Transplanting of micropropagated blackberry plugs in the field during late summer and early fall is a common nursery practice for commercial blackberry production. During this field transition, blackberry plants generally experience different stresses in addition to transplanting shock coupled with sudden exposure to low night temperatures in the fall. Improving the stress resilience of field-transplanted blackberry plants by recruiting plant endogenous protective metabolic responses has significant merit. Therefore, the aim of this study was to improve stress resilience of newly transplanted ‘Chester Thornless’ blackberry in the field during fall transition through stimulation of phenolic antioxidant and proline-linked metabolic responses by using bioprocessed chitosan oligosaccharide (COS) as an elicitor treatment. Fourteen-week-old blackberry plugs were transplanted in the field in late July and COS was sprayed weekly in the run-off for a 6-wk period after transplanting. Total soluble phenolic content, total antioxidant activity, total proline content, proline dehydrogenase, and succinate dehydrogenase enzyme activity of blackberry shoots were evaluated weekly during and 1 wk after COS application. Improvement in total soluble phenolic content and antioxidant activity based on 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) free radical scavenging assay was observed in field-transplanted blackberry at 6 and 7 wk with COS elicitation treatment.