Hollingsworth, R.

Mc Donnell, R.

Millar, J.

Paine, T.

Undetermined

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14  Section I: Invasive Pests, Emerging Pests, and Hot Topics of Interest   CLOVE BUD OIL AS A NOVEL MOLLUSCICIDAL DRENCH FOR POTTED PLANTS R. Mc Donnell1, R. Hollingsworth2, J. Millar3, and T. Paine3 1 Dept of Crop and Soil Science, Oregon State University, Corvallis OR 97331 2 USDA-ARS-PBARC, 64 Nowelo Street, Hilo, Hawaii 96720 3 Dept of Entomology, University of California, Riverside CA92521 rory.mcdonnell@oregonstate.edu, robert.hollingsworth@ars.usda.gov, jocelyn.millar@ucr.edu, timothy.paine@ucr.edu  The horticultural trade is an important pathway for the introduction and spread of invasive gastropods (Cowie and Robinson 2003; Robinson 1999) because potted plants are essentially a portable microhabitat that protect snails and slugs, especially buried eggs and juveniles, from desiccation and molluscicides. The identification of an efficacious dip treatment would therefore be an important development in helping to manage this pathway. One such option is the use of essential oils, which have received a lot of research attention as novel pesticides over the past two decades (Batish et al. 2008) but their potential efficacy against terrestrial snail and slug pests has been largely overlooked.  In this study the molluscicidal potential of eleven essential oil emulsions (bitter orange, cedarwood, cinnamon, clove bud, eucalyptus, garlic, lemongrass, peppermint, pine, rosemary, spearmint) and one terpene (D-Limonene) were tested in laboratory and greenhouse trials as potential drench treatments for potted plants infested with the eggs and juveniles of the quarantine terrestrial snail pest, Cornu aspersum (=Helix aspersa). Clove bud oil (LC50: 0.027%) was most toxic (Table 1), followed by pine (LC50: 0.082%) and spearmint (LC50: 0.103%). In phytoxicity studies with Hosta ‘Royal Standard’ clove bud oil showed no apparent toxicity to the test plants at concentrations that caused 100% snail mortality.   Table 1. LC50, and corresponding 95% fiducial limits (FL) for the seven most toxic essential oil emulsions tested against Cornu aspersum (modified from Mc Donnell et al. 2016).  Oil N LC50 (%) 1 95% FL (%) Cinnamon 22 0.157a,b,c,d 0.128 - 0.206 Clove bud 19 0.027a,e,f,g,h,i,j 0.019 - 0.031 Garlic 23 0.115e,k,l 0.067 - 0.158 Lemongrass 23 0.160f,m,n,o 0.147 - 0.176 Peppermint 13 0.140g,k,p,q,r 0.126 - 0.155 Pine 17 0.082b,h,m,p,s,t 0.075 - 0.090 Spearmint 26 0.103c,i,n,q,s,u 0.092 - 0.119 1 Values with the same lowercase letters indicate statistically significant differences (P<0.05). These differences were determined by comparing the fiducial limits of each oil, i.e., statistically significant differences exist when there is no overlap between the fiducial limits.  The development of a biorational drench that is lethal to quarantine species such as C aspersum without damaging plants represents a significant advance in the development of novel tools for disinfesting potted plants. However, in order for a new molluscicide to be voluntarily adopted on a 15  wide scale it must be both lethal to the target pest and cost effective. Clove bud oil drenches are more expensive than current molluscicidal baits but have a number of distinct advantages. For example, some molluscicides often only inhibit feeding whereas clove bud oil drenches cause rapid mortality (< 24 h) of eggs and juveniles buried in soil and of juveniles on the soil surface. This is important from a quarantine perspective because the presence of a single living snail in a pot can be sufficient to cause rejection of an entire shipment. Furthermore, clove bud oil, like most essential oils, is pleasant smelling and non-toxic to humans. Thus the U.S. Environmental Protection has listed clove bud oil as exempt from pesticide registration requirements and pesticide residue tolerance requirements under section 25(b) of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). Such an exemption would greatly reduce the cost and time required for bringing a new pesticide containing clove bud oil to market. Also, because clove bud oil is a nontoxic product from botanical sources, it should qualify to be used as an organic pest control tool.   Acknowledgements We are grateful to the Western Region IPM Center which funded this research under grant 2007-51120-03885. The data presented in this report are adapted from Mc Donnell et al. (2016). For copies of this publication please contact Rory Mc Donnell (rory.mcdonnell@oregonstate.edu).  References Batish DR, Pal Singh H, Kumar Kohli R, Kaur S (2008) Eucalyptus essential oil as a natural pesticide. Forest Ecol and Manag 256:2166-2174. Cowie RH, Robinson GD (2003) Pathways of introduction of non-indigenous land and freshwater snails and slugs. In: Ruiz GM and Carlton JT (eds) Invasive species. Vectors and management strategies. Island Press, Washington, pp 93-122. Mc Donnell RJ, Yoo J, Patel K, Rios L., Hollingsworth R., Millar J., Paine T. (2016) Can essential oils be used as novel drench treatments for the eggs and juveniles of the pest snail Cornu aspersum in potted plants? J Pest Sci 89:549-555. Robinson DG (1999) Alien invasions: the effects of the global economy on non-marine gastropod introductions into the United States. Malacol 41:413-438.           

Clove Bud Oil As A Novel Molluscicidal Drench For Potted Plants

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Clove Bud Oil As A Novel Molluscicidal Drench For Potted Plants

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