Managing the Ruellia erinose mite on Ruellia simplex Wright (Lamiales: Acanthaceae) cuttings using horticultural oil dip treatments

Ruellia simplex Wright, known as Mexican petunia, is primarily propagated through cuttings in nurseries and planted in ornamental landscapes. The aesthetic appeal of R. simplex is diminished by infestations of the eriophyoid mite, Acalitus simplex Flechtmann et Etienne. This mite induces open galls, called erinea. While integrated pest management (IPM) strategies have been established to manage A. simplex on potted plants, tools for controlling infestations on cuttings are poorly understood. This study assessed the efficacy of 4 formulated horticultural oils or oil blends: (i) rosemary oil, (ii) mineral oil, (iii) a blend of peppermint oil, clove oil, and sodium lauryl sulfate (blend 1), and (iv) a blend of castor, rosemary, clove, and peppermint oils (blend 2). These oils were evaluated for their control of A. simplex using 2 dipping approaches: (i) curative, with infested cuttings exhibiting erinea and (ii) prophylactic, with uninfested cuttings prior to erinea formation. Curative and prophylactic dips in mineral oil significantly controlled A. simplex by reducing and preventing new erinea formation. Blend 2 was effective in curative dips but not in prophylactic dips. Blend 1 and rosemary oil did not differ from the water or untreated cuttings in the curative dips; however, blend 1 demonstrated higher efficacy in the prophylactic dips compared to rosemary oil, water, and untreated cuttings. None of the evaluated horticultural oils caused phytotoxicity. These findings introduce a sustainable IPM tool to preserve the marketability of R. simplex cuttings, providing nurseries with an effective approach for managing A. simplex infestations during early propagation.