Thobile Nxumalo (Variety Evaluation Scientist)
SASRI recommends the following best management practices for harvesting flowered cane:
- Flowering fields should be harvested before the end of September if the number of flowering stalks is more than 20% per field.
- Topping height of flowering cane is important, especially where pithing is severe. In such cases, a lower topping height is advisable.
- Avoid carrying flowering fields over, especially if the number of flowering stalks exceeds 20%. If flowering sugarcane is not harvested promptly, it becomes vulnerable to eldana and may also develop sour rot.
- Flowering stops vegetative growth, and yield will not increase any further. Be careful not to over-estimate the stalk yield of flowered cane.
- Avoid applying chemical ripeners excessively on heavily flowering crops (with over 20% flowering stalks per field) as this could increase the stress levels of the crops.
Varieties differ greatly when it comes to flowering: some flower more profusely than others because the propensity of a variety to flower is genetically determined. Also, due to the difference in genetic makeup of the different varieties, some will show greater cane quality losses in response to flowering than others.
This article presents observed cane quality losses from a variety evaluation (VE) trial in Darnall, North coast of KwaZulu-Natal, planted in September 2023 on a sandy soil site with 11% clay. The objective of the trial is to test the performance of twenty varieties under low soil potential conditions over different harvest cycles. Varieties tested in the trial, and the flower counts recorded at a crop of 10 months are presented in Figure 1. The trial was then harvested at 20 months in May 2025.
Flowering assessment was done at 10 months (July 2024) on two rows per plot for all varieties tested in the trial. Based on the flowering assessment, coastal varieties N77 and N76 showed higher flower counts compared to all varieties (Figure 1). Other varieties showed, flower counts of below 50 flowers in the two rows assessed for 2024 season.
Figure 1: Flowering counts of different varieties from the Darnall trial.
At 12 months (September 2024), the PurEst® App was used to estimate cane quality (RV%). All varieties were compared against N12 and N58, the popular varieties in the North Coast area. Variety N61 achieved the highest cane quality at 12 months, with the lowest cane quality being recorded for varieties N69 and N76 (Figure 2).
Figure 2: Estimated RV% of different varieties from the Darnall trial.
Cane quality at 12 and 20 months was compared to determine the cane quality losses when the cane was harvested 7 months later than what SASRI recommends for flowered cane (Figure 3). At harvest, coastal varieties N55 and N64 achieved the highest cane quality. Variety N55 recorded the third most flowered variety in the trial – even though the flower counts were below 50 – but still achieved slightly higher cane quality at harvest, 8 months later than the recommended harvest time for flowered cane
Figure 3: Cane quality RV% difference for 12 vs 20 months age in from the Darnall trial.
Variety N61, recorded the highest cane quality at 12 months, although there were no flowers recorded at 10 months, at 20 months there was a significant cane quality decrease of 4.03 RV%. Coastal varieties N76 and N77 which are known to flower profusely, showed cane quality decreases of 3.02 and 2.6 RV% respectively. Popular variety N58, showed a decrease of 0.8RV% (Table 1). Midlands variety N75 showed the highest decrease in cane quality of 4.66RV%, which might indicate strong sensitivity to cane quality losses associated with flowering.
Table 1: Shows the RV% achieved and differences at 12- and 20-months harvest age
| Variety | RV% at harvest age of | Difference in RV% | |
| 20-month | 12-month | ||
| N12 | 9,29 | 12,50 | -2,59 |
| N51 | 10,34 | 12,20 | -3,38 |
| N54 | 10,11 | 12,70 | -4,03 |
| N55 | 13,43 | 13,00 | -2,77 |
| N58 | 11,58 | 12,40 | -1,88 |
| N59 | 9,82 | 13,20 | -0,51 |
| N61 | 9,47 | 13,50 | -2,43 |
| N62 | 8,57 | 11,30 | -0,20 |
| N63 | 9,23 | 12,00 | -1,86 |
| N64 | 12,96 | 12,80 | 0,43 |
| N66 | 10,72 | 12,60 | -2,73 |
| N67 | 11,79 | 12,30 | 0,16 |
| N69 | 9,87 | 11,10 | -3,21 |
| N72 | 9,07 | 11,50 | -0,82 |
| N74 | 11,80 | 12,00 | -1,23 |
| N75 | 7,84 | 12,50 | -4,66 |
| N76 | 7,98 | 11,00 | -3,02 |
| N77 | 8,80 | 11,40 | -2,60 |
| N78 | 11,22 | 13,10 | -1,88 |
| N79 | 11,23 | 12,60 | -1,37 |
These results give some idea to the extent of cane quality losses associated with flowering, although there may be other factors contributing to cane quality losses observed in the trial. Some varieties like N55 and N64 appear to be less sensitive to cane quality losses even when harvesting was delayed after a flowering event. Therefore, planting shy-flowering varieties in fields to be harvested in September is highly recommended.
Flowering is initiated when the minimum night temperature in March is 18°C or higher with adequate soil moisture availability and a day length of 12.5 hours or shorter. It is a natural physiological process that is undesirable because it can lead to cane yield and quality losses, and thus reduced RV yield. The losses occur because of physiological and biochemical changes that takes place in the cane when the plant shifts from vegetative growth to reproductive development. Initially, the changes that occur because of flowering are not all bad, until flowered cane is left unattended by the end of September.
For more information, see Information Sheet 4.3: Flowering and pithing in sugarcane.