Section II - Nutmeg cultivation
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6. Weed control
7. Pest, diseases and their control
8. Cultivation practice
Two methods have been predominantly used for propagating nutmeg plants in Grenada. There were the seedling method and the vegetative method.
1.1 The Seedling Method
- From Volunteer Plants
Traditionally, small farmers have used "volunteer plants" as seedlings for planting. These seedlings have their origin from fallen seeds that have germinated and grown in and around the parent plant. The farmers may use seedlings at two stages of development, the young undeclared plants, plants which have not flowered, or the more mature declared plants, which have flowered and thus the sex could be identified. In the latter instance plants that produced female flowers and then fruits will be selected.
- From Government Agricultural Stations
Nutmegs are usually propagated by fresh seeds with their testa still attached. Seeds where the kernel rattle in the shell and old seeds will not germinate. In shaded nurseries the selected seeds are sown 2.5 - 5 cm deep and 30 cm apart in boxes or well prepared moistened nursery beds. Germination takes about one month or more. After two to three months the plants average about 15 cm in height. They are then transferred to baskets or plastic perforated bags. At six months they may be transplanted to the field but usually they are left for up to twelve or twenty four months (photograph 12a).
As regards seed germination it has been observed that there was a rapid decline in percentage germination if seeds are planted later than three days after harvest. Removal or scarring of the shell facilitated germination. Also there was some connection between monthly yield by the parent tree and the level of germination. Higher germination percentages were evident for seeds taken from plants with high monthly yields.
1.2 The Vegetative Method
Following the ravishes of hurricane lanes in 1955, which completely or partially destroyed most of the nutmeg tree population nation wide, investigation into the vegetative propagation of nutmeg was initiated. Two methods emerged and were established in commercial approach-grafting and marcotting. (Nicols and Cruickshank, 1964; Cruickshank, 1973). The later, however, became the preferred method in Grenada. In approach-grafting for seedlings, with the diameter of a pencil (0.5 cm) or lime larger around the collar region and about 45 cm high as grown or transplanted into perforated plastic bags, the potting mixture is moistened and the potted plant enclosed in a larger unperforated plastic bag. This seedling (stock) is approached - grafted to a twig of similar thickness "scion" on a female tree. The procedure was the removal of very thin sections of bark about 28 cm long, on both stock and scion. These were securely tied and bound together with clear budding tape. After about four months the grafts unite and the scion is severed below the union. The plants are repotted in a rich potting mixture (soil, compost, river sand, in the proportion 5:3:2) and placed in closed concrete hardening bins and hardened off by gradually lifting the bin covers until they are fully exposed. Plants are then stored under 70% shade before field planting.
In marcotting or air-layering, vigorous healthy branches, 1.2-1.5 cm in diameter are chosen from selected female trees. The branch is split in the middle longitudinally for 5 cm at a distance of 90 cm from the terminal growth. A bamboo or wooden splint is placed on the back of the split and tied firmly at both ends with plastic tape, string not used to avoid rotting. A portion of the split branch 6-12 mm long is then removed on the lower side of the split with secateurs. The cut end is lifted and a splint of hard wood is inserted to keep the split open. The section is then dusted with rooting stimulant such as seradix L15. Moist peat moss, sawdust or coconut coir dust are applied around the split, extending above and below the incision for 5 and 10 cm respectively. Such a medium was kept in place by polyethene sheeting, tied around the branch and secured with plastic tape. Roots occur after 4 - 18 months. Once rooting is adequate the plant is severed from the tree and potted, after removal of polyethene sheeting. The plants are kept in closed concrete bins covered with clear plastic and watered thrice daily for a period of 6 8 weeks. The plants are then hardened off by lifting the bin covers until they are fully exposed. This is done for a period of two to three months. The plants are then stored under 70% shade for a further 8-10 weeks before planting in the field.
