Combination of Essential Oils and Kaolin to Control Psyllids

Daniel Cooper HLB Management, Tip of the Week

By Xavier Martini and Romain Exilien 


Despite intensive control efforts, the Asian citrus psyllid (ACP), the vector of Candidatus Liberibacter asiaticus, the bacteria causing citrus greening, remains the most devastating pest of citrus.

essential oils

The ACP typically relies on tactile, visual and odor cues to detect its host. By combining an irritant, a visual masking and a true repellent, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers aim to significantly repel ACPs from citrus. They tested the use of kaolin with food colorant as an irritant and visual masking, and the combination of essential oils as odor repellents with kaolin.


When ACPs were given a choice between uncoated and kaolin-coated plants, a significant number of the pests chose the uncoated plants over those coated with kaolin. Fewer ACPs settled on plants coated with red kaolin than on those coated with kaolin. In contrast, the number of ACPs settled on blue and white kaolin-coated plants was not different.

Subsequently, an additive effect of thyme and kaolin was observed as fewer ACPs were found on plants coated with thyme and kaolin than on plants coated with kaolin only. These findings suggest the possible use of red-colored kaolin and/or the combination of thyme and kaolin as a means of reducing ACPinfestation in citrus.

This therapy has not yet been tested in the field. However, if a grower is already using kaolin, it will not hurt to add essential oil to improve the efficacy of it.


  • Kaolin dyed with red food colorant is more repellent against ACPs than white kaolin. 
  • Kaolin and thyme oil mixed have an additive effect against ACPs. 
  • The combination of kaolin with colorant and/or essential oils may provide an alternative control strategy for organic and conventional growers. 

Acknowledgment: This research is funded by the U.S. Department of Agriculture National Institute of Food and Agriculture.

Xavier Martini is an assistant professor, and Romain Exilien is a pre-doc fellow, both at the UF/IFAS North Florida Research and Education Center in Quincy. 

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