R. C. Derksen

SPRAY CHARACTERISTICS AND DRIFT REDUCTION POTENTIAL WITH AIR INDUCTION AND CONVENTIONAL FLAT-FAN NOZZLES

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.

Effects of pressure differentials on the viability and infectivity of entomopathogenic nematodes

During passage through the different components of a spray application system, a nematode suspension will undergo pressure changes. The extent of damage to three species of entomopathogenic nematodes (EPNs) (Steinernema carpocapsae, Heterorhabditis bacteriophora, and Heterorhabditis megidis) in suspension due to the effects of a pressure differential was studied. A French pressure cell and press was used to subject the newly emerged EPN suspensions to a series of pressure differentials ranging from 1283 kPa (186 psi) to 10,690 kPa (1550 psi). Aged suspensions (3 weeks) of H. bacteriophora and H. megidis were also evaluated. Damage was quantified by counting living and dead (whole and pieces) EPNs and by bioassay techniques. As the pressure differential increased, the relative viability of the EPNs decreased. Entomopathogenic nematodes that survived the pressure differential were, in general, able to survive for at least 1 week and maintain infectivity to Galleria mellonella at rates equivalent to EPNs that had not been pressure treated. In general, the relative viabilities of fresh and aged EPNs were equivalent after pressure differential treatments. The relative viability of the treated EPNs remained above 85% for pressure differentials less than or equal to 1283 kPa for H. megidis and 2138 kPa (310 psi) for S. carpocapsae and H. bacteriophora, but decreased rapidly for higher pressure differentials. Greater reductions in relative viability were experienced by Heterorhabditis spp. than S. carpocapsae, indicating that nematode species is an important factor to consider when defining spray operating conditions. We recommend a maximum operating pressure of 1380 kPa (200 psi) for H. megidis and 2000 kPa (290 psi) for S. carpocapsae and H. bacteriophora.

DROPLET SPECTRA AND WIND TUNNEL EVALUATION OF VENTURI AND PRE-ORIFICE NOZZLES

Small- to medium-size droplets are desirable when applying insecticides and fungicides because they provide better penetration into the canopy and better coverage than larger sizes. However, small droplets can drift long distances. Several agricultural nozzle manufacturers have recently introduced so-called “low-drift” nozzles. Although manufacturers of low-drift nozzles claim these nozzles are considerably more effective in reducing spray drift than standard flat-fan nozzles, no independent data are available to support their claim. The objective of this study was to determine the effectiveness of two low-drift nozzles (TurboDrop® and Turbo TeeJet®) in reducing drift. The TurboDrop nozzle design incorporates a venturi air intake port and a pre-orifice chamber while the Turbo TeeJet nozzle design includes only a pre-orifice chamber. Nozzle evaluations were accomplished by measuring droplet sizes with a laser particle sizer and deposition distances of droplets in a wind tunnel (5 m/s). Data from measurements obtained with the low-drift nozzles were compared to data from a standard flat-fan nozzle. The low-drift nozzles produced fewer drift prone droplets and significantly lower downwind airborne deposits than the standard flat-fan nozzle (XR). In general, droplet size measurements taken along the long axis of the spray patterns showed less variation in volume median diameters for the XR and Turbo TeeJet (TT) nozzles than for the TurboDrop (TD) nozzles. The TD nozzles produced lower downwind deposits than TT nozzles operated at similar pressures (276 kPa); however, a larger orifice TT nozzle operated at a lower pressure (176 kPa) produced significantly lower downwind airborne deposits than the TD nozzle operated at 276 kPa. Covering or restricting the venturi air intake port on the TD nozzle increased nozzle output but had little impact on the overall droplet spectrum and downwind drift.

VISUAL AND IMAGE SYSTEM MEASUREMENT OF SPRAY DEPOSITS USING WATER–SENSITIVE PAPER

Water–sensitive papers (WSP) were attached to leaves in nursery trees and sprayed with air–blast sprayers. Deposit patterns on the WSP were rated visually for coverage, from 0 (no spots) to 10 (completely blue). Visual counts of spot density (spots/cm2) were made for cards representing coverage ratings from 1 to 6. WSPs were analyzed with an imaging system; several spot size parameters, number of spots, and area coverage percentage were measured. Visual ratings of 6, 7, and 8 had considerable variability in area coverage percentage. Sample WSPs with visual coverage ratings of 3, 5, 6, and 8 and minimum, median, and maximum coverage percentages are presented. Visually measured spot density was greater than image–system measured spot density for all rating numbers, especially for higher spot densities. Spot density began to decrease at visual rating numbers greater than 7.

