The major means of spread of the virus is through the use of infected stem cuttings. Insects may also play an important role in the transmission and spread of the disease in nature.
Management of viral diseases
• Use of virus-free planting material is the primary requirement to check spread of the virus. Apparently healthy looking plant should not be used for any new planting as this would carry the virus which eventually would show the disease symptoms after planting. If tissue culture raised plants are used, it is important to check for the presence of virus in the mother plant. If the mother plant is infected with the virus, the plantlets derived form this will also carry the virus thus contributing to its spread.
• Regular inspection and removal of infected plants and replanting with healthy plants
• Weed and crop hosts (especially pea, pumpkin and watermelon and other hosts) which might act, as reservoir for the virus also needs to be removed. The removed plants may be burnt or buried deep in the soil.
• Insects such as aphids act as vectors for the different viruses.
These insects whenever noticed on vanilla plants may be controlled with insecticide spray. Insecticides like dimethoate or monocrotophos @ 0.05% can control aphids, and other sucking insects.
• Movement of planting materials from infected regions to disease free regions should be avoided.
Insect pests
Leaf feeding beetles and caterpillars
Very few serious insect pests have been recorded on vanilla in India. A few species of leaf feeding caterpillars and beetles feed on leaves and tender stems. Leaf feeding caterpillars and beetles can be controlled by spraying quinalphos 0.05%.
Sucking bug
Adults and nymphs of the sucking bug Halyomorpha sp. infest tender shoot tips and emerging inflorescences resulting in their drying and rotting. Spraying quinalphos (0.05% each) on tender shot tips and emerging intiorescences is effective for management of the pest.
Snails
Snails and slugs feed and damage tender shoot lips and leaves especially in moist and shaded areas in the plantations. I land-picking and poison baiting helps in preventing the pest
Harvesting
The beans or pods are ready for harvest 6 -9 months after flowering. The beans can be considered as mature when they change from green to pale yellow. At this time, the pods may be 12-25 cm long. It is essential to harvest the pods at the right stage, as immature pods produce an inferior product and over-mature pods split during curing. The right picking stage is when the distal end of the pod turns yellow and fine yellow streaks appear on the pods. Daily picking of mature pods is essential. The pods can be harvested by cutting with a knife.
A good vanillery yields 300-600 kg of cured beans per hectare per year. About 6 kg of green pods produce 1 kg of cured beans. The yield of the vine declines after 12-14 years.
Curing
Green vanilla beans (pods) contain little vanillin and is odourless and flavourless. It is during curing that the beans undergo enzymatic reaction responsible for the characteristic aroma and flavour of vanilla. Curing should preferably begin immediately after har-vesting, but the beans can be stored for 3-5 days. There are different methods of curing but they all consist of more or less four stages.
1. Killing the beans to allow the onset of enzymatic action.
2. Sweating, for raising the temperature to promote enzymatic action and enhance rapid drying for preventing fermentation.
3. Slow drying for development of fragrance.
4. Conditioning the product by storing for a few months in closed boxes.
The important methods of curing vanilla are Mexican Process, Bourbon Process, Peruvian Process and Guiana Process. In the Mexican process, killing is done by exposing the harvested beans directly to the sun for about 5 hours, which produces the optimum percentage of vanillin content. In Bourbon process, bamboo baskets with the beans are immersed in hot water (63-65°C) for 3 minutes. After rapidly draining the water when the beans are still hot, they are kept in wooden boxes lined with blankets. The beans acquire chocolate brown colour the following day. They are then spread in the sun on dark coloured cotton covers for 3-4 hours and later rolled up to retain the heat and stored in wooden boxes. This process is repeated for 6 to 8 days, during which the beans lose some weight and become very supple. Later the beans are dried by spreading them out in wooden trays under shade in an airy location. The duration of drying varies according to the size of the beans and usually lasts for 15-20 days. Properly dried beans are kept in closed containers where the fragrance is fully developed. Finally they are graded according to size and kept in iron boxes lined with paraffin paper. Care should be taken in the early stages of drying to keep the beans straight, because curved beans are considered as inferior in quality. When properly cured and sun dried the vanilla beans will be almost black and supple enough to be bent without breaking and vanillin crystallizes over the beans. Properly cured vanilla beans contain about 2.5% vanillin.
Vanillism
Vanillism, an occupation hazard is caused by poisoning due to vanillin. Vanillism is characterized by headache, gastric trouble and rashes over the body. The sap of vanilla plant can also cause severe allergic reactions such as itching, skin rashes and inflammation.