Cultivar management

Recovery from frost is also important in lower lying valley bottoms. van Heerden et al. (2009) tested two Louisiana cultivars (LCP 85-384 and HOCP 96-540) against two South African cultivars (N21 and N36). LCP 85-384 and N36 were better able to cope with frost than N21 and produced 30 % more sucrose.

It is often only after a cultivar has been commercially grown for a number of years that one has a real understanding of potential under the wide set of conditions that are a reality in commercial production.

1.7.3 Main components of yield

When selecting cultivars for yield it is important to appreciate the impact of the three main components of yield (population, stalk mass and cane quality) on management and performance.

Stalk population and mean stalk mass multiplied together equals cane yield. In general, high populations have lower stalk mass and vice versa. Cane quality is determined in the mill laboratory, mainly as pol % cane, brix % cane and fiber % cane and, when multiplied by cane yield, provides the mass of pol, brix and fiber produced. Each component interacts on GMP. High populations would tend to protect the soil, add more trash and result in more cutting strokes at harvest, and have more fiber and tend not to lodge as much. In contrast, heavy stalks tend to produce more sugar and less fiber, and may be inclined to lodge more easily, but have lower transport costs per tonne sugar delivered to the mill.

The growing demand for power has increased the importance of cogeneration to supply the local grid. This has increased the value of bagasse (fiber) and will in the future impact on cultivar choice.

1.7.4 Harvesting and transport

Cultivars with hairy stalks meet with cutter resistance, especially in seedcane and green cane. When cane is burnt before harvest, hairiness is not as significant. Brittle cane and lodged cane does not form good tight bundles and can produce low payloads and increased losses in the field. Uniformity in height helps with both manual topping and mechanical harvesting.

When there is a choice, mechanical harvesting should be restricted to ratoon crops and to when the weather is dry and limits compaction. It is important to ensure that the cane is planted on the correct gradient for the soil type and that contour planting is used on slopes. There is a move to precision planting and the use of fixed beds. For cultivars and machinery to perform well, it is essential that beds should be uniform with good surface runoff and good infield drainage.

Bella et al (2009) found that the disadvantages of an early start to the milling season far outweighed a late finish and that there is a cultivar x time of harvest interaction that needs to be exploited more fully.

Transport is a major cost particularly when long distances are involved. The further from the mill the more important it is to select cultivars with good bundle weights and high sugar, total fermentables (ethanol) and fiber for cogeneration (see Chapters 12 and 13).

1.7.5 Milling quality characteristics (see also Section 2).

The mill balance and efficiency in milling also impacts on cultivar. Some cultivars (e.g. N25) are not suited to the diffuser process as they are not suited to cane preparation processes and this impacts on performance. Cultivars should be tested for milling before final large scale commercial release.

The mill balance determines what proportion of sugar coming in at the front end is available after processing at the back end. Milling efficiency is used in many of the calculations to determine payment for sugar (e.g. RV % in South Africa, CCS in Australia and ERC % cane in Zimbabwe, whilst some industries still pay on the basis of pol % cane or cane yield). The mill balance for a cultivar is important as it often impacts on grower payout and on its economic performance.

1.7.6 Plant breeding and selection

There is a wide exchange of material between the major breeding centers in an effort to increase the chance of crossing to produce superior cultivars. Breeding, selection and cultivar release is a long term process as can be seen from an example given in Table 1.3.

Table 1.3. Summary of 10 years of selection, bulking-up, testing and release in Zimbabwe (1976 to 1986).

Stage of program Total number of cultivars tested

Percentage selected at each stage

Single stools 516 457 5.91

Single lines 30 507 8.99

Cultivar observation trials 2 742 7.11

Advanced cultivar trials 195 26.15

Pre-release cultivar trials 51 15.69

Pre-release bulking 8 37.50

Limited release 3 −

General release − −

1.7.7 Field and planting hygiene

A fallow period of three months without any plant debris including stools is required for RSD control.

A break crop with any non-gramminaceous plant (e.g. soybean and other beans) also improves soil fertility and promotes sustainable production. In addition there is a need to prevent plant-to-plant spread of disease, particularly RSD by continuously disinfecting cane knifes particularly in the nursery stage. Mechanical harvesters should be chemically treated to prevent cutter blades spreading RSD between fields. Regular inspection and roguing form part of the hygiene practices recommended, particularly for nurseries, but also in the commercial crop where warranted.

The time of planting impacts on pest and disease pressure. This is most intense in the wet season.

Planting late predisposes plants to increased pest and disease attacks (e.g. from Black Maize Beetles and mosaic disease). Resistant cultivars are particularly valuable for late-planted cane.

Ensuring that the stalks are cut cleanly at ground level with sharp cane knives or cutter blades, with the use of recommended disinfectants, applied correctly, facilitates ratooning and helps keep insect pests and diseases in check. Burning, although not recommended, can be used to help control a serious outbreak of a pest or disease that lives on plant residues.