Evaporation and Deposition Coverage Area of Droplets Containing Insecticides and Spray Additives on Hydrophilic, Hydrophobic, and Crabapple Leaf Surfaces

The efficiency of foliar spray applications is influenced by the evaporation and residual pattern of pesticide droplets on targets. Evaporation time and maximal coverage area of a single droplet from 246 to 886 m in size at relative humidity (RH) ranging from 30% to 90% were measured with sequential images under controlled conditions. Droplets were placed on targets inside an environmentally controlled chamber under a stereoscope and a high-definition digital camera. The spray mixtures used to form droplets included different combinations of water, a nonionic colloidal polymer drift retardant, an alkyl polyoxyethylene surfactant, and two commercially available insecticides. The droplet evaporation was investigated on crabapple leaf surfaces, and hydrophilic and hydrophobic glass slide surfaces. Adding surfactant into spray mixtures greatly increased droplet coverage area on the surfaces, while droplet evaporation time was greatly reduced. For a 343 m droplet on a crabapple leaf at 60% RH, the evaporation time decreased from 70 to 50 s and the maximal coverage area increased from 0.366 to 0.890 mm 2 after the surfactant was added into the spray mixture containing water and insecticide. Adding the drift retardant into the spray mixture slightly increased the droplet evaporation time and decreased the droplet coverage area. In addition, changing the target surface from the hydrophilic slide to the hydrophobic slide greatly increased the droplet coverage area and reduced the droplet evaporation time. Increasing RH increased the droplet evaporation time greatly but did not change the coverage area. The droplet evaporation time and coverage area increased exponentially as the droplet size increased. Therefore, droplet size, surface characteristics of the target (waxy or non-waxy), RH, and chemical composition of the spray mixture (water alone, pesticide, additives) should be included as important factors that can affect the efficacy and efficiency of pesticide applications.

Coverage and Drift Produced by Air Induction and Conventional Hydraulic Nozzles Used for Orchard Applications

A conventional, axial-flow, air-blast orchard sprayer was used to make applications to the outside row of a semi-dwarf apple block. Fluorescent tracer was applied at the same rate using either disc-core nozzle sets or air-induction nozzles fitted with flat-fan tips. The experiment included measuring the percent area of spray coverage on leaves after three variations in spray application method. Each of the variations used a different type of nozzle on the same conventional, axial-fan orchard sprayer. The three nozzle variations were a Spraying Systems D3-25 nozzle set, a Spraying Systems D4-25 nozzle set, and a TurboDrop 02 (TD02) air-induction nozzle set. Canopy spray deposits, downwind sedimentation, and airborne spray losses were also measured following treatment on the inside half of the outside row using D4-25 nozzles or TD02 nozzles. The small droplet spectrum D3-25 nozzle set produced the highest leaf surface coverage on both upperside and underside surfaces at 2.0 and 3.0 m heights in the canopy. The upperside leaf surface coverage produced by the D3-25 nozzle was only somewhat greater than the TD02 nozzle. It was, however, significantly higher than the D4-25 nozzle set at the 3.0 m height. Conversely, the underside leaf surface coverage produced by the D3-25 was significantly greater than the TD02 nozzle set at both 2.0 and 3.0 m heights and not statistically different from the D4-25 nozzle set at the lower sampling height. There were relatively few differences in canopy spray deposits between the D4-25 and TD02 nozzle sets. The TD02 treatment produced the lowest downwind sedimentation deposits on targets 8 to 32 m from the edge of the orchard. The D4-25 produced approximately three times higher deposits up to 9 m above the ground than the TD02 treatment on passive nylon screens located 8 m downwind from the edge of the orchard. The D4-25 treatment produced significantly higher airborne deposits on elevated, high-volume, air sampler filters out to 64 m. At 128 m, sedimentation and airborne deposits were similar for the D4-25 and TD02 treatments.

