Agrochemical Spray Droplets -
Localisation of Co-formulants in Deposits
and Transport Across Plant Surfaces

Abstract

Crop protection strategies frequently utilise crop protection formulations (commonly termed pesticides). These formulations, consisting of active ingredients (AIs) and adjuvants, can be sprayed onto a plant surface to target specific pests. A good understanding of the association of the AIs and adjuvants in pesticide droplets is required to
increase the efficacy of pesticide development. This thesis details experimental work aimed at improving the current understanding of the relationship between AIs and adjuvants in pesticide droplets, their phase behaviour, and localisation within a pesticide deposit.

Following initial Raman spectroscopic characterisation of the AIs and adjuvants supplied by Syngenta, various aqueous model systems were created using the AI Fomesafen
and either Brij O10 or a range of poloxamer adjuvants. Nanolitre sized droplets of the model systems were printed onto hydrophobised model silicon and glass substrates,
and droplet evaporation dynamics and deposit morphologies were characterised. The extent of droplet pinning during evaporation was found to differ depending on the AI
and adjuvant combinations, with control over droplet pinning found possible through addition of Brij O10 in small amounts (0.02 w/v %) to a poloxamer-Fomesafen system.

An experimental methodology was created to map the location of AI and adjuvant across droplet deposits on model hydrophobic silicon substrates. Raman spectroscopy
was used in conjunction with the chemometric technique factor analysis (FA), to obtain weightings of the relative amounts of AI and adjuvant located at positions across
a droplet deposit. It was possible to use this methodology to obtain weightings where the AI and adjuvant were co-located throughout the deposit (Brij O10 + Fomesafen
and poloxamer + Fomesafen model systems), in addition to when phase separation of the system components occurred (ammonium sulphate + sodium lauryl ether sulphate
model system).

A total internal reflection (TIR) Raman spectroscopy experimental rig was set-up to
study the movement of AIs and adjuvants across living plant surfaces. TIR Raman
data was collected detailing the movement of Fomesafen and/or Brij O10 into a leaf, over the course of 22 hours, for leaf samples cut from a Clivia plant or on a living Clivia plant. The FA method was adjusted and used to analyse the data. Initial results obtained indicate differences in uptake of Fomesafen depending on whether Brij O10 was
present. Additionally, results differed depending on whether a living plant surface or a cut-out section of leaf was used. Overall, TIR Raman presents as a promising technique
for analysing AI and adjuvant movement on living plant surfaces.