1.7.8 Seedcane management important requirements

The success of any cultivar commercially is as dependent on the cultivar as it is on the management of the seedcane, which requires clean land and regular inspection, and often roguing and HWT. A

cultivar can only perform to its potential if the seedcane is well grown and is pest and disease free.

This is often the greatest limitation on new projects and provides potential for the use of plantlets from tissue culture or speedlings from single setts.

The production of seedcane has to be linked into the bulking-up and commercial planting program, and cognizance must be taken of the time of planting − which must relate to milling in the early, mid or late season. Each part of the milling season has cultivars suited to it. For example early season cultivars are early maturing; mid-season cultivars are more versatile and late season low flowering cultivars have greater pest and disease resistance.

Seedcane schemes help to bulk up new cultivars for release at the correct time for planting out.

Schemes can be organized at different levels, from country (Swaziland and Zimbabwe) to regions (e.g. Felixton in South Africa (Fortmann et al. 2006)).

Bulking-up nurseries

Cultivars are often bulked up in two stages. The first stage follows HWT to control RSD, and germination may be reduced as a result of this treatment. The next stage is to further bulk-up in a nursery without HWT and then use this material for commercial planting, and some to HWT to establish another first stage nursery. It is normal to grow cane for about 8 to 10 months before using it as seedcane but this can vary depending on the cultivar and its vigor. Seedcane is not dried off and is preferably irrigated and not burnt. Inspection and roguing for trueness to type, for abnormal growth and for pests and diseases is essential for the production of good seedcane.

Chemical protection of setts

Setts of cultivars susceptible to smut are cold water dipped for at least three minutes in a suitable fungicide.

An approved and recommended insecticide should be sprayed on setts in areas susceptible to insect pests, such as termites, cane grubs, stalk borers and false wireworms. Some insecticides and

nematicides need soil incorporation and may be banded and covered.

It is important to use only those chemicals that are approved and which comply with health, safety and environment considerations and regulations.

Certification of nurseries and commercial fields

Diseases and pests must be below set thresholds in nurseries and commercial fields where susceptible cultivars are under pest or disease pressure. Each industry should determine suitable thresholds and control cultivar use and distribution as well as time of planting. This helps protect cultivars in use, particularly in areas vulnerable to pests (e.g. eldana) and diseases (e.g. smut in hotter areas and mosaic in cooler areas).

It is common to use lower thresholds for nurseries than for commercial crops. Zimbabwe and Swaziland managed to continue growing NCo376 for many years despite the threat from smut and mosaic because of rigorous roguing, inspection and certification of nurseries, as well as plough out, by order, of commercial fields with higher than acceptable smut levels. The high cost of roguing and the level of management required for effective roguing have resulted in rapid adoption of resistant cultivars.

Industries often set up independent pest and disease teams to monitor the situation and an industry committee to carry out the withdrawal of nurseries and implement field plough-out orders.

Breeding centers

All major producing countries have breeding stations that are central to their research programs.

There is often linkage to other institutions with sophisticated molecular and analytical equipment necessary for advancing the industry. There is good collaboration between the major producers, and breeding material is regularly exchanged to mutual benefit. It is important for smaller industries to realize this and to ensure that they obtain material from these institutions for comparison with their own local selections.

Mitigating risk

The selection of cultivar should be based on optimizing production with minimal chemical or other inputs and should be able to withstand any perceived risks from pests or diseases.

The payment system should ensure that better cultivars are rewarded for quality. This can even be done on the basis of cane payment by giving these cultivars a higher cane price. There needs to be a good tracking system on cultivar use.

A cultivar can only perform to the level of management it is given and the production system needs to be sustainable. Zero till and controlled traffic systems are under investigation and the inclusion of a fallow or break crop is becoming more common.

The main threat is climate change and lack of adequate water. Therefore drought tolerant cultivars are particularly necessary under monoculture where soil conditions are deteriorating, particularly in the more marginal areas.

The best start one can have is to use the best cultivars, free of pests and diseases, and to establish them under the best conditions.

Tissue culture offers the advantage of providing a sufficient quantity of disease free material to new green fields projects. However, the project must have the levels of expertise to manage the material properly. Plantlets should be established in the field under favorable climatic conditions (not too hot or cold) and well before the rains. This will help limit the threat from the main sugarcane pests and diseases but control of other factors may become important (e.g. animal grazing).

Surface and subsurface drainage are essential under many of the more marginal conditions where cane is being planted. An excellent topographical and soil survey is required as a basis for a sound conservation layout.

Monitoring and control (e.g. leaf and soil analyses and irrigation scheduling) and good record keeping can all help improve cultivar selection, performance and management.

Doing the simple things properly and on time will determines the potential of a cultivar.

At industry level there is a need to continuously evaluate cultivar performance and determine areas with shortcomings. A spread in the mix of cultivars is recommended, but this must take cognizance of the opportunity cost of not using the best cultivars.

Risks must be evaluated and strategies worked out well in advance. Having a surplus of good material to plant is recommended for all sectors of the industry.

Smallholders are often at greatest risk and the choice of resistant cultivars is particularly important for them. They also need to have a financial plan to allow replanting and to change cultivar in time.