The effects of delayed winter spur-pruning on yield, yield components and fruit composition of Merlot vines was evaluated within a commercial vineyard in Marlborough, New Zealand. Vines were spur-pruned, trained using vertical shoot positioning, trickle irrigated and grafted to Kober 5BB rootstock. Delaying pruning from July (usual winter pruning time in New Zealand) until up to October (when apical shoots on canes were 5 cm long) resulted in yield increases of up to 93%, 63%, and 82% over the three seasons of experimentation. These yield increases reflected higher average berry weight and in turn bunch weights. The increase in average berry weight was associated with a change in the relative abundance of different berry types. Later pruning increased the proportion of large seeded berries while the proportion of smaller seedless berries and live green ovaries (shot berries) decreased. The delayed pruning may have enhanced fertilisation of flowers and development of seeds by postponing flowering to a time when climatic conditions are more favourable; measurements of shoot lengths support this proposal. By delaying winter pruning until after budburst the development of basal nodes was inhibited, so that budburst on the resulting spurs was also delayed.