Evaluating combinations of bioinsecticides and adjuvants for managing Thrips tabaci (thysanoptera: Thripidae) in onion production systems

ABSTRACT 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.