Spray atomization and deposition patterns of one newtonian and two pseudoplastic formulations after aerial application over a mature conifer forest in Newfoundland

Abstract

Spray atomization and deposition patterns of three formulations were investigated in five aerial spray trials in Newfoundland, to understand the inter‐relationships between physical properties, drop size spectra and recovery of the spray volume at ground level. Diflubenzuron (DFB) was sprayed at 30 g active ingredient in 2.0 L/ha. Futura XLV (Fu‐XLV) and Thuricide® 48LV (Thu‐48LV), spray formulations of Bacillus thuringiensis (B.t.), were both applied undiluted at 30 BIU/ha, but in volume rates of 2.1 L/ha and 2.36 L/ha respectively. Each of the three formulations was applied over a 15 ha plot using a Piper Pawnee aircraft fitted with six Micronair® AU5000 atomizers. Spray drops were sampled with Kromekote® cards and deposits were collected on glass plates. Physical properties measured were: viscosity at variable shear rates, volatility and surface tension. The viscosities increased progressively from low (for DFB), moderate (for Thu‐48LV) to high (for Fu‐XLV) values, showing a gradual increase in pseudoplastic behaviour of the three formulations. The volatility data indicated an inverse relationship to the viscosities, but the surface tensions were similar for all the formulations.

The highly pseudoplastic Fu‐XLV atomized into the least wide drop size spectrum. The Newtonian formulation of DFB, on the other hand, atomized into the widest drop spectrum; and the moderately pseudoplastic Thu‐48LV, into an intermediate drop spectrum. Thus viscosity and volatility were more important factors in liquid atomization and drop deposition, than surface tension. Among the three meteorological factors measured, relative humidity appeared more important in drop deposition than did wind speed and temperature, within the range measured.     

Assessment of aerial spray deposits in a spruce forest using in‐flight microencapsulation technique

Abstract

Spray drops were counted and sized on Kromekote® cards at ground level, and on spruce foliage at canopy level, after aerial application of a formulation containing a microencapsulation medium, over a spruce forest in Ontario. The majority of drops (70%) on foliage was 20 ‐ 75 µm range. A coarse drop size spectrum was observed on cards with a maximum diameter (Dmax) of 380 µm, and with 85% of the drops = 130 µm in diameter. Foliar drop analysis, on the other hand, indicated a finer spectrum with a Dmax of 150 µm, and with 85% of the drops = 75 µm. These results were explained on the basis of formulation ingredients, atomizer setting, weather factors, and drop retention on target surfaces. The assessment of spray deposits on glass plates at ground level indicated that about 16% of the applied spray volume reached the forest floor, a value which is comparable to those obtained in previous forestry applications using the ultra‐low‐volume (ULV) technique.     

Phosmet residues in an orchard and adjacent recreational area 1

Abstract

Two cover sprays of phosmet were applied to an orchard adjoining a camping area and a bird sanctuary with a resident goose population. Insecticide residues were monitored on orchard leaves, orchard ground cover, ground cover in the camp‐site and along the adjacent lakeshore. Despite attempts to minimize drift, significant spray residues were found outside the target area. Residues on ground cover and leaves were reduced by sprinkler irrigation subsequent to spray application.     

Influence of surfactant concentration on foliar retention of pesticides used in forestry

Abstract

Aqueous tank mixes of permethrin, fenitrothion, Bacillus thuringiensis (B.t.), diflubenzuron (DFB), and glyphosate containing different amounts of Triton® X‐114, a nonionic surfactant, were prepared. Glyphosate formed clear solutions, permethrin and fenitrothion formed emulsions, DFB and B.t provided suspensions. Emulsion stability of permethrin and fenitrothion increased with increasing surfactant level, while the emulsion drop size decreased.

Foliage of white oak, trembling aspen, white spruce and balsam fir were dipped in tank mixes of pesticides (except B.t.) labelled with ¹⁴carbon. The amount of pesticide retained on foliage was determined by liquid scintillation counting. Foliage was also dipped in non‐radioactive B.t. tank mixes, and the protein retained was determined colorimetrically. With all tank mixes, a direct relationship was observed between the mass of liquids retained on foliage and liquid viscosity. In contrast, the amount of pesticide retained was unaffected by viscosity, but was influenced by emulsion drop size. Initially, the amount of pesticide retained on foliage increased with increasing surfactant concentration. Beyond an optimum surfactant level, the emulsion drop sizes were too small and the emulsions became too stable to allow maximum retention of pesticides on foliage. With the glyphosate solutions, however, no optimum surfactant level was indicated because foliar concentrations continued to increase with increasing surfactant levels.     

