The retention and distribution of spray droplets within the plant canopy have a crucial effect on the biological efficacy of pesticides To maximise spray retention droplets that impact a leaf must remain on the plant Three outcomes are possible when a droplet impacts a leaf surface adhesion bounce or shatter Those droplets that bounce or shatter can continue their journey through the canopy depositing at lower levels in the canopy or on the ground Mathematical models based on the physical processes involved in the bounce/ adhesion and shatter of droplets have been developed improved and described These processbased retention models have recently been implemented within an experimental build of the spray application simulation software AGDISP This has allowed differences in total spray retention to plants due to the spray formulation used or vegetative species studied to be predicted This paper discusses these new tools illustrates the effect different spray formulations and application parameters have on predicted retention and compares model predictions with measured retention

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Invasive species such as insects, pathogens, and weeds reaching new environments by traveling with the wind, represent unquantified and difficultto-manage biosecurity threats to human, animal, and plant health in managed and natural ecosystems. Despite the importance of these invasion events, their complexity is reflected by the lack of tools to predict them. Here, we provide the first known evidence showing that the long-distance aerial dispersal of invasive insects and wildfire smoke, a potential carrier of invasive species, is driven by atmospheric pathways known as Lagrangian coherent structures (LCS). An aerobiological modeling system combining LCS modeling with species biology and atmospheric survival has the potential to transform the understanding and prediction of atmospheric invasions. The proposed modeling system run in forecast or hindcast modes can inform high-risk invasion events and invasion source locations, making it possible to locate them early, improving the chances of eradication success.

Abstract. An experiment was undertaken to test the hypothesis that AGDISP, a mechanistic model that simulates the landing position of droplets aerially released for pesticide application, overestimates downwind airborne spray concentrations by not accounting for the turbulence generated within the canopy sublayer. AGDISP is used by pesticide regulators in many parts of the world to quantify exposure from aerial pesticide spraying as part of an assessment of risks to public health and the environment. Using a novel design, airborne spray drift was measured in a 3.2 m high radiata pine plantation, 65 m downwind from the aerial spray flight line, using a small circular sampling array. The spray sampling array consisted of a central 10 m high mast plus a set of 16 secondary masts distributed evenly around a circle with a radius of 5 m from the central mast. All spray applications were made with a Bell Jet Ranger using a spray mix of water plus a fluorescent tracer and a droplet spectrum with a volume median diameter of 101 µm. A single treatment comprised six passes along the flight line, and there were 28 replications. Airborne spray was sampled with both rotorods and artificial foliage placed at four heights on the central mast, ranging from approximately half canopy height to 3 times canopy height. The secondary towers sampled airborne spray using the same collectors placed at just above canopy height and at half canopy height. Other measurements included leaf area distribution, prevailing meteorological conditions, and turbulence using sonic anemometers. Backscatter LiDAR was used in an attempt to quantify the height and density of the spray cloud in the vicinity of the central mast. Rotorod and artificial foliage deposition values were highly correlated, giving confidence in the sampling approach. Neither wind speed nor release height had a significant effect on airborne spray flux in the 0 to 10 m zone, but results were complicated by a spurious negative correlation between wind speed and spray release height. The lack of dependence of deposition on wind speed in this experiment is surprising but is explained both by the variance in the data as well as the physics of small droplet movement in the atmosphere. At the individual sample level, measurements of airborne spray using either rotorods or artificial foliage were poorly correlated with AGDISP predictions. However, when data were averaged across replications, there was a very strong correlation between measurements and AGDISP data, even though in absolute terms, and as hypothesized, AGDISP significantly overpredicted the quantity of airborne spray. As indicated from a comparison with measured deposition, the backscatter LiDAR appeared effective in describing the spray cloud profile, and it suggested a total spray cloud profile that was more complex than the AGDISP model prediction. Keywords: Aerial application, AGDISP, Canopy deposition, Pesticides, Spray drift.

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