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Cultural Practices

Tobacco growing has a long prestigious history in Mauritius. It is a valuable cash crop and generator of employment.

Tobacco is a very sensitive and demanding crop. Farming techniques based on sound and disciplined practices are the key to successful growing of high quality leaf tobacco.

The information provided will no doubt be a valuable guide and tool to stimulate general awareness, understanding and interest. Above all, it should ensure implementation by the farming community of these techniques with a view to enhancing yield, quality and hence farmer revenue.

Progress of the Industry will depend considerably on our ability to overcome the existing constraints and to be prepared to meet the challenges we may have to face in the future. The ease of adaptation to innovation in the ever-changing circumstances will test the strength of our commitment.

 

SEEDBED MANAGEMENT

The production of strong healthy seedlings is probably the most important single factor in successful tobacco production. It is often said "seedbeds are the foundation of the crop"

Site of Seedbeds

The site chosen for seedbeds should preferably be a soil which has been left fallow for some months (at least 2-3 months). The previous crop should not have been a member of the family Solanaceae as commonly cultivated solanaceous crops such as egg plant (brinjal), tomato, chillies are host plants for diseases and pest attacking tobacco. The site should have good surface and internal soil drainage and adequate sunshine. It must be near an adequate and reliable water supply and easily accessible for close supervision.

Seedbed Preparation

Timely preparation of seedbeds is very important. Early to mid-December for the first season crop and mid June for the 2nd season crop is recommended. The soil must be cleared of all weeds. Beds are then raised 10-15 cms (4 to 6 inches) above the soil level. The seedbeds are usually of 10m2 (100 square feet) in area. The width is 1 .2m (4 feet) and the length 8m (25 feet). The bed can be of any length but the width should not be more than 4 feet. Two beds, each 10m2 (100 square feet), will provide enough seedlings for 0.4 hectare (one arpent) of field plantation.

Sterilization of Beds

It is very important to sterilize seedbeds. When we say sterilization, we actually mean partial sterilization. This is most important and the aims are to control:    

  • Weeds, by killing seeds;    
  • Nematodes; and    
  • Disease organisms.

Metham - Na (trade name Vapam) is the chemical recommended. Vapam is diluted in water and applied as a drench. One litre of Unifume is diluted in two gallons of water and applied over one bed 10m2 or (100 square feet). The Vapam is then watered in by further application of four gallons of water. Once in contact with water, Unifume forms a toxic gas which is responsible for sterilizing the soil. The effectiveness of vapam is increased if the bed is covered with a plastic sheet for 3 to 4 days. The seedbed must be kept moist for ten days after treatment. Some two days prior to sowing, the bed may be forked gently using a small fork so that any residual gas may escape.


Seed is sown two weeks after treatment.


Fertilization of Seedbed

Organic manure (farmyard manure) should always be applied before sterilization of seedbed. Mineral fertilizer, if necessary is applied after sterilization just before sowing. Half a kilogram of 6: 18:24(s) may be applied over one bed of 10m2 (100 sq. ft.).


Sowing
The optimum seed rate appears to be one gram or 2 c.c per bed. The usual procedure is to mix the seed with dry, fine sand (about 200 grams) and the mixture is evenly broadcasted over the bed. Avoid sowing under windy conditions. The best time to sow is generally early in the morning.

Before sowing, Ridomil 25 WP or Dithane M-45 may be applied at the recommended rate.

The seedbed is watered immediately after sowing. It is vital to keep the bed moist for about two weeks. This is the most critical period. Half a day's delay in watering during hot weather can lead to serious loss of seedlings. During this period, the seedbed is watered three to four times daily. Early waterings should be frequent and light, becoming less frequent and heavier as the plants grow. It is important to keep the bed moist but not too wet as excess moisture encourages disease, particularly damping off. The frequency of watering will, of course, depend a lot on soil type and prevailing weather conditions.

Oversowing should be avoided as it favours development of disease such as Damping-off.

 

Cheese-cloth covers may