Despite the perceived negative attitude of some farmers to marcots (Aegis, 1975) it is significant to note, that with the increase efficiency of rooting in marcots form 30 to 43%, such planting material eventually contributed significantly in the recovery of nutmeg tree population after Janet. By 1973 the Ministry of Agriculture had reported that about 37 thousand marcots were used to cover an area of about 1000 acres (400 ha).
Further, it must be noted that in 1959 and later, nutmeg seeds were imported from Malaysia and seedlings from this stock have been planted in many nutmeg fields. Although on an average the nut and mace of the Malayan fruits tend to be smaller than the regular nutmeg plants grown in Grenada, very interestingly in the Malayan population there is a very small proportion of unisexual male trees when propagated from seedlings. There is a small Malayan tree grove at the Government Agricultural Station in Mirabeau.
The common practice before planting young nutmeg trees was to preestablish shade, windbreak and soil conservation programmes. Banana was commonly selected as the crop of choice to provide temporary shade for young nutmeg plants. However, nutmegs have also been interplanted with cocoa (photograph 12b).
For marcotted material, the holes are dug just about 60 cm² and the soil mixed well with rotted or well composted manure. The young plants are set in the holes and staked with wooden stakes. Plants are spaced on an average 9 m apart. Shade plants are usually gradually reduced from after the second year and by the seventh year may be completely removed. Marcots may begin flowering as early as three to four years.
When the planting material is undeclared seedlings the common practice is to plant three seedlings at a planting site, 60 cm apart in the form of an equilateral triangle. Shade crops are used as in the case of marcots. The shade requirements for transplants are:
|Up to 2 years||50% overhead shade plus ground shade|
|2 to 4 years||40% overhead shade plus ground shade|
|4 to 5 years||30% overhead shade plus ground shade|
|6 years||15% overhead shade plus ground shade|
|7 years and older||No shade|
Shade should be reduced gradually so as to minimize shock. At the first flowering usually at 4-7 years, the male plants are destroyed leaving one female per planting site. Some farmers may leave a few male trees in the field to encourage cross-pollination. This practice is declining. However, no studies have been reported that show the correlation between presence of male flowering trees and the quantity and quality of fruits and seeds that are produced by the female plant.
For the establishment of larger declared seedlings, the practice is to prepare the planting hole well in advance. The hole size will be proportional to the size of plant and the soil mass that will be removed with it for transplanting.
Once the plant is selected, the soil around the plant is cut in stages, one side at a time to a level just below the root and a distance from the stem of about 60-90 cm. The staged cutting afford the roots time to heal. Usually, on a wet day the young plant is removed with as much soil as possible, carefully transferred to the prepared hole covered with manured mixed soil and securely staked. Such plants will just continue flowering and fruiting.
Usually trees come into full bearing at about 20-25 years and continue at that level for another 30 40 years. It has been reported that trees above this age start registering progressive productivity drops.
The earlier trees from marcotting and the introduced Malayan plants are just now over 30 years so that their productivity levels at older ages is not yet known. Trees from Marcots always tend to show more lateral spread than increase in height, a condition that necessitates pruning.
The population of nutmeg trees in Grenada is estimated at about 400 450 thousand made up of a mixture of trees from the original Banda stock, the more recently introduced Malayan extract with plants propagated from seedlings, marcotting or approach grafting. Although the majority of trees may be under 40 years, there are some 100 years and over that are still productive.
Pruning is recognized and considered a good practice to maintain or increase flower, fruit and seed production. This envolves the removal of water shoots and upright branches within the plant, dead wood, cutting back of lower branches and the defining of an individual plant so that it does not become shaded by neighboring plants in a canopy.
Photo. 12a. Two year
old nutmeg seedlings at Ashenden Propagation Station
Photo. 12b. Six year old nutmeg seedling interplanted with banana and cocoa
Photo. 13. Nutmeg leaves with leaf shot
It has been observed that farmers tend to prune more completely and regularly when the financial returns for nutmeg and mace are high. At other times pruning is neglected and certain farmers advance the argument, more branches more fruits.
