We investigated citric acid as a potential molluscicide and deterrent for the invasive slug species Arion fasciatus (Nilsson, 1823). To examine the efficacy of citric acid through ingestion or environmental exposure, slugs were given lettuce sprayed with 5% citric acid or 5% citric acid sprayed paper towels in no-choice tests. Slugs in choice tests were given both Romaine lettuce sprayed with 5% citric acid and DI water. We also investigated the impact of spraying Romaine lettuce seedlings with 5% citric acid to see if it impacts plant growth. No-choice tests revealed that environmental exposure to citric acid resulted in the eventual death of 64% of the slugs in the treatment group, while the ingestion of citric acid did not affect slug mortality. Choice tests revealed that citric acid significantly decreased Romaine lettuce herbivory. Romaine lettuce seedlings that were sprayed weekly for six weeks with 5% citric acid had a 31% lower biomass compared to the control, but no seedling deaths were observed. Overall, citric acid shows promise as a slug deterrent and molluscicide, though greenhouse and field trials are required to further elucidate its efficacy and impact on plants.