Livestock producers in the southeastern United States utilize native warm-season grasses (NWSG), however, the best management practice to not harvest during late-summer and fall results in large quantities of low quality forage. Gibberellin inhibitors can alter plant regrowth and forage value. This study assessed the impact of trinexapac-ethyl [TE; ethyl 4-(cyclopropyl-hydroxymethylene)-3,5-dioxo-cyclohexane-1-carboxylate] on fall NWSG forage. Application of TE occurred in late July at four levels (0, 0.3, 0.6, and 1.2 kg a.i. ha-1) to switchgrass (SG; Panicum virgatum L.) and a mixed sward (BBIG) of big bluestem (Andropogon gerardii Vitman) and indiangrass (Sorghastrum nutans L.) during 2016 and 2017. Forage mass (FM) and nutritive value [crude protein (CP), neutral detergent fiber (NDF), in vitro true dry matter digestibility (IVTDMD)] were evaluated monthly. Application reduced fall FM (SG: 37%; BBIG: 42%). Switchgrass nutritive value did respond to TE application. Application of TE reduced BBIG NDF overall, but strong annual variation occurred due to a drought (2016). Analyzed separately, 2017 treated BBIG samples (1.2 kg a.i. ha-1) exhibited altered FM (−57%), CP (up to 54%), NDF (−9.2%), and IVTDMD (11%). Further analysis provided tentative evidence that TE improved leaf nutritive value and increased leaf proportion, although overall leaf yield was not improved. Overall, TE improved BBIG nutritive value but at a substantial FM loss. Since poor nutritive content forage has negligible value regardless of quantity, growth regulators could improve outcomes of fall NWSG management by adding value to an unutilized resource.