Dose transfer of Bacillus thuringiensis from cabbage to the diamondback moth: A graphical simulator

Abstract

The application of agrichemicals is a highly inefficient process and one of the main causes of the environmental and health risks currently associated with pesticide usage. Efforts to mitigate this inefficiency have largely been unsuccessful, due principally to the poor understanding of the processes involved in the spray application of pesticides, from atomization to biological effect. A generalized model of the application system for pesticides from atomization to biological result is described in this overview. The model allows the investigation of the biological consequences of altering the application parameters for the bacterial insecticide Bacillus thuringiensis when used against the diamondback moth (Plutella xylostella L.) with cabbage as the substrate. Parameters input into the model include the in‐flight droplet size frequency distribution of the spray cloud, spatial distribution of the deposit, spread and subsequent environmental degradation of the deposit, and behavioral and toxicological effects.

It is hoped that such a modelling approach can afford insights into the application process, and, through a better understanding of the inefficient but still highly effective hydraulic application systems used worldwide, reduce that inefficiency to tolerable levels.     

Polymer and invert emulsifying oil effects upon droplet size spectra of sprays

Abstract

A series of wind tunnel atomization studies were carried out to investigate the effects of polymer and invert suspension oil “drift control adjuvants” upon the droplet size distribution spectra produced by nozzles typically used in aerial and ground based spraying of pesticides. A D8–46 disc and core was used as a typical aerial application nozzle, and an 8003 fan nozzle was used for the ground based sprayers simulation. The droplet size spectra were evaluated in a wind tunnel using a Malvern 2600 laser particle size analyzer immediately upon mixing and at 15 minutes after re‐circulation through a pumping system. The addition of the polymer‐based adjuvants significantly increased the droplet size spectra parameters of the spray cloud, but all the polymer products showed signs of breakdown of their molecular arrangements in the liquid medium, as a result of agitation. The invert suspension oil adjuvant did not change the droplet size spectra markedly, nor did it show signs of breakdown of the internal liquid structure after re‐circulation.     

Effect of in vitro administered 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on DNA-binding activities of nuclear transcription factors in NIH-3T3 mouse fibroblasts

Abstract

Most modern pesticides are expensive. Application of excessive dosage rates is likely to cause undesirable biological side‐effects and is economically wasteful. Non‐uniform distribution of the spray cloud, or application at the wrong time, may result in failure to control the pest. It is the responsibility of the field operator to acquire sufficient knowledge and skill to ensure proper use of the control agents, to increase efficiency of their usage and to reduce unwanted side‐effects. To achieve this goal, he must take into consideration the various physical factors that govern field performance of pesticides.

A simple relationship exists between the spray volume and emission rate used, and droplet size produced. The use of extremely low spray volumes (i.e., those less than 2.0 litre per ha) for forest insect control in Canada, as opposed to higher volumes used in agriculture, necessitates the release of fine droplets (ranging from 20 to 70 μm in diameter) to obtain adequate coverage of the target area. These droplets take a long time to sediment downwards, evaporate in‐flight, become smaller in size and/or form powdery residues, thus contributing to off‐target drift and impaired droplet adhesion to target surfaces. Physical factors such as rain washing, degradation by sunlight and erosion by wind also influence the longevity of pesticide deposits on foliage which is crucial during the critical period of pest control.

Factors affecting the mode of entry into insects are related to the type of ingredients used in formulation. If a pesticide acts via crawling contact, formulations which would provide surface deposits would be more beneficial than emulsions or oil‐based mixes which tend to undergo penetration into foliar cuticle. Physical factors that affect field performance of a pesticide tank mix are related to phase separation and ‘breakdown of emulsions’ in the application equipment; ‘agglomeration and caking’ of wettable powder dispersions at the bottom of the tank; impaired flow behaviour of highly viscous formulations; and coarse atomization of high‐viscosity tank mixes leading to poor target cover.     

A preliminary examination of the translocation of microencapsulated cyfluthrin following applications to the perimeter of residential dwellings

Abstract

Methods have been developed to monitor the translocation of microencapsulated cyfluthrin following perimeter applications to residential dwellings. A pilot study was implemented to determine both the potential for application spray to drift away from dwellings and the intrusion of residues into homes following perimeter treatments. Residential monitoring included measuring spray drift using cellulose filter paper and the collection of soil samples from within the spray zone. In addition, interior air was monitored using fiberglass filter paper as a sorbent medium and cotton ball swabs were used to collect surface wipes.