Evaluation of Spraying Equipment for Effective Application of Fungicides to Control Asian Soybean Rust

Summary Fungicides manufactured to control soybean rust are effective; however, successful control of this disease will mostly depend on proper application methods. Spray coverage and deposition from 10 application equipment/spray nozzles were analysed. In general, the spray treatments with air assistance were more effective in spraying rust fungicides than the treatments with the conventional boom sprayer. Spray performances from the boom sprayer with a canopy opener were very similar to the air assisted spray treatments, and were better than other treatments with the boom sprayer. Twin jet, Turbo Dual pattern and hollow cone nozzles produced lower spray performances than conventional flat fan nozzles. For treatments with the boom sprayer, medium spray quality provided higher spray coverage inside canopies than coarse and fine spray qualities. Future research will address how much fungicide inside canopies can be sufficient to control the soybean rust disease.

A History of Air-Blast Sprayer Development and Future Prospects

The design and operating procedures of air-blast sprayers have been greatly improved over the past 50 years. Early tree and vine spray application equipment used hand-guns that required a large amount of water. Later, sprayers with efficient fans, producing large volumes of air at high velocities, were developed for large fruit and nut trees. Recently, apple growers have planted many dwarf and semi-dwarf trees. In general, it is easier to produce more uniform coverage with less drift when spraying small trees than when spraying large trees. Modern designs such as tower, directed jet, and tunnel sprayers should reduce airborne spray drift and produce more uniform coverage. For optimum effectiveness, sprayer air-jet velocity, volume, and droplet spectra should be matched to the tree size, shape, and density. Besides optimizing delivery parameters, future sprayers will likely be required to handle biological materials with a greater variety of physical properties than the standard chemical materials used now. In addition, these materials will require spray systems that protect the live spray products from damage from heat, mechanical stress, and other factors that may kill the beneficial organism being applied.

DETERMINING THE INFLUENCE OF SPRAY QUALITY, NOZZLE TYPE, SPRAY VOLUME, AND AIR-ASSISTED APPLICATION STRATEGIES ON DEPOSITION OF PESTICIDES IN SOYBEAN CANOPY

Field studies were established in north central Ohio to determine the effect of different application strategies on targeting of foliar pesticides in narrow-row (18 cm) soybeans. Several different application factors were tested, including spray quality, nozzle type, air-assistance, and spray volume. In 2005, the spray mix included a fungicide. In 2006, in addition to the fungicide, an insecticide was included. Plant samples were removed from each test plot, and stems and leaves from the bottom third and middle third of the plant were separated for analysis. Overall, there was significantly less active ingredient found in the lower third of the canopies than the middle third, and significantly less pesticide residue was found on stems than leaves from the same canopy location. Significantly more fungicide residue was found on lower leaves treated by the medium-quality XR8004 flat-fan nozzle in 2005 than the coarse-quality XR8005 flat-fan nozzle. There were no differences in fungicide residue found on middle canopy leaves between the fine, medium, and coarse quality flat-fan nozzles. The twin-fan pattern nozzles (Turbo Duo and TwinJet) produced the lowest amounts of fungicide residue on the lower leaves in 2005. The mechanical canopy opener produced significantly higher fungicide residues on middle canopy leaves than all other treatments. The Jacto air-assist sprayer using JA3 hollow-cone nozzles produced the highest fungicide residues on lower canopy leaves in 2005. There were some statistical differences between the amounts of fungicide and insecticide residue found on plant tissue in 2006 because of the high amount of variability in the sample data. Overall in 2006, the higher volume XR8004 treatment (187 L ha -1 ) and the twin-fan TTJ60-11003 treatment at 145 L ha -1 performed similar to the Jacto sprayer making applications at 145 L ha -1 using either flat-fan or hollow-cone nozzles. In general, higher volume applications produced higher amounts of fungicide and insecticide residue on leaves from the middle of the canopy for conventional flat-fan and air-assist applications. Spray volume had less affect on residues measured on leaves from the lower canopy area. Across two years of different canopies at the same spray volume (145 L ha -1 ), the Jacto sprayer using JA3 hollow-cone nozzles produced more fungicide residue on middle canopy stems and lower canopy leaves than the medium-quality XR8004 flat-fan nozzle.

FOLIAR DEPOSITION AND OFF-TARGET LOSS WITH DIFFERENT SPRAY TECHNIQUES IN NURSERY APPLICATIONS

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.