Adjuvant-enhanced acaricidal solutions to overcome foliar hydrophobicity for controlling the litchi erinose mite (Aceria litchii)

Litchi erinose mite (Aceria litchii) is the primary pest of litchi trees in several countries, causing yield losses of up to 80%. Mite infestations lead to the formation of a protective layer on leaves, known as erinose, which shields mites from various adverse factors, including contact with applied acaricides. This study aimed to evaluate the effect of adjuvants on the properties of acaricide solutions and their impact on A. litchii. Nine adjuvants (Aureo®, Break-Thru®, Fighter®, Fixer®, Iharaguen-S®, MSO Spray®, Orix AD®, Silwet L-77®, and Wetcit Gold®) and two acaricides [Sanmite® (pyridaben) and Ortus® (fenpyroximate)] were selected for investigation. Initially, key solution properties—surface tension, contact angle, and pH—were measured using a tensiometer for sprays containing acaricides alone and in mixture with adjuvants. Biological efficacy was evaluated in laboratory leaf-disc arenas sprayed with a Potter spray tower, with mite survival assessed 96 h after application. Among the tested acaricides, pyridaben was the most effective, resulting in fewer mites surviving and leaving the erineum. Additionally, the adjuvants Break-Thru®, Fighter®, Iharaguen-S®, Silwet L-77®, and Wetcit Gold® enhanced acaricide efficacy, particularly when combined with pyridaben.