Degree

Doctor of Philosophy (PhD)

Department

The School of Plant, Environmental, and Soil Sciences

Document Type

Dissertation

Abstract

Giant salvinia (Salvinia molesta) is free-floating aquatic fern that originates from South America. Through human introduction, giant salvinia has escaped its native range and is listed as an invasive species across multiple continents causing negative socio-economic and environmental impacts. This research aimed to expand our understanding of integrated pest management for controlling giant salvinia by combining chemical and biological control. The objectives were to assess the effects of rainfastness, carrier volume, and growth stage on herbicide efficacy, assess augmented biological control and optimal weevil release densities, assess weevil populations in the field, determine herbicide and surfactant toxicity to weevils, investigate weevil movement off herbicide-treated plant material, and evaluate the salinity tolerance of salvinia weevils. Metsulfuron, glyphosate, flumioxazin and the combination of glyphosate +flumioxazin have a high rainfastness without the use of surfactants and no differences in herbicide efficacy among giant salvinia growth stages were observed. Metsulfuron and the combination of glyphosate + flumioxazin control did not differ among carrier volumes, but penoxsulam provided mixed results across carrier volumes. Salvinia weevils were more susceptible to direct exposure to modified vegetable oil surfactants than the herbicides metsulfuron, glyphosate, flumioxazin and the combination of glyphosate + flumioxazin, and were found to move off herbicide treated material after seven days. Recommended weevil release densities were not sufficient at controlling plants released with classical or augmented insect release approaches and changes to the method of harvesting weevils and release strategies should be made by increasing weevil densities and reducing the amount of plant biomass used to release weevils. Field sites in Louisiana contain suitable nitrogen for weevil establishment and factors like temperature and waterbody size could play a role in poor weevil establishment. Salvinia weevils can tolerate salinity levels of

Date

7-2-2026

Committee Chair

Webster, Lucas C.

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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