Young nutmeg trees (volunteers) were often cut and used for making swizzle sticks. This was so because of the morphology of the stem and branches; whorled branches and a periodic stem growth.
It is not the practice to fertilize nutmeg plants in Grenada. However, since nutmeg plants are usually intercropped with banana or cocoa it is said that nutmeg trees inherit the spill off.
There exists no tested trial information on fertilizer use in nutmegs. Some trials were planned, and even attempted but the results were inconclusive (Cruickshank,1973). Again most farmers attitude is that the trees are doing well in production without fertilizer, so applications may only exhaust the trees.
According to Buckmire (1992) the suggested regime of fertilizer application is as shown below, this is rarely followed as most farmers avoid the use of fertilizer.
|Year 1||0.5 kg sulphate of ammonia or calcium ammonium nitrate at the beginning of the rainy season.|
|Years 2, 3 and 4||1 kg 16:16:16(NPK) in two applications the first early in the rainy season and the second Oct./Nov.|
|Years 5 and 6||2 kg 16:16: 15 as above.|
|Year 7 and older||2.25 kg 16:16:16 as above and then increasing by0.5 kg per annum to a maximum of 4.5 kg.|
The nutmeg plant requires well drained soil with good water retention properties but no water logging. Most nutmegs are grown on hillsides and in most nutmeg growing areas the soils are either Capitol or Belmont Clay loam. Both of these soils are moderate to well drained yet affording good water retention. Irrigation is therefore not practiced in nutmeg fields. However, the fields are usually contoured with drains to afford good run off. If newly planted trees encountered a period of dry spell then such plants are watered periodically.
6. Weed control
This is dependent on the age of plant and its final configuration as related to other plants. For young plants efforts are made to prevent their strangulation by vines, thus cleaning may be as much as four times yearly.
As the plant ages the canopy thickens and this assist in weed control underneath. In isolated trees the weeds underneath are controlled to facilitate harvesting of fruits and seeds. Weed control is usually by slashing.
7. Pest, diseases and their control
According to Cruickshank (1973), the nutmeg tree has no serious insect pest in Grenada and just a few diseases of varying significance. Farmers have not reported about pest and diseases in their nutmeg plants. However, the listed problems are:
|1. Mace scab||- a white callous like outgrowth mace suggested to be calcium oxalate by Pierre (1970).|
|2. Greasy spot or||- dark brown leaf greasy lesions on leaf shot the leaf blade associated with the saprophytic fungi like Nigrospora, Botryodiplodia and Collectotrichum (photograph 13).|
|3. Thread Blight||- caused by the fungus (Corticium spp.)|
|4. Wilt(nutmeg decline)||- Most high profile disease in nutmeg locally.|
7.1 Nutmeg wilt
This is the most important disease in nutmeg in Grenada. Although this disease is associated with several fungi, Rosellinia sp. has featured most in the association but its causal role in the disease has not been demonstrated (Muller et al., 1990). Thus the cause of nutmeg wilt is still unknown. It is generally assumed that the agent is a pathogen but there may well be other predisposing factors. The symptom associated with nutmeg wilt is the gradual wilting of a plant and dieback of the roots. This is accompanied by excessive leaf and fruit drop with eventual tree death. There is no definite method for the control of this disease (photographs 14a, b, c, and d).
8. Cultivation practice
Nutmeg is seen as a crop just to be harvested and traditionally and continuing into the present, not many farmers carry out any routine good cultivation practices. The plants are given some care when young but are basically neglected on maturity.
The attention given is often directly related to the price being received by farmers for their nutmeg products.
Photo. 14a. Nutmeg wilt - early
symptoms of slow decline
Photo. 14b. Nutmeg wilt - sudden wilt
Photo. 14c. Nutmeg wilt - advance symptoms, total die back
Photo. 14d. Nutmeg wilt - dead standing tree trunks
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