ABSTRACTThe agronomic value of Syn 1 tall fescue, a synthetic variety derived from North African parent material, was determined in three experiments. Herbage yield, sward purity and digestibility were measured under cutting treatments for incremental sward growth during autumn/winter, and for sward regrowths during autumn/winter, spring and a complete season. Similar data were obtained for sward regrowths during autumn/winter and spring under defoliation by grazing. Syn 1 was compared with several of the north‐temperate region tall fescues, e.g. S170, Rozelle and Manade, also with S143 cocksfootSyn 1 showed yield superiority in autumn/early winter when there were comparable populations of tall fescue. Under cutting management, Syn 1 swards thinned out rapidly because of lack of winter‐hardiness and yields were depressed in the second season; the effects were worst under the winter foggage‐type management. Under grazing, with probably less severe defoliation, Syn 1 swards maintained yields for an additional season, but thereafter failed to persist Syn 1 swards had low spring‐ and annual‐yields.The yield advantage of Syn 1 in autumn/early winter was not sufficient to be of great agricultural value and with its shortcomings in winter‐hardiness and annual yield, it was considered unsuitable for West of Scotiand conditions. The main value of plant material such as Syn 1 may lie in ccmferring autumn/winter growth potential to winter‐hardy north‐temperate tall fescues in a bre