Development of bio-adjuvants for conventional and organic farming.

Smith, Kellie and Roberts, Mike and Coogan, Michael and Holroyd, Geoff and Adkins, Gary (2019) Development of bio-adjuvants for conventional and organic farming. Masters thesis, Lancaster University.

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Abstract

Developing bio-adjuvants for use in commercial and organic farming. Adjuvants help improve the targeting, retention, penetration and overall activity of a pesticide used in foliar application, as a form of pest control. It is important to understand adjuvants and their modes of action to improve application success rates and reduce environmental impact of pesticides. Both a traditional organosilicone surfactant and a range of bio-adjuvants were compared, using methods to study droplet behaviours on the leaf surface of the monocot, Commelina communis. Droplet lifetimes were quantified when droplets were no longer visible on the leaf. Drying times of droplets typically increased with droplet volume, but this response varied between adjuvants. The surfactant had a shorter retention than all bio-adjuvants with a range of different actives. A paraffin wax-based adjuvant exhibited consistently longer drying times than other adjuvants and water, with a range of actives. Adjuvants formulated with different pesticides (e.g. fungicide, insecticide or biofungicide), had a significant effect on the droplet lifetime behaviours of different adjuvants when used with water alone. These results demonstrate the need to understand how adjuvants and actives interact, before recommendation for their application. Droplet areas of most adjuvants were larger than water, meaning they were able to enhance spreading over the surface. The percentage leaf area coverage achieved by different adjuvants was compared using spray application with a pesticide. The coverage varied significantly between adjuvants, but the bio-adjuvants had better coverage than the surfactant. One glycolipid, oil-based adjuvant gave significantly higher coverage of pesticide on the leaf than water and all the other adjuvants. Penetration experiments using a range of fluorescent techniques, were inconclusive determining which adjuvant could best facilitate penetration of a fluorescent tracer dye or a fluorescent active ingredient into the C. communis leaf. For application in organic farming, the adjuvants had some negative effects on the growth of Gliocladium catenulatum biofungicide relative to water control. The carbohydrate-blend gum adjuvant had the most severe effects on biomass compared to water and other adjuvants. These data can be used to inform growers of which bio-adjuvant to use when high moisture retention or good coverage is required for a given pesticide. Further field trials will help to screen adjuvants which may be compatible with biopesticides and assess effects on biocontrol.