A. Propagation and Nursery Management
Litchi seedlings are typically propagated sexually for breeding studies and as rootstocks for grafting. Fresh litchi seeds remain viable for about a month post-harvest with around 45% moisture content, but this viability rapidly diminishes within 4–5 days once removed from the fruit, particularly when moisture content falls below 27%. To transport seeds, they are often packed in moist sphagnum moss, although germination can occur within the packing material itself, usually within a week. For better germination and seedling development, larger seeds and mycorrhizal soil are recommended. Germination usually occurs within 4–10 days in various substrates like soil, sand, vermiculite, or peat, provided there is enough moisture and aeration. However, seedlings are not typically used for new plantings due to their extended juvenile phase of up to 10 years.
Some areas on the tree branched are wrapped up in aluminium foil. Wrapped inside the foil is sphagnum moss which provides an environment for roots to develop. Each of the parts wrapped will become individual trees later on
Asexual propagation, particularly air-layering, has been the traditional method for litchi. This involves wrapping moist peat or sphagnum moss around a girdled branch area, secured with plastic sheets. Root formation usually takes place within 8–10 weeks, and the success rate of this method is nearly 100%. Growth regulators are generally not necessary for enhancing rooting, although some practitioners use preparations like lanolin paste with IBA or IAA.
Grafting in litchi, though variable and often challenging due to stock-scion incompatibility and other factors, is still practised. It requires precise timing and good management post-grafting.
B. Field Preparation
Before planting, deep ripping may be necessary for compacted soils. Liming to adjust the pH to 5.0–5.5 and incorporating manure are common pre-planting practices. Litchi trees can tolerate poor drainage but perform poorly in standing water, hence adequate surface drainage is essential. Nematode issues are addressed through soil fumigation. In well-drained alluvial soils, longans exhibit optimal growth.
C. Transplanting and Plant Spacing
Transplanting sun-hardened trees, typically 6–12 months old, is viable at any time of the year, provided there is sufficient moisture and no frost risk. Mulching post-fertilisation benefits young trees. Seedlings start fruit production in 6–10 years, while asexually propagated trees take about 3–5 years. Plant spacing varies from 5–12 meters depending on the cultivar size, with regular pruning required to prevent overcrowding.
D. Irrigation
Regular irrigation is crucial for young litchi trees, especially during dry periods. For mature trees, moisture control becomes important to balance vegetative growth and flowering. In regions with dry summers, irrigation followed by limb girdling in late summer is practised to accumulate carbohydrates in the trees during autumn months, a practice necessary in areas without natural winter dormancy. Litchi trees require a period of dormancy to build up enough reserves for their flowering season. Depending on the region, water restriction from March to May can be employed to encourage this resting phase. However, this technique’s effectiveness can vary based on the local climate, such as unexpected late rains in March and April. When implementing this water stress strategy, it is crucial to ensure that the trees are not completely deprived of moisture.
E. Pruning
Pruning in litchi aims to remove low-hanging branches to facilitate cultivation and prevent branches from bending to the ground when laden with fruit. In bearing trees, even branches at 1.5 meters can require pruning. A pruning system is also practised in Taiwan to maintain a smaller tree size and encourage regular flowering and ease of management and harvesting.
Vegetative growth occurring in the autumn or early winter can hinder or even stop the flowering of litchi trees. To manage this, the application of the plant growth regulator ethephon is recommended. Ethephon works by eliminating the young leaf flush, thus facilitating flower development when temperatures sufficiently decrease.
Girdling of litchi trees, although not a common practice, can be carried out around mid-March after the growth of the post-harvest vegetative flush has stabilised. This process helps to restrict vegetative growth in the period leading up to flowering. However, this method might not always effectively prevent new leaf flushes, in which case, it may be necessary to apply ethephon as a follow-up treatment.
F. Fertilisation
Fertilisation practices vary based on climate, soil type, and availability of different fertilisers. A light application is recommended immediately after field transplanting due to litchi roots’ sensitivity to fertiliser burns. The general recommendation for older trees includes applications of urea, superphosphate, and potassium sulfate, with adjustments in amounts based on tree age and bearing status.
Critical nutrient periods include the time before flowering and fruit set, several weeks after fruit set, and post-harvest. The main fertilisation is done immediately after harvest in the summer, followed by irrigation and annual limb girdling. For bearing trees, a rule of thumb is 0.90 kg of complete fertiliser per 2.54 cm of trunk diameter upon harvest completion.
G. Erratic Bearing
Litchi trees, which can produce up to 45 kg of fruit at 7-8 years of age, show considerable variation in annual yields. This erratic bearing can be attributed to fluctuating weather conditions, cultivar-specific climate requirements, and management practices. To achieve more consistent yields, an integrated approach that includes cultivar selection, pruning, and tree management is necessary. Both litchi and longan require stimulation for leaf growth post-harvest, followed by a period of rest, then floral induction and development, influenced by factors such as fertilisation, rainfall, and irrigation. Proper management of these phases is key to optimising fruit bearing.
