Associating Fresh-market Blackberry Size and Composition with Detachment Force to Develop Robotic Harvesting Solutions

Renee T. Threlfall, Anthony L. Gunderman, Amanda L. McWhirt, W. Rudd, Zachary Bean, Dathan Vaught, Benjamin Sowden

Robotic technologies are being developed to aid rapid and gentle harvest of fresh-market blackberries ( Rubus L. subgenus Rubus Watson). Berry size and composition and their relationship to detachment force were followed to inform robotic harvesting design. For each of the four blackberry cultivars, fruit was harvested from two rows (>120 berries/row) and two harvests (1849 blackberries total) in 2025. Detachment force, berry size (weight, length, and width), and berry composition (soluble solids and pH) were influenced by cultivar. ‘Sweet-Ark ® Caddo’ (2.27 N) and ‘Von’ (2.26 N) had the highest detachment force followed by ‘Ouachita’ (2.12 N), then ‘Sweet-Ark ® Ponca’ (1.95 N). Of the berry size and composition attributes evaluated, only pH (r = −0.29) was most related to detachment force, regardless of cultivar. Generally, as pH increased, detachment force decreased in all cultivars, more significantly than with berry weight or soluble solids. This study provided insight on the associations between detachment force, with berry size and composition attributes and served to build datasets to inform development of robotic solutions for harvesting.