Chitosan as a rainfastness adjuvant for agrochemicalsElectronic supplementary information (ESI) available: Exemplary proton NMR spectrum for chitosan, table of molecular weight data for polymers, table from the BBCH handbook of plant growth scales and figure detailing concentration of azoxystrobin as detected by LC-MS/MS. See DOI: 10.1039/c6ra23485b

Chitosan has been identified as an excellent rainfastness aid for a model agrochemical. We use fluorescent labelling and microscopy to show that chitosan deposits on Vicia faba leaves are able to resist wash off by rain, both in a lab-scale test and via simulated rain. Furthermore, via the same methods it has been demonstrated that the rainfastness of azoxystrobin, a common fungicide which is fluorescently active, can be improved by formulating with chitosan. These findings via fluorescent microscopy were in agreement with a quantitative LC-MS/MS method in which the exact quantity of active ingredient on a leaf surface was determined before and after a rain wash. The potential of chitosan as a rainfastness aid is further supported by positive comparison with a commercial tank-mix standard, with almost 100% retention of the model active ingredient achieved in both cases after 1 hour of washing with 10 mm h −1 intensity rain. Chitosan has been identified as an excellent rainfastness aid for a model agrochemical.