Fortification of matrixes resulted in recoveries of >90%. Spray drift was highest at the point of application and declined to low but measurable levels 9.1m from the foundations of dwellings. Soil residues declined to low, but measurable levels by 45 days post‐application. No cyfluthrin was measured from indoor air; however, some interior surfaces had detectable levels of cyfluthrin until three days post‐application.

Findings indicate that spray drift resulting from perimeter applications might contaminate non‐target surfaces outside the spray zone. Soil borne residues may serve as persistent sources for human exposure and potentially intrude into dwellings through the activities of occupants and pets. Residues do not appreciably translocate through air and consequently inhalation is not a likely route for human exposure. Surface residues detected indoors suggest that the physical movement of residues from the exterior to the interior might be a viable route of movement of residues following this type of application.     

Spray Charging and Trapping Scrubber for Fugitive Particle Emission Control

The control of fugitive process emissions (FPE) with Spray Charging and Trapping (SCAT) scrubber was evaluated both theoretically and experimentally. The SCAT uses air curtain and/or jets to contain, convey, and divert the FPE into a charged spray scrubber.

Experiments were performed on an 8000 cfm bench-scale spray scrubber to verify the theory and feasibility of collecting fugitive particles with charged water spray. The effects of charge levels on drops and particles, nozzle type, drop size, gas velocity, and liquid/gas ratio on collection efficiency were determined experimentally. The results of the experiments and the comparison between theory and data are presented.

An air curtain was developed for conveying the FPE to the spray scrubber, deflecting the crosswind, and containing hot buoyant plume. The design and air flow field for the air curtain are presented.     

Minimizing drift and exposure from knapsack sprayers

Abstract

An improved drift shield for attaching to the lance of conventional knapsack sprayer to reduce wind induced drift and operator exposure was designed and tested. The drift shield consists of a conical wire frame covered with polythene and has an annular opening at the point of attachment to the lance which allows air to be drawn into the shield while spraying. Tests conducted with winds in the range of 1.25–5.75 m/s show that wind can increase the width of spray swath from an unshielded lance, up to 4.3 times the normal swath in no‐wind condition. Use of a conventional shield contained the swath width within 3.5 times and the improved shield restricted the swath width to 3.1 times the normal swath. Spray deposit from an unshielded lance, within the normal swath decreased to as low as 45%, due to wind effects. However, use of the conventional, and the improved shields enhanced the spray deposit to 54.2% and 68%, respectively. The improved drift shield improved the spray pattern displacement (SPD) significantly (P<0.05) compared with the conventional shield and the unshielded lance when the wind speed exceeded 1.25 m/s. The improved shield decreased the off target drift by as much as 63% compared with the unshielded spray. It also decreased the quantity of pesticide deposit on the operator's body by 41–84% and thereby reduced exposure and improved safety.     

Determination of pendimethalin (PROWL®480 EC) spray drift from ground applications

Abstract

Pendimethalin herbicide (PROWL^®480 EC) spray drift was determined from ground applications representing the highest rate applied to corn in eastern Canada. A novel drift collector pattern was laid out on the ground immediately before herbicide application. Most of the drift collectors were located downwind of the application target area. The maximum labelled rate of 1.68 kg ai/Ha was applied on 2 occasions on separate sites. In both applications, drift collector cards indicated that concentrations of pendimethalin were not detectable outside the target zone (<0.01 μg/cm²) at or beyond the 10 metre drift collector stations. Risk assessment calculations indicated that non‐target organisms would not be at significant risk from off‐site movement of pendimethalin.     

In situ assay with the midge Kiefferulus calligaster for contamination evaluation in aquatic agro-systems in central Thailand

The aims of this study were to verify the suitability of in situ tests using the tropical midge Kiefferulus calligaster and to evaluate the most sensitive endpoint for the assessment of aquatic pesticide contamination. In situ tests were carried out in freshwater drainage channels (farm channels) that supply vegetable crops and receive considerable pesticide spray drift, and at channels outside farms (main channels). Moreover a pesticide-free farm was used as reference site. The endpoints analysed were: survival of the larvae, body length increment, capsule width increment, cholinesterase activity and glutathione S-transferase activity. Seasonal change was investigated as rainy season and dry season. Deleterious effects were observed at some farms especially during the rainy season when farmers apply heavier doses of pesticides. However, high mortality rates observed in main channels suggest that these water bodies are also affected by other impacts besides pesticide use. This work shows the potential of the in situ assay with K. calligaster as a tool for the environmental quality assessment of tropical aquatic ecosystems.     

