2012 Annual Report
Export of ornamental plants are high risk for pest species of slugs and snails because their eggs and juveniles can hide within the planting medium of potted plants. Pre-harvest control practices for slug and snail control in potted plants include removal of hiding places, weed control in the nursery, keeping infested and uninfested plants separate, and using molluscicide baits. While these practices are helpful, they are frequently not sufficient to achieve quarantine security, which requires complete exclusion of pests. We tested the efficacy of eleven essential oils and one terpene chemical for control of eggs and juveniles of slugs and snails. In Petri dish bioassays, seven essential oils (pine, lemongrass, clove, spearmint, garlic, peppermint and cinnamon) were determined to be highly effective (100% mortality) against eggs and juveniles of the European Brown Garden Snail (Cantareus aspersus) and eggs of Amber Snails (Succinea spp.) at a 1% concentration. For eggs of the Cuban slug (Veronicella cubensis) and the giant African snail (Lissachatina fulica), hatch was completely inhibited by a 24-hour exposures to 1% concentrations of cinnamon, lemongrass, peppermint, or pine oils. We quantified the toxicity of these oils using probit analysis to calculate. Clove oil proved to be the most toxic to C. aspersus juveniles and was 3 times as toxic as the next most effective oil (pine oil). To validate these results in a setting more closely simulating field conditions, juvenile C. aspersus were placed in mesh bags and then placed on the surface or buried at a depth of 2.5 cm in pots containing potting media. We also buried eggs held in mesh bags at the same depth. Two treatment concentrations of clove oil were used. The results showed that 100% mortality of eggs and juveniles was achieved at 0.116% after exposure periods of 1 or 3 days. Drenches of clove bud oil at 0.116% and 0.50% completely controlled juveniles and eggs, respectively, of Parmarion martensi, the Asian semi-slug. Finally, to test for potential phytotoxicity we drenched the leaves and the soil of Gardenia jasminoides with 0.116% clove oil solution. No phytotoxic symptoms were observed on the leaves or roots of test plants over the course of 1 week. Our research will likely lead to the development of new commercial molluscicide products containing essential oils as the active ingredients. The EPA exempts certain active ingredients from pesticide registration and residue tolerance requirements. These exempted ingredients include oils from cinnamon, garlic, peppermint and clove. This exemption dramatically reduces the cost and time required for bringing a new pesticide to market.