Little is known about the performance of bioinsecticides in combination with adjuvants approved for organic onion production. To address this issue, two studies were conducted in 2018 and 2019: 1) combinations of four bioinsecticides (Isaria fumosorosea Apopka strain 97, azadirachtin + pyrethrins, azadirachtin, and spinosad) and three adjuvants (pinene polymers, potassium salts of fatty acids, and neem oil) in field trials in New York and Wisconsin, and 2) the same four bioinsecticides co-applied with neem oil as an adjuvant in field trials in New York. In both studies, spinosad was the most effective bioinsecticide, providing the largest reductions in thrips densities (26–85%) and feeding damage (56–69%) and the largest increases in total onion yield (10–26%) compared with the untreated control. Co-applications of spinosad with either neem oil or salts of fatty acids more effectively reduced thrips densities compared with co-applications of spinosad and pinene polymers; however, onion yield was similar regardless of the adjuvant used with spinosad. Isaria fumosorosea Apopka strain 97 and the premix of azadirachtin + pyrethrins did not control thrips. Implications of our results underscore the importance of evaluating the performance of insecticide and adjuvant combinations for optimizing pest management.