Drift Reduction Technologies Andrew Hewitt
DRTs • Systems that avoid “Fines” being sprayed (nozzles, tank mixes) • Systems that avoid “Fines” forming through evaporation (anti- evaporants) • Minimizing the effective spray release height (lower the boom or add a shield/ shroud/ air curtain) • Moving the droplets faster toward the target (optimized velocity/ trajectory/ electrostatic charge) • Targeted spraying (sensors, directional spraying etc)
Avoiding Spray Drift Exposure the “Easy” Way • Don’t spray small droplets (<~100-150 µm) Droplet Diameter Fall velocity (m/s) Drift distance (micrometers) Downwind (m) 10 0.003 1000 30 0.027 111 100 0.25 12 300 1.2 2.5 1000 5.0 0.6
Avoiding Spray Drift Exposure the “Hard” Way • If there are some “Fines” in the spray, there can be some mass of the applied spray that can move off-target under unfavourable conditions (physical and air shields can help reduce this, e.g. hoods) • The movement and deposition of these “Fines” will depend on many factors and variables associated with the particle size/ velocity/ shape spectrum, application technique, boom height, sprayer wake/ vortices, meteorological and atmospheric conditions, evaporation rate, canopy, barriers, electrostatic charge, etc.
4 1.5 70 µm 1.5 3.5 1.5 216 µm 1 3 1 1 0.5 2.5 0.5 0.5 2 0 0 0 0 0.05 0.1 0.15 0.2 1.5 0 2 4 6 8 0 0.1 0.2 0.3 Turbulence intensity * Turbulence intensity Wind Speed (m/s) 1 0.5 0 1.5 1.5 0 200 400 600 1 1 Droplet Size (VMD) (µm) 0.5 0.5 0 0 0 20 40 60 0 50 100 150 4 Temperature (deg C) Relative Humidity (%) 3.5 3 2.5 2 1.5 1.5 1 1 0.5 0.5 0 0 0 50 100 0 10 20 Speed (m/s) Height (m) AgDRIFT Sensitivity analysis - effect of application parameters on spray drift deposition
Spray Dynamics • Spray dynamics are affected by nozzle type, energy input (e.g. spray pressure, rotation rate, air shear) and tank mix physical properties from the sum of all components of the tank mix, and are not always intuitive especially for non-Newtonian tank mixes • Many DRAs improve the droplet size spectrum even with the better nozzles by “fine-tuning” the “Fines”
Assuring good coverage is important • Adjuvants can help with spread/ retention/ uptake as well as improving the droplet size spectrum – i.e. dual benefits possible with optimized systems and when paired with the best application system (e.g. nozzle) • Some adjuvants increase, and others reduce, spray angle with some nozzle types. If an adjuvant reduces the spray angle, do we need to use it with a wider angle nozzle such as some of the newer 140 degree types?
Application for Efficacy without Losses Such as Drift is Complex – Modeling Helps • Spray dynamics affect total spray performance and we cannot only consider efficacy – we also need to avoid losses such as drift • Good efficacy requires good coverage. This is affected by spray dynamics, sprayer speed, tank mix physical properties, leaf/ target characteristics, weather, etc. • What works well with one sprayer at one site may not work at another because conditions vary, as do sensitive areas • When we change formulation chemistry we can change not only droplet size but also the spreading and uptake • Formulation effects can vary widely with different nozzles, pressures, etc • By using spray dynamics and coverage data on each nozzle and tank mix, as well as levels of concern for drift risk assessment, we link with decades of modeling work to show spray performance both for coverage and for no-spray buffer zones, using regulatory approved models
Spray Calculators: The Database Component • Spray dynamics is much more than just droplet size. We also measure/ calculate many factors that are then used by the models, using accepted protocols/ standards to link with AGDISP: - Droplet density and air inclusions - Droplet size/ velocity profile - Droplet/ spray evaporation rates - Drift potential - Dynamic surface tension at temperatures and lifetime ages appropriate to a) atomization and b) retention/ spreading/ sticking/ uptake - For non-Newtonian liquids, viscosity parameters such as Trouton Ratio
Data Collection for Full Spray Dynamics
The Modeling Component • AGDISP Aerial and Ground models to put the spray dynamics into spray fate and drift context for each unique application scenario (e.g. for decision-making) and reasonable worst case scenarios (for risk assessment). Note: Ground Modeling is based on inputs from our work with regulators and industry to determine how to use the ground model with appropriate inputs such as droplet size Rosin-Rammler conversion; appropriate evaporation algorithms; nozzle model choice; etc. • Spray coverage modeling based on our research of droplet fate • L-Studio modeling for plant leaf and droplet interactions
Evergreen • Our approach is evergreen because we add new data sets as new formulations, nozzles etc are developed • Ditto for linking each pesticide toxicity for specific sensitive areas to show DRT performance in terms of actual no-spray buffer zone reduction • Validation work has covered ground and aerial applications. We also included an approach based on some regulatory preferences for drift potential based on sampling airborne drift flux in a wide wind tunnel • A key aspect of the work is the fact that drift reduction technology performance requires proof that a DRT does not adversely affect efficacy potential. The calculator shows this
DRT Testing • Field studies • Wind tunnel droplet size • Wind tunnel drift potential • Some registrants have conducted field studies to show the drift potential of their product with specific recommended nozzle(s) and then negotiated with EPA to cover tank mix partners through a standard protocol of testing with a nozzle such as TTI/ AIXR/ etc and then running data through AGDISP and approving those adjuvants that don’t increase the no-spray buffer zone size (or requiring a DRA with some adjuvants in order to be allowed) • Other approaches can use a range of nozzles and pressures appropriate to the application type
System Pressure (bar) Nozzle Type Exit orifice Type Nozzle F M C VC XC UC Hypro ULD120-04 6.0 4.5 2.5 Hardi ISO Minidrift 025 6.0 4.0 2.0 Single TeeJet AIC11025 6.5 4.5 2.5 Air induction TeeJet AIXR11002 6.0 5.0 2.5 1.5 TeeJet AI3070-02 4.0 2.0 1.5 Twin Hardi ISO Minidrift Duo 025 6.0 4.0 2.0 Single TeeJet TTI110015 7.0 3.5 Air induction - Anvil Twin TeeJet AITTJ60-11003 7.0 4.0 2.5 1.5 TeeJet TT11001 6.0 2.5 Single Anvil TeeJet TT11004 4.5 1.5 Twin TeeJet TTJ60-110025 6.0 4.5 1.5 Hardi ISO F-110 015 5.0 1.5 Single TeeJet TP11001 3.5 Flat fan TeeJet XR8003 4.0 1.5 Twin TeeJet TJ60-6503 4.0 2.0 Hollow cone Single TeeJet TX-18 5.0 Single Hardi ISO LD-110 025 5.0 2.0 Pre-orifice flat fan Twin TeeJet DGTJ60-11002 4.0 2.5
Conclusions • DRTs should be assessed in view of drift reduction (e.g. reducing Fines and showing buffer zone reduction through AGDISP modeling….or expensive field studies) AND coverage on the target • Spray calculators can support decisions for the huge numbers of nozzles, application rates, products, driving speeds, spray pressures, etc., complementing risk assessment with spray coverage on different targets for different conditions of spray dynamics
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