Pest Management
Effective pest and disease management is crucial for the successful cultivation of litchis in South Africa. Given the economic significance of litchi production in the region, growers must adopt comprehensive strategies to mitigate the impact of pests and diseases on their crops. Integrated Pest Management (IPM) is a sustainable approach that combines various management practices to control pest and disease problems effectively. IPM focuses on long-term prevention and control through a combination of techniques such as biological control, habitat manipulation, modification of cultural practices, and the use of resistant varieties. Chemical pesticides are used as a last resort and applied in a manner that minimises risks to human health, beneficial organisms, and the environment.
A. Diseases
In the cultivation of litchis, several diseases pose significant threats to the health and productivity of the trees. The Persea mite is one such threat, known for attacking litchi leaves and impairing their ability to photosynthesise effectively. Managing this pest involves regular monitoring, the introduction of natural predators, and, in severe infestations, the use of miticides. Early detection and prompt action are crucial to prevent widespread damage.
Another major concern is Anthracnose, a fungal disease caused by Colletotrichum gloeosporioides. This disease affects the leaves, flowers, and fruits of the litchi plant, resulting in dark lesions and a consequent reduction in yield. To combat Anthracnose, strategies like the application of fungicides and improved cultural practices are employed. These practices include pruning to enhance air circulation within the canopy and reduce humidity, thereby limiting the spread of the fungus.
Root Rot, often linked to poor drainage and caused by fungi such as Phytophthora spp., can also be a serious issue. It leads to the decay of the tree’s root system, significantly impacting the tree’s health. Preventative measures are key in managing Root Rot, which involves choosing well-drained planting sites and using resistant rootstocks. In areas prone to this disease, fungicides are applied as a preventive measure to protect the trees from infection.
B. Insects and Other Pests
Litchi Stink Bugs, known for feeding on the sap of litchi trees, can cause considerable damage and weaken the trees. Effective management of these pests involves the use of appropriate insecticides and maintaining orchard hygiene, such as removing weeds and debris that can harbour these bugs. Regular monitoring and timely intervention are crucial for controlling their population.
Fruit flies pose a significant threat to the quality of litchi fruits as they lay eggs inside the developing fruits, leading to spoilage. To manage this issue, traps and baits are used to capture adult flies, and maintaining orchard cleanliness through the removal of fallen and infected fruits is vital to break the life cycle of the flies. The use of bait must be applied correctly and regularly to ensure good results – 5 g trichlorfon 95% wsp + 25 ml protein hydrolysate (or 800 g sugar) + 10 litres of water. Apply to each tree by using a knapsack sprayer. Apply twice a week.
The litchi moth is particularly notorious for its similar life cycle to the macadamia nut borer and its ability to infest a range of host plants including macadamia, Bauhinia, Caesalpinia, and Acacia species. Understanding its life cycle is essential for implementing targeted control measures. No chemical control has been useful yet.
Litchi moth
Furthermore, the Natal fruit fly and the false codling moth are serious pests that infest litchi fruits, causing spoilage and significant crop losses. Strategies to manage these pests involve the use of traps, baits, and sometimes insecticides, coupled with rigorous orchard hygiene practices.
Bark borers and nematodes present additional challenges. Bark Borers can damage the bark and wood of litchi trees, thereby reducing tree vigour and productivity. Nematodes, particularly root-knot nematodes, impact the root system, hindering the tree’s ability to absorb water and nutrients. Managing these pests often involves cultural practices and the use of nematicides or other suitable control measures.
In addition to these insect pests, litchi orchards in South Africa face challenges from local wildlife such as vervet monkeys, bats, and birds, including mousebirds and bulbuls. These animals cause direct damage to the fruits, leading to crop losses and spoilage. To mitigate this, non-lethal deterrents such as netting, scare devices, or other wildlife management strategies are employed to minimise damage while respecting the local ecosystem.
Harvesting
In South Africa, the harvesting of litchis is meticulously timed to ensure the highest quality and flavour of the fruit. Litchis, being non-climacteric, do not ripen further after being picked and do not respond to ethylene treatment. They are ready for harvest when they attain a full red colour; harvesting them prematurely results in acidic fruits that do not improve in flavour post-harvest.
The common harvesting practice involves detaching the entire panicle with the fruit cluster, a method that not only gathers the fruits but also stimulates the growth of new flowering terminals for the subsequent season. In smaller orchards, traditional tools like bamboo or aluminium tree-pruning poles and tall ladders are used, whereas larger orchards often employ mechanical ‘cherry pickers’ to enhance efficiency and ease of harvesting.
