Evaluation of Artemisia vulgaris Essential Oil–Kaolin Combinations as Repellents against Diaphorina citri

Abstract

Citrus Vein Phloem Degeneration (CVPD) is a destructive citrus disease associated with Candidatus Liberibacter asiaticus, a bacterium belonging to the class α-proteobacteria. Psyllid vectors, primarily Diaphorina citri, transmit the pathogen by acquiring and inoculating the bacterium directly into the phloem tissues of citrus plants. This study aimed to evaluate the repellency of different concentrations and combinations of kaolin and Artemisia vulgaris essential oil against D. citri. The research was conducted at the Plant Protection Laboratory and Experimental field, Faculty of Agriculture, UPN Veteran Yogyakarta. The experiments employed choice and non-choice tests arranged in a completely randomized design. The treatments consisted of different concentrations of A. vulgaris essential oil combined with kaolin. The 2% A. vulgaris essential oil and 1.5% kaolin combination showed a repellency index of 0.66 against D. citri after 12 hours in the non-choice test, indicating a repellent effect. In the choice test, the combination treatment resulted in 6.83-7.66 D. citri moving toward untreated twigs during the 20-60 minute observation, suggesting that the repellency was primarily associated with the volatile compounds released from A. vulgaris essential oil and was enhanced by the presence of the kaolin film. In the persistence test, repellent activity remained evident one day after application but declined progressively from 60% after 1 day to 7 and 14 days after application, likely due to the volatilization of A. vulgaris essential oil. The treatment did not adversely affect citrus growth and even resulted in better growth than untreated plants, although kaolin residue may reduce light intensity received by the plants. These findings indicate that combining A. vulgaris essential oil with kaolin has potential as a botanical-based repellent strategy to reduce D. citri activity in citrus production.