Spray drift potential, spray coverage, droplet size, and spray pattern width for various sizes of air induction and conventional flat-fan nozzles with equivalent orifice areas were investigated and compared under laboratory conditions. Droplet sizes were measured with a laser imaging system; spray coverage on water-sensitive paper (WSP) was evaluated with a boom sprayer at a constant travel speed in a greenhouse, and ground and airborne spray deposits were determined in a wind tunnel at two wind velocities (2.5 and 5.0 m/s). Tests were also conducted to evaluate the effect of air-intake holes being sealed or open on spray characteristics of air induction nozzles. With the equivalent nominal flow rate, air induction nozzles had approximately 2.1 to 2.75 times larger exit orifice areas than the conventional nozzles. With the equivalent orifice area and equal liquid flow rate, there was no significant difference in droplet size, spray pattern width, spray coverage, ground spray deposit, and airborne deposit among regular air induction nozzles, air induction nozzles with two sealed air-intake holes, and conventional flat-fan nozzles. Spray characteristics of air induction nozzles could be achieved by conventional nozzles with the equivalent orifice size operated at the reduced operating pressure.

Information is lacking on spray techniques to improve deposit uniformity within nursery canopies and reduce off-target loss on the ground and via spray drift from the treated area. Spray deposits at various elevations within crabapple trees and on the ground were investigated with an air blast sprayer equipped with conventional hollow-cone nozzles, air-induction nozzles, and conventional hollow-cone nozzles with a drift retardant in a commercial nursery field. Airborne deposits at three elevations on sampling towers and on the ground at several distances from the sprayer were also investigated with the three spray treatments in an open area without trees. To compare field test results, wind tunnel experiments were conducted to assess spray deposits on the floor beyond 0.4 m downwind distance from the nozzles and airborne deposits at 2.1 m downwind from the spray discharge point with the three spray techniques without air assist. Droplet size distributions across spray patterns without air assist were measured with a laser particle/droplet image analysis system. In general, there was no significant difference for deposits within nursery tree canopies and on the ground with three different spray techniques. At the 700 L/ha application rate, which was 360 L/ha lower than the rate typically used in nursery application, the tree canopies received over 4 to 14.5 times as much spray deposit as actually needed from all treatments, and a large portion of spray volume deposited on the ground. Compared with conventional hollow-cone nozzles, drift reduction from air-induction nozzles or the spray mixture with drift retardant treatment was significant in wind tunnel tests but was not significant in field tests.

Spray coverage specifications for commercially available nozzles could help applicators determine the optimal nozzles for effective control of insects, diseases, and weeds. Spray coverage and deposit density from seven types of nozzles at three different flow rates (0.76, 1.14, and 2.27 L min −1) and two target positions (0.50 and 0.70 m below the nozzle) were evaluated with water-sensitive papers (WSP) as targets under controlled environmental conditions. These nozzles included 80 • and 110 • conventional flat-fan nozzles, air induction flat-fan nozzles with the air intake hole either opened or sealed, hollow-cone nozzles, turbo jet nozzles, and twin-jet fan pattern nozzles. Spray coverage (percent area of a WSP covered with spray depositions) increased as flow rate increased for all nozzles. The hollow-cone nozzles had the highest coverage at both target positions while air induction nozzles had the lowest coverage. With the same flow rate, the 80 • nozzles had higher spray coverage than 110 • nozzles. Nozzles producing coarse spray had the lower spray coverage than nozzles producing fine and medium sprays. The 80 • and 110 • flat-fan nozzles at lower-than-specified operating pressures produced spray as coarse as that from the air induction nozzles with similar coverage. There was no significant difference in spray coverage between the same air induction nozzles whether the two air intake holes were opened or sealed. Spray coverage on targets at the 0.50 m position was greater than that at the 0.70 m position. Therefore, careful selection of nozzles could provide comparable performance for economical and effective spray coverage with optimal flow rates and operating pressures.

No abstract

No abstract