific) was used to acquire environmental data at 0.02 Hz (Tables 3 to 5). The weather station was mounted ~3 m aboveground. On days that the all-in-one ATMOS 41 weather station did not record weather data, the corresponding wind direction data was pulled from Washington State University’s AgWeatherNet (weather.wsu.edu) weather station network, since the handheld anemometer does not collect that type of data. At site 1, the AgWeatherNet Paterson West station was used at the first midseason evaluation (DOY 174) in 2016 and at both midseason applications (DOY 206, 227) in 2017. This station is located within 5.6 km of the site and has an elevation difference of 3 m. For site 2, the AgWeatherNet McClure station was used at midseason (DOY 208) in 2017. This station is located within 19.6 km of the site and has an elevation difference of 312 m. Collected environmental parameters conformed to ISO standards (±25% deviation for wind speed, ±10% deviation for RH, and ±5% deviation for temperature between the tests being compared) on all days except Gregoire midseason in 2017 (ISO 2007). On those particular days (DOY 206 and 227), the deviation during spray application was 23% in temperature, 26% in RH, and 49% in wind speed.

Spray deposition and drift collection and processing. A 500 mg/L solution of fluorescent tracer (Keystone Pyranine 10G; Milliken) dissolved in water was applied during field trials. Tank samples were collected pre- and post-application to determine tracer concentration and to normalize data across spray dates. Canopy deposition, aerial drift, and ground drift were determined by collecting spray deposition on 5 × 5 cm plastic cards (card placement described below). This method of using plastic cards is appropriate at low to moderate volume spray applications and for in-field (short distance) drift studies (Forster et al. 2014, Rathnayake et al. 2021). Cards were made from Stark Boards Disposable Cutting Boards.

Canopy spray deposition – Experimental design. To collect spray deposition within the canopy, collection poles facilitated placement of plastic cards throughout different zones of interest. Poles were constructed from schedule 40 2-cm PVC pipe and metal alligator clips (5.1 cm × 1.1 cm; Figure 2A and 2B) to attach the plastic collection cards. At site 1, 15 canopy poles were placed in two rows (opposed spray row and unopposed spray row) to accommodate the three-row sprayers (Figure 2E). Site 2 had 15 canopy poles in a single row, since it was a two-row sprayer (Figure 2F). Collection zones in the canopy included west upper canopy (WUPP), middle upper canopy (MidUPP; site 1 only), east upper canopy (EUPP), west fruiting zone (WFZ), and east fruiting zone (EFZ) (ISO 22522:2007 2007). Distance between plastic cards in the upper canopy and fruiting zone was ~17 cm at both sites. The larger canopy at site 1 necessitated an additional card in the MidUPP, positioned halfway between EUPP and WUPP and raised 3 cm (Figure 2A). Site 2 had a more tightly trained canopy, so MidUPP was excluded (Figure 2B). The unopposed row was sprayed on one side in the first pass, and the other side in a second pass. Thus, both sides of the canopy received spray deposition, but with unopposed air applications.

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Figure 2

Field collectors and vineyard collection locations for sprayer evaluations in Washington State in 2016 and 2017. (A) Canopy deposition collection pole with five collection zones for Quantum Mist and Gregoire sprayers at Site 1; (B) Canopy deposition collection pole with four collection zones for On Target sprayer at Site 2; (C) aerial drift collection poles; and (D) ground drift collection block. Field trial configuration for (E) Site 1 and (F) Site 2 for 2016 and 2017 trials, showing in-canopy (opposed and unopposed rows), aerial drift, and ground drift collection points in the vineyard during data collection after tracer applications. Graphic art by Dr. Charlotte Oliver, Washington State University.

Aerial and ground drift – Experimental design. Aerial drift poles with similar construction as those used for collecting canopy deposition (Figure 2C) were placed in the first three rows downwind from the sprayed row (Figure 2E and 2F). Aerial drift was collected at 0.3, 0.6, and 0.9 m above the canopy. To collect ground drift, wooden blocks (10 × 17 cm) were placed in the middle of the interrow (equal distance from either neighboring vine row), downwind of the spray application row and upwind of aerial poles (Figure 2D). Plastic cards were affixed under a rubber band.

Deposition and drift collection procedures. Post application, tracer solution was allowed to dry for ~10 min on the plastic cards before collection, and each card was placed into an individual bag (Uline). General best practice protocols (such as changing gloves and discarding compromised cards) were followed to prevent contamination between samples. All samples (tank and cards) were immediately placed in a dark, thermally insulated cooler with ice packs to avoid tracer degradation during transport back to the lab, where they were stored at 1.6°C within 5 hrs of field collection. At this temperature, samples can be stored up to 90 days with minimal deterioration (Nairn and Forster 2015). All samples were analyzed within 60 days of collection.

Deposition quantification. An aliquot of deionized water was added to each individual collection bag or tank sample, then shaken for 1 min at 180 oscillations/min (Model: 6010, Eberbach shaker). A sample of this solution was poured into borosilicate glass cuvettes and analyzed using a fluorometer (10-AU, Turner Design). The concentration reading (parts per billion; μg/L) was recorded for each sample. All samples with concentrations exceeding the upper limit of the fluorometer (1000 μg/L) were diluted to read again in the linear range of developed calibration curves. Each sample reading was corrected using a calibration curve produced from tracer standards made from each chemical lot of tracer specific to a trial (Khot et al. 2012).

Powdery mildew disease ratings. Cluster disease ratings of grapevine powdery mildew, Erysiphe necator, were conducted for each sprayer in both years. Disease ratings were estimated visually as percent surface area infected. Ratings were collected in-field on 30 clusters per treatment replicate typically collected between 25 Aug and 1 Sept each year; typically immediately preharvest. The level of disease present at all sites and both years were considered acceptable by the associated commercial entity. In 2016 at Site 1, clusters in the Quantum Mist trial had an average incidence and severity of powdery mildew of 1% and 0.3%, respectively. In 2016 at Site 1, clusters sprayed by the Gregoire had an average incidence and severity of powdery mildew of 3% and 0.3%, respectively. In 2017 at Site 1, clusters in the Quantum Mist trial had an average incidence and severity of powdery mildew of 80% and 16%, respectively. In 2017 at Site 1, clusters sprayed by the Gregoire had an average incidence and severity of powdery mildew of 62% and 15%, respectively. In 2017 at Site 2, clusters sprayed by the On Target had an average incidence and severity of powdery mildew of 70% and 10%, respectively.

All partnering growers used systemic fungicides as a part of their routine fungicide program. Systematic products are generally absorbed by the plant, which can overcome disease management limitations related to deposition patterns of the applied product (Wise et al. 2010). Because of this, we could not compare how spray deposition from each sprayer may have influenced powdery mildew disease control in those sprayed blocks.

Statistical analyses. Fluorometry readings were normalized for tank sample concentrations across all sprayers and application days to allow comparison within a sprayer type. No comparisons were made among sprayer types or across dates. Deposition differences between and within canopy zones and drift was analyzed with an analysis of variance and least standard squares, followed by post-hoc comparison of means using Tukey’s honest significant difference (JMP; ver. 14.0.0, SAS Institute, Inc.). Significant differences (α = 0.05) were examined by sprayers across application growth timings and between spray dates, position of spray card target within the vineyard, and overall amount of deposition from each sprayer.