Optimizing spirotetramat applications for effective onion thrips control in bulb and green onions

Onion thrips, Thrips tabaci Lindeman, (Thysanoptera: Thripidae) is the most significant pest of Alliums (Amaryllidaceae) and is primarily managed with insecticides. Spirotetramat, a systemic insecticide, is currently recommended for early season use in bulb onion production, but its residual effects based on application timing, frequency, and plant age are poorly understood. From 2016 to 2023, we conducted a series of trials assessing the impact of these factors on thrips control. We compared 2 application timings and frequencies on onion thrips management in bulb onions. Finally, we conducted a separate green onion experiment, altering plant age and application frequency to determine the effect on onion thrips populations and spirotetramat uptake by the plant. Our results showed that 2 sequential applications of spirotetramat reduced onion thrips densities by 50%, but application timing had no impact on thrips densities in both bulb and green onions. Green onions that received 2 applications of spirotetramat had significantly higher spirotetramat levels in the leaf tissue than those treated once. In green onions, more spirotetramat was detected in young plants compared with older ones, and there was a negative correlation between spirotetramat levels in leaf tissue and onion thrips densities on plants. Overall, our results indicated that 2 applications of spirotetramat are necessary for effective onion thrips control on bulb onion and green onion, likely due to increased insecticide levels in plant tissue.