Recent shifts in sugarcane variety adoption in the KwaZulu-Natal Midlands have created complexity in managing mixed crop cycles. Older varieties like N12 have traditionally followed a 24-month cutting cycle, but many of the new varieties (released since 2007, following N48), characterised by enhanced growth characteristics and high yield potential, are prone to lodging under favourable growing conditions, necessitating earlier harvesting (18 months or less). This shift can disrupt field operations, cane quality management, replanting strategies and cane supply consistency, especially where mixed variety types are grown. Growers are increasingly asking: At what age should I harvest the new varieties to get the best return?

To help answer that question, SASRI recently concluded a research project in March 2025, which developed a decision support approach for optimising variety management in the Midlands, focusing on variety selection, harvest timing and yield. The study analysed five years (2019-2023) of commercial harvest data from 17 Midlands farms—nine in the South and eight in the North—spanning over 5000 fields, representing around 14% of the area under cane in each region.

The analysis focused on three broad variety groupings: old varieties, with relatively slow canopy development and low lodging susceptibility (“SLowLow” : N12), and two groups of newer varieties with fast canopy development, and average (“FastAvg” : N16, N31, N37, N39, N42, N45, N48, N50, N58, N59, N62, N66) or severe lodging risk (“FastSev” : N36, N52, N54, N55, N61). The data were further grouped by harvest age (in four-monthly intervals from 12 to 31 months) and harvest period (early, middle, or late season). For each region x variety group x harvest period combination, annualised RV yield (ATRV, t/ha/annum) was evaluated to determine the optimal harvest age range associated with peak ATRV.

Research Project Results

Results showed clear statistical differences in ATRV for most region x variety group x harvest period combinations and could be used to identify optimal harvest age ranges based on peak ATRV (Table 1). In many cases, new varieties performed best when harvested between 12 and 19 months, while the traditional 24-month cycle remained optimal only for N12 in the Midlands South. In only two cases was a statistically significant optimal harvest age not identified, e.g. for N12 early-season crops in the Midlands South, suggesting no clear advantage to harvesting earlier or later than the conventional 24-month cycle.

Table 1. Summary of optimal harvest ages (months) identified with statistical analysis of annualised RV yield (ATRV) from commercial production data in the Midlands regions, for crops harvested at different times of the season (early/middle/late) and for groups representing old (SlowLow) and new (FastAvg or FastSev) sugarcane varieties. NS = not significant.

Importantly, the study went a step further by combining these RV yield insights with an economic analysis. Using region-specific costings, including extraction and crop management costs, the study compared gross margins across harvest ages. In most cases, the optimal harvest age associated with peak RV yield also provided the highest economic return (Table 2). For example, FastSev varieties in the Midlands South showed peak ATRV and the highest gross margins when harvested at 12–15 months for mid and late season harvests, while N12 remained best harvested at around 20–23 months.

Table 2. Summary of optimal harvest ages (months) identified with economic analysis of gross margins in the Midlands regions, for crops harvested at different times of the season (early/middle/late) and for groups representing old (SlowLow) and new (FastAvg or FastSev) sugarcane varieties.

In the Midlands North, for FastSev varieties, the economic results showed that best returns in the early season are achieved at harvest ages of 16-19 months, while in the middle of the season crops can be aged to 20-23 months. However, in the late season, harvest age is a major factor with loss of return if a harvest age of 15 months is exceeded. This highlights how combining agronomic and economic data can lead to better on-farm decisions.

These results will be presented and discussed in more detail through regional grower newsletters and at upcoming grower days in 2025. While the findings are broadly relevant on a regional scale, growers are encouraged to approach harvest age optimisation on a case-by-case basis. Factors such as farm location, layout and topography, soil type and variety selection all play a role. Long-term whole-cycle economics—including long-term implications for ratooning, replanting, and logistics—should also be considered. In addition, this study could not account for the effects of soil type and ripener applications due to limited records, but both are known to influence crop performance and should be factored into on-farm decisions.

We extend our sincere thanks to the growers who contributed commercial data to this research. Their willingness to share accurate and detailed records made this analysis possible. We encourage all growers to keep detailed farm-level records to enable similar region-specific insights in future.

*Research Team: Natalie Hoffman (Crop Scientist), David Clark (Programme Manager), Aresti Paraskevopoulos (Scientific Programmer), Riekert van Heerden (Research Manager), David Wilkinson (Acting Extension Manager), Paul Botha (Extension Specialist- Midlands South) and Muhammad Kadwa (SA Canegrowers’ Industry Affairs Manager).