In both regions, the optimal harvest age identified here was younger than that reported in previous studies that involved single cultivars.McIntyre and Nuss (1998) showed that sugar yields of N12 compared with NCo376 and N16 were superior at harvest ages greater than 22 months for the inland region, and at 18 months in the coastal region.Through simulations of cultivar NCo376, Inman-Bamber (1991)found an economic optimal harvest age of approximately 17 months for the coastal region. Inman-Bamber (1995) also illustrated through simulation the superior sucrose yields of the 18 month vs. the 12 month harvest age in different locations. It must be noted that the effects of harvest age and crop start date are intricately linked, and to unravel these dynamics these two factors would need to be considered together. Past studies (Moberly, 1971; Lonsdale and Gosnell, 1975; Rostron, 1972)involving these interactions generally showed that the optimal harvest age decreased as crop start date proceeded from the beginning to the end of the milling season in South Africa. In this study, confounded data from different crop start dates, soil types, yield potential conditions, and ratoon numbers were pooled in an attempt to identify broad practical recommendations given the current suite of culti-vars available. These trends are therefore considered to be more realistic (for broad industrial use) than the site and cultivar specific studies in the past. To understand the current variability in cultivar × harvest age interactions, selected cultivar responses to HA were investigated further, as described below.