H. Erdal Ozkan

Droplet evaporation and spread on waxy and hairy leaves associated with type and concentration of adjuvants.

BACKGROUND Adjuvants can improve pesticide application efficiency and effectiveness. However, quantifications of the adjuvant-amended pesticide droplet actions on foliage, which could affect application efficiencies, are largely unknown. RESULTS Droplet evaporation rates and spread on waxy or hairy leaves varied greatly with the adjuvant types tested. On waxy leaves, the wetted areas of droplets containing crop oil concentrate (COC) were significantly smaller than those containing modified seed oil (MSO), non-ionic surfactant (NIS) or oil surfactant blend (OSB), whereas the evaporation rates of COC-amended droplets were significantly higher. On hairy leaves, COC-amended droplets remained on top of the hairs without wetting the epidermis. When the relative concentration was 1.50, the wetted area of droplets with NIS was 9.2 times lower than that with MSO and 6.1 times lower than that with OSB. The wetted area increased as the adjuvant concentration increased. MSO- or OSB-amended droplets spread extensively on the hairy leaf surface until they were completely dried. CONCLUSION These results demonstrated that the proper concentration of MSO, NIS or OSB in spray mixtures improved the homogeneity of spray coverage on both waxy and hairy leaf surfaces and could reduce pesticide use. This article is a US Government work and is in the public domain in the USA.

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.

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.

Spray deposition characteristics on tomatoes and disease management as influenced by droplet size, spray volume, and air-assistance

Few recommendations are available to help growers select application techniques to provide most efficacious control of vegetable diseases. Several different techniques, including low-drift, low- and high-pressure nozzles, and air-assisted delivery were evaluated over two years to assess differences in spray deposit characteristics and tomato disease control. Greater differences in coverage were observed between nozzles and machines than spray deposits. High-pressure sprays did not provide any better canopy penetration or coverage than low-pressure sprays. Air-assisted delivery was the only means found to produce significantly coverage on the undersides of leaves.

Spray Characteristics and Wind Tunnel Evaluation of Drift Reduction Potential with Air Induction and Conventional Flat Fan Nozzle

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 the laboratory conditions. Droplet sizes were measured with a laser imaging system, spray coverage on water sensitive papers (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 m/s). Tests were also conducted to evaluate the effect of air intake holes being closed 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, the air induction nozzles with two sealed air 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 pressure below the manufacturer’s recommended pressure range.

A Windows Version of DRIFTSIM for Estimating Drift Distances of Droplets

Computer simulation provides a means of determining the relative effects of various factors on spray drift while field experiments to measure spray drift have the limitation that many variables cannot be controlled. A Windows Version computer program (DRIFTSIM) was developed to rapidly estimate the mean drift distances of water droplets discharged from atomizers on field sprayers. This program interpolates values from a large data base of drift distances originally calculated for single droplets with a flow simulation program (FLUENT). The simulations of drift distances up to 200 m (656 ft) included temperatures (10-30 °C; 50-86°F), discharge heights (0-2.0 m; 0-6.56 ft), initial downward droplet velocities (0-50 m/s; 0-164 ft/s), relative humidity (10-100%), wind velocities (0-10.0 m/s; 0-32.8 ft/s), droplet sizes (10-2000 µm), droplet size distribution in Dv.1, Dv.5 and Dv.9, and 20% turbulence intensity. Variables can be either in metric or English units. For the input of droplet size distribution, drift distances are reported along with portion of volume in each class such as provided by many droplet size analyzers. The accuracy of the program FLUENT was verified with a uniform droplet generator and wind tunnel. The program indicates the relative effects of the input variables on drift distances and should, especially for large droplets, provide reasonable accuracy for many field applications.