Comparison of the droplet size spectra produced by rotary atomizers and hydraulic nozzles under simulated aerial application conditions

Abstract

A wind tunnel was used to characterize the droplet size spectra of liquid sprays from several different atomizers and nozzles used under simulated aerial application conditions. The atomizers included a D8–46 nozzle, a Through Valve Boom (TVB) nozzle, and rotary cage and drum atomizers.

The D8–46 hydraulic nozzle was evaluated, using water, at orientations of 0, 10, 20, 30, 40, 50, 60, 70, 80 and 90° relative to 145 and 180 km/h airstreams. The TVB nozzle was evaluated using water, water with isopropyl alcohol, and water with a non‐ionic surfactant at airstream velocities between 130 and 180 km/h. The rotary atomizers were evaluated at different rotation rates, flow rates of water and an insecticide, in 130 and 180 km/h airstreams.

The volumetric droplet size spectra parameters (D_vo.x) decreased as the angle of the D8–46 nozzle and the airstream velocity increased. Empirical models were developed to predict these values for different windspeed and nozzle angle conditions. The TVB nozzle produced larger droplets than the other atomizers under similar conditions, with a decrease in the D_vo.x parameter values as the airstream velocity increased.

The D_vo.x parameter values produced by the rotary atomizers increased as the liquid flow rate increased, and as the rotation rate and airstream velocity decreased, and were lower for the insecticide than for water. The slotted rotary drum atomizer gave the best control over droplet size, generally producing mono‐modal droplet size spectra where the other atomizers often produced bi‐ and multimodal spectra.     

Utilizing vortex behaviour to minimize drift

Abstract

The ULV spray emitted from a TBM flying in a cross wind was mapped by a scanning lidar system. The fate of the spray cloud for 2 min after release from the aircraft was followed as the material was transported downwind of the flight line. Vertical scans at 6 s intervals with 1 m^‐3 resolution provided detailed insight into the entrainment of the spray into the wing‐tip vortices and ultimate release to drift or deposit. Relative concentration, dosage and deposit profiles are presented for this cross‐wind case. Vortex lifetimes were found to be significantly different for the up‐wind and downwind vortices. The majority of the near field deposit was associated with the up‐wind vortex while the drift was linked to the down‐wind vortex.     

Pesticide concentrations in agricultural storm drainage inlets of a small Swiss catchment

Agricultural pesticides transported to surface waters pose a major risk for aquatic ecosystems. Modelling studies indicate that the inlets of agricultural storm drainage systems can considerably increase the connectivity of surface runoff and pesticides to surface waters. These model results have however not yet been validated with field measurements. In this study, we measured discharge and concentrations of 51 pesticides in four out of 158 storm drainage inlets of a small Swiss agricultural catchment (2.8 km²) and in the receiving stream. For this, we performed an event-triggered sampling during 19 rain events and collected plot-specific pesticide application data. Our results show that agricultural storm drainage inlets strongly influence surface runoff and pesticide transport in the study catchment. The concentrations of single pesticides in inlets amounted up to 62 µg/L. During some rain events, transport through single inlets caused more than 10% of the stream load of certain pesticides. An extrapolation to the entire catchment suggests that during selected events on average 30 to 70% of the load in the stream was transported through inlets. Pesticide applications on fields with surface runoff or spray drift potential to inlets led to increased concentrations in the corresponding inlets. Overall, this study corroborates the relevance of such inlets for pesticide transport by establishing a connectivity between fields and surface waters, and by their potential to deliver substantial pesticide loads to surface waters.

     

Penetration of soil dust through woven and nonwoven fabrics

Abstract

Several types of fabrics were laboratory‐tested for their effectiveness in worker protection to pesticide‐laden dust encountered in the agricultural environment. Of the applied <100 mesh dust, penetrations through knitted jersey and woven fabrics were greater than 87% and less than 5.8%, respectively. Treatment of woven fabrics with fluorocarbon polymers curtailed penetration by greater than 60%. Nonwoven fabrics allowed less than 0.5% dust penetration. Parathion mixed with 100‐mesh sieved dust resulted in increasing “ppm”; levels with decreasing particle size; extent of parathion conversion to paraoxon was independent of particle size for the sandy loam dust used.     

