Pruning and Training of Vanilla Plants
The pruning and training of vanilla vines is one of the main agronomic measures required to regulate vegetative and reproductive growth, to reduce the occurrence of vanilla disease and to provide propagation cuttings and so on. Depending on different pruning purposes, the main parts to be pruned may include the infected portion of a plant, or weak and flowered vines.
The disease-infected leaves, stems, and fruits should be removed as early as possible so as to check the spread of the disease. Aging vines need pruning periodically to stimulate the induction of offshoots and the promotion of vegetative growth. The tips of slim vines and juvenile plants reaching a height of over 50 cm should be nipped off. With this method, more than one offshoot will come out and the branches will become stronger. However, more water sprouts and branches should be removed or inhibited by pruning, especially during the flowering and fruit development period. Branches that have flowered and borne fruit and have no living axillary buds can be cut off, since they will not produce any flowers. A specific pruning of hanging branches on adult plants is generally carried out 3–4 months before the flowering season—around November to December in China—to encourage the production of inflorescences in the axils of the leaves on the hanging branches. When the desired number of fruits per inflorescence has been reached after pollination, the remaining buds and the tip of inflorescences should be removed.
As essential as pruning measures are, vanilla vine training is also helpful in facilitating the even distribution of the vanilla vine on the climbing trellis in order to maintain a sustainable biomass and yield. Generally, the vines of the initial planted seedlings attached to the column of the supporting trellis or the erected bamboo sticks beside it always grow upward. When the vine or branch climbs up and reaches the top of the trellis, it should be brought back to the ground, and the portion of the vine with 4–5 nodes should be covered with surface soil or mulch, which will induce the vine under ground to take root and thereby support the whole plant in order for it to grow well. Thus, the vines are looped up and down, and evenly distributed on the supporting trellis, but do not accumulate on the top half of the trellis. Gradually, vanilla plants develop into a row along the planting belt, reaching as high as the trellis. Vanilla vines can be trained along the whole trellis within the same row.
Weeding
Weeds in vanilla plantations do little harm to vanilla plants. The aim of weeding is simply to prevent competition for nutrients with vanilla plants. There are many different species of weeds in newly established vanilla plantations that grow in abundance, especially during the rainy season. Weeds should be cleared before blossoming and fruit bearing, and can be used as mulch and organic fertilizer after fermentation. With manual weeding, the quantity and species of weeds will gradually diminish to a lower level until the third year.
Other Maintenance
In Xishuangbanna and some regions of Hainan Province, the annual alternation of dry and rainy seasons leads to soil compaction, poor root growth, and the incidence of diseases. Depending on the soil water content and moisture, in combination with mulching, adequate irrigation during the dry season is essential for vanilla plants to grow well. Lack of irrigation would lead to the death of aerial roots, and even the death of the plants suffering from water deficits. It is recommended to irrigate plants by frequent and low-volume sprinkling during extended dry periods, and to avoid waterlogging, especially in the rainy season.
Typhoons in the Hainan region from June to October, and especially from August to October, and monsoons in the Xishuangbanna region from February to June, occasionally damage vanilla plantations. It is therefore necessary to strengthen and maintain plantations to prevent damage by typhoons or monsoons.
Furthermore, it is necessary to replant where the plants have died or been destroyed by livestock or poultry, and so on. Measures should be taken to keep them away from plantations located near to dwellings.
Diseases
In different vanilla-growing regions in China, vanilla diseases, especially Fusarium root rot caused by F. oxysporum f. sp. vanillae (Tucker) Gordon has been a limiting factor to vanilla production. The integrated control measures for vanilla plantations in practice put prevention first, combined with treatment.
The measures recommended to prevent and counteract vanilla diseases are as follows:
• Avoid choosing low-lying and clay soil for growing vanilla plants, but choose gently sloping land that is well drained with a thick surface layer of humus.
• Use healthy seedlings for planting.
• Create a favorable environment for vanilla plants, especially better soil conditions by organic mulching in the rhizosphere.
• Do not trample on the planting belts when carrying out pollination or other operations.
• Regularly remove the disease-affected portions and apply necessary medicament treatments in emergency cases.
• Compartmentalize the plantation into different sections to prevent the disease spreading once it has occurred.
• Apply comprehensive measures, such as pruning and training plants, regulating shade, water drainage, and controlling flower numbers for pollination and so on, in order to rejuvenate vanilla plants and enhance their resistance to stresses and pathogens.
By applying the above measures, it is possible to reduce disease occurrence to an acceptable economic level and to guarantee long-term production.
Pests
Comparatively, insect pests do less damage to vanilla plants and are easier to prevent. Among these pests, coccidia must be promptly removed once they appear in the plantation, as their large-scale spread would destroy the vanilla plantation; it is hard to kill them since they are covered and protected by a waxy layer. Furthermore, terrestrial molluscs, snails and slugs, may cause certain damage to the tender parts of vanilla plants. Their population size can be efficiently controlled by attractant trapping and manual mass killing.
Harvesting
After planting, vanilla usually starts flowering in the third year. Vanilla plants growing in China bloom once a year, reaching the peak flowering stage in April, and are harvested during November to January of the following year. Depending on the degree of maturity of the beans, the right time for harvesting is when the beans turn a pale yellow color at their distal end. Harvesting earlier or later would have negative effects on the quality of cured beans.
Curing
The harvested green beans have no aroma or flavor; this will develop after curing.
Careful processing of beans will take 4–5 months depending on the climatic conditions. Various companies in China have developed different methods and capacities for processing vanilla beans. Although, different methods are used in different companies, they are all fairly similar.
The following takes the method employed in the former Yunnan Vanilla Company as an example to present an overview of the processing method in China, which consists of cleaning, killing, fermenting, slow drying and conditioning, grading and packaging.