Influence of spray additives on droplet evaporation and residual patterns on wax and wax-free surfaces

Evaporation time and wetted area of single droplets sizing from 246 to 886 µm at relative humidity (RH) ranging from 30 to 90% were measured with sequential images under controlled laboratory conditions. Droplets were placed inside an environmental-controlled chamber under a stereoscope and a high definition digital camera. The spray mixtures used to form droplets included different combinations of water, a polymer drift retardant, a surfactant, and two insecticides. The droplet evaporation was investigated on the surfaces of crabapple leaf surfaces, hydrophilic and hydrophobic glass slides, respectively. Adding surfactant into spray mixtures greatly increased droplet wetted area while droplet evaporation time was greatly reduced. For a 343 µm droplet on the crabapple leaf at 60% RH, the evaporation time decreased from 70 to 50 s and the wetted area increased from 0.366 to 0.890 mm2 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. Also, 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 could increase 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.

Development of a canopy opener to increase spray deposition and coverage inside soybean canopies

At the growth stage from R3 to R5, the foliage at the top of a soybean canopy takes the most part of the canopy and these top leaves cover the most area of the field. Because of the high foliage density at the top of canopy, conventional boom sprayers can hardly deliver sufficient chemical droplets to inner part of canopies. An experimental canopy opener was developed and attached on a conventional boom sprayer to increase spray deposition and coverage inside soybean canopies. The canopy opener consisted of a conduit pipe mounted on the spray boom upwind the nozzles. The conduit pipe opened the top part of canopies as the sprayer traveled to achieve better penetration of spray into lower parts of the soybean plant, where the rust infection first starts. Conventional flat fan nozzles were used for the test with the canopy opener for the application rate of 145 L/ha. Spray deposition and coverage at two heights inside canopies were determined. Treatments included three depths of the opener inside canopies, three horizontal distances of the opener from nozzles, and two nozzle sizes. A mathematical model was also developed to determine the plant deflection and traveling time so that droplets could be delivered inside canopies before the top part of canopy returning to vertical positions. Spray deposition and coverage inside canopies with the opener were also compared with a conventional boom sprayer without the opener. With the help of the canopy opener to push the top part of canopies, spray droplets had more space to reach middle and bottom of canopies, resulting in higher spray deposition and coverage on targets inside canopies.

Development of LIDAR-guided sprayer to synchronize spray outputs with canopy structures

Variable-rate application is an effective way for nursery and orchard growers to reduce pesticide use and potential contaminations to the environment. To realize this goal, an intelligent air-assisted sprayer implementing a high speed laser scanning sensor (LIDAR) was developed to vary spray output of each individual nozzle to match target tree needs in real time. Each nozzle was coupled with a pulse width modulation (PWM) solenoid valve to achieve variable rates based on the occurrence and canopy characteristics of the target, such as height, width and foliage density as determined by LIDAR. A unique density algorithm was developed to calculate foliage density by mapping the surface roughness of the canopy during the spray application. A back pressure control unit was integrated into the system to minimize the pressure fluctuation due to frequent changes in nozzle flow rates. Delay time between the sensor detection of the canopy and the nozzle activation was determined with a high-speed video camera. Laboratory tests demonstrated that the design criteria of the experimental sprayer were acceptable for performing variable rate functions.

An experimental variable-rate sprayer for nursery and orchard applications

Most chemical applications in orchards and ornamental nurseries are not target-oriented, resulting in significant loss of pesticides and contamination of the environment. To avoid over- and under-application of chemicals, sprayers must be designed to apply the appropriate amount of pesticide based on the tree canopy characteristics such as tree height, width, volume, and foliage density. A precision air-assisted sprayer with variable flow rate of individual nozzles was tested for treating ornamental nursery and fruit trees. The sprayer was developed using a modified conventional air-assisted orchard sprayer by implementing a laser scanner to detect canopy characteristics, five-port air-assisted nozzles coupled with pulse width modulation (PWM) solenoid valves to deliver spray, and an automatic flow rate controller to minimize pressure fluctuation. Sprayer treatments included the new precision sprayer, the same precision sprayer without the intelligent control activated and a conventional, axial flow, air blast sprayer in an apple orchard at three different growing stages. Measurements were made for spray deposition and coverage inside canopies, losses on the ground and beyond target trees, and airborne drift downwind from the target trees. Compared to conventional sprayers, the variable-rate sprayer produced relatively uniform spray coverage and deposition inside canopies, and reduced spray volume by 47% to 73% with significantly less off-target losses on the ground, through gaps between trees, and in the air.