Thrips species, population dynamics, and seed treatment effectiveness in dry beans

Dry bean (Phaseolus vulgaris L.) is an economically significant crop in the Midwest. Thrips can injure dry bean plants through feeding and oviposition on leaves and bloom, and their outbreaks often link to warm and dry springs. The pest status of thrips in this system remains poorly understood. Despite limited data on their actual economic impact on dry beans, neonicotinoid seed treatments and foliar sprays are frequently used, which leads to potentially unnecessary expenses and ecological disruption. This study evaluated thrips species composition, population dynamics, and thiamethoxam seed treatment effects on growth and yield of six dry bean varieties. Thrips were collected from sticky traps, whole plants, and bloom samples. Two key species, Frankliniella occidentalis and Thrips tabaci, were detected, with population peak occurring from late June to July. Both species were present during the vegetative stage, but F. occidentalis dominated during the reproductive stage. Variety ‘Eclipse’ had the highest whole-plant thrips counts, while ‘Rosie’ showed the highest bloom infestation. Seed treatment containing thiamethoxam and fungicides mostly had no significant effect on thrips population, plant biomass or yield across varieties, indicating the lack of benefits from the seed treatment. In addition, our results raised a concern on the efficacy of neonicotinoid seed treatments for thrips management in dry beans, which requires further research. Overall, this study enhances understanding of thrips in dry beans, providing growers with science-based insights to make informed decisions and reduce unnecessary pesticide use.