Plant Protection Chemistry NZ Ltd
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Fundamental R & D

How do agrichemical sprays applied to plants work? Their biological efficacy is related to the amount of spray retained by the plant, the area of foliage covered by the spray and/or how much active ingredient (AI) enters the plant (uptake) and moves (translocates) inside the plant to the site of biological action. PPCNZ is heavily involved in research to clarify the mechanisms involved in each of these processes and to model them. This fundamental research provides valuable IP to underpin all our application research.

Spray Retention

To maximise total spray retention to foliage, droplets that intercept with a leaf must remain on the plant. When a droplet impacts a leaf there are three possible outcomes: adhesion (the drop "sticks" on initial impact), bounce and shatter (see below). The rebounding (bouncing) or shattered droplets can be recaptured on the same leaf, or other leaves at the same leaf level, or continue their journey through the canopy depositing at lower levels in the canopy or on the ground.

 

This retention and distribution of spray droplets within the plant canopy has a crucial effect on the biological efficacy of pesticides. PPCNZ studies these individual processes (adhesion, bounce and shatter) as well as total retention, experimentally. We have also developed models based on experimental data for adhesion and retention. However, our more recent emphasis (currently in conjunction with Queensland University of Technology (QUT) and other International Industry partners) has been on the development and improvement of process-driven (driven by physical processes and their associated physiological parameters) models for adhesion, bounce and shatter. These have been implemented in different spray application simulation software packages (either in conjunction with QUT or Scion, a NZ Crown Research Institute) in order to predict spray retention. PPCNZ has an in-depth understanding of the consequence of the dynamic interactions of the formulants within the spray droplet during flight and on impact, physical properties of the droplet, leaf surface morphology, the interaction of leaf surface and formulation, as well as leaf orientation, on spray retention. View our publication list.

To determine formulation and species differences on spray retention we measure dynamic surface tension of the formulations, wettability of the leaf surface by static surface contact angles and advancing and receding contact angles of spray formulations on leaf surfaces.

Droplet Spreading
It is well known that surfactants modify the surface tension of agrichemical solutions, affecting the spreading of spray droplets on leaf surfaces, significantly influencing biological efficacy.
While PPCNZ has for decades determined the spread areas of different formulations on leaf surfaces and continues to do so, we have recently more fully explained the differences in spreading among surfactants, and the observations that surfactant solutions can spread quite differently on different leaf surfaces. We have developed a novel technique capable of isolating and quantifying both the physical (roughness) and the chemical polarity of the leaf surface. This has enabled us to determine the effect of adjuvant and leaf surface (roughness and polarity) character on droplet spread area. This research is ongoing, with process-driven models for spreading in development. View our publication list.

Foliar Uptake and Translocation of Active Ingredient (AI)
PPCNZ routinely studies the effect of different formulations on the uptake and translocation of pesticides in whole plants, primarily using 14C-radiolabelled AI. Although fundamental work has focused on spray retention, we have also studied extensively the mechanisms of uptake, and to a lesser extent translocation, developing simple empirical models. We have a solid understanding of the contribution of spray formulation components to foliar uptake. We are currently considering a more mechanistic interpretation of uptake in collaboration with Queensland University of Technology. View our publication list.

Biological Efficacy
PPCNZ studies the biological efficacy of herbicides under both laboratory (tracksprayer) and field conditions. We have a fundamental understanding of the influence of spray retention, spreading, uptake and translocation on biological efficacy and can provide evidence or reasons for differences in the biological efficacy observed among formulations utilising laboratory based studies.

 


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