A trend in South African litchi cultivation is to maintain trees at a height of less than 3 meters. This manageable height facilitates ground-level harvesting and overall orchard management, making the process quicker and more efficient.
For harvesting, especially of larger trees, ladders or automated picking trailers are utilised. Picking is usually done during the cooler parts of the day, preferably in the morning, to minimise desiccation and browning of the fruit skin. In the orchard and during transport, harvested fruits are kept cool and often covered with leaves or wet hessian to maintain freshness.
Harvesting times and conditions are also critical. To avoid impacting the fruit’s colour and longevity, it is generally advised to avoid harvesting in the afternoon or on rainy days. Once harvested, litchis are packed in straw baskets or cartons, each weighing around 15-20 kg, with green leaves included to help preserve moisture and the fruit’s colour. To prevent rapid drying, it is crucial to keep the harvested fruits shaded from direct sunlight.
The maturity of litchis for harvest is determined by specific cultivar characteristics such as fruit colour, shape, and flavour, along with a total soluble solids (TSS) to titratable acid (TA) ratio of 25:1. Due to uneven fruit ripening within a cluster or across a tree, selective picking is employed at the season’s start. The use of a fruit diameter measure, or picking ring, ensures adequate fruit size. As the season progresses and ripening becomes more uniform, entire fruit clusters are harvested, leaving about 3 mm of the stalk on each fruit to prevent skin splitting.
Postharvest Handling
At the packing shed, fruits are pre-sorted to eliminate any damaged or stung ones. Healthy fruits then undergo sulfur dioxide fumigation to prevent skin browning and reduce fungal infections, thereby extending shelf life. Post-fumigation, fruits are sorted by size, adhering to a minimum diameter of 30 mm for export and 28 mm for the local market. Litchis are packaged in either 2 kg cartons or smaller plastic punnets, depending on the market. For long-term storage, cartons with a slow-releasing sulfur dioxide sheet are used.
The shelf life of untreated litchis at room temperature is just a few days, but when refrigerated at 4°C in sealed punnets, they can last up to two weeks. Sulfur fumigation extends the shelf life even further, up to five weeks at 1°C.
Maintaining product quality in litchi sorting involves the meticulous removal of damaged and inferior fruits. This stage requires careful attention and adequate lighting, whether sorting is done on a table or along a conveyor with rollers. It is crucial to inspect every fruit thoroughly to ensure no damaged ones are included in the packaging. Damaged fruit, particularly those with compromised arils, are prone to rapid rotting, which can spread to other fruits in the package. Therefore, fruits with pulled stems, splits, cracks, or signs of insect damage must be discarded during sorting.
Fruits damaged by piercing moths the night before harvesting may not show immediate signs of damage but typically exhibit weeping and tissue darkening within 24 hours. To detect such damage, some growers store the fruits overnight in high-humidity cold stores, allowing time for any signs of damage to become evident. In situations where cold storage is not available or a faster process is needed, squeezing the fruit can often reveal recently stung fruit through the leakage of aril juice. Additionally, immature fruits and those showing any rot signs are removed during sorting.
Some markets are particularly sensitive to cosmetic flaws such as scale infestation, small size, severe pepper spot (anthracnose) infection, or superficial browning. Fruits with these defects are typically downgraded; they are not sent to central markets but may be processed or sold at roadside stalls instead.
Grading
Litchis are classified into different grades based on quality, appearance, and condition. Each grade has specific requirements and tolerances.
- Extra Class Grade: Litchis in this category must be of superior quality, displaying the shape, development, and colouring typical of their variety or varietal type. They should be essentially free from defects, except for very minor superficial ones that do not impact the overall appearance, quality, longevity, or presentation in the package. Up to 5% by number or weight of the litchis may not fully meet these requirements but should conform to those of Class I grade or, in exceptional cases, fall within its tolerances.
- Class I Grade: Litchis of this grade should be of good quality and characteristic of their variety or commercial type. They are allowed to have slight defects in shape, colouring, and minor skin blemishes, as long as these do not cover more than a total area of 0.25 cm2. and do not affect the general appearance, quality, keeping quality, or presentation. Up to 10% by number or weight may not meet the full requirements of this grade but should meet those of Class II grade or, exceptionally, fall within its tolerances.
- Class II Grade: This grade encompasses litchis that do not qualify for the higher grades but meet the minimum specified requirements in general characteristics. Defects in shape, colouring, and skin blemishes are allowed, provided they do not exceed a total area of 0.5 cm2. and the litchis still maintain their essential characteristics in terms of quality, keeping quality, and presentation. Up to 10% by number or weight may not fully meet the grade requirements but should meet the minimum requirements.