Drop size-dependent S(IV) oxidation in chemically heterogeneous radiation fogs

Six radiation fog episodes were sampled in the Central Valley of California during winter 1998/1999. Drop size-resolved fog samples were sampled using a size-fractionating Caltech active strand cloudwater collector (sf-CASCC). The sf-CASCC collects a large fog drop sample, comprised mainly of drops larger than 17 μm diameter, and a small fog drop sample, comprised mainly of drops with diameters between 4 and 17 μm. The fog pH was found to vary between approximately pH 5.3 and 6.8, with the pH of the large fog drop sample typically several tenths of a pH unit higher than the simultaneously collected small fog drop sample. At these high pH values, dissolved sulfur dioxide can be rapidly oxidized by a variety of chemical pathways and also can react quickly with dissolved formaldehyde to form hydroxymethanesulfonate. The amount of sulfate produced by aqueous-phase oxidation during each fog episode was determined by application of a tracer technique. The ratio of large : small drop S(IV) oxidation was compared with theoretically predicted ratios of large : small drop S(IV) oxidation rates. Although the higher pH of the large fog drops should promote more rapid S(IV) oxidation by ozone, finite rates of mass transport into the large drops and an increasing rate of complexation of S(IV) by formaldehyde at high pH combine to depress theoretically predicted rates of aqueous sulfate production in large fog drops below rates expected for small fog drops. This prediction is supported by the tracer results that indicate the concentration of sulfate resulting from aqueous-phase S(IV) oxidation in small drops generally exceeded the concentration formed in large drops. These findings stand in sharp contrast to observations in acidic clouds at Whiteface Mountain, New York, where hydrogen peroxide was determined to be the dominant S(IV) oxidant and the rate of S(IV) oxidation was found to be independent of drop size.     

Studies on the residues of phosalone on chilli by GLC after multiband plate cleanup

Abstract

Four sprays of 0.05 ana 0.10% phosalone were given on chilli (Capsicum annuum Linn.) crop at an interval of 15 days starting from 21 days after transplanting. Residues were determined in the green chilli fruits by GLC after cleanup of extract on multiband thin‐layer plate. The half‐lives of residues were 1.55 and 1.68 days on chilli fruits from the crop treated with four sprays of 0.05 and 0.10% phosalone respectively. The time required to reach the tolerance limit of 1 ppm after last spray with 0.05 and 0.10 % emulsion was 4.75 and 7.62 days respectively. Washing of fruits under tap water was found effective in bringing down the level of phosalone residues by 21.64 to 75.11 %.     

Atmospheric loss of pesticides above an artificial vineyard during air-assisted spraying

A procedure to assess pesticide emission to the air and characterise possible air pollution sources was carried out using a tracer dye and 2 mm PVC lines during air-assisted spraying of an artificial vineyard. Three experiments were performed to evaluate the method feasibility, quantify upward movements of sprayed droplets and investigate the influence of microclimatic variables on pesticide emission. During each experiment two test series were carried out with two droplet size distributions (very fine and fine spray, according to the BCPC classification). The amount of sprayed liquid collected at 2.5 m above ground varied between 9.0% and 10.7% of the total dose applied for very fine spray and between 5.6% and 7.3% for fine spray. In stable atmospheric conditions the spray drifted along the mean wind direction over the crop whereas in unstable conditions the sprayed liquid plume was larger, with a greater amount of material sent to higher levels. A statistical model based on a simple multiple regression featuring droplet characteristics and microclimatic variables (wind speed, temperature, stability parameter and relative humidity) provided a robust estimate of spray loss just above the crop, with an acceptable determination coefficient (R²=0.84). This method is therefore suitable for quantifying spray drift and provides a way to study the influence of several variables on the amount of pesticide released into the atmosphere by air-assisted spraying, with suitable accuracy.     

Phosmet residues in an orchard and adjacent recreational area

Two cover sprays of phosmet were applied to an orchard adjoining a camping area and a bird sanctuary with a resident goose population. Insecticide residues were monitored on orchard leaves, orchard ground cover, ground cover in the camp-site and along the adjacent lakeshore. Despite attempts to minimize drift, significant spray residues were found outside the target area. Residues on ground cover and leaves were reduced by sprinkler irrigation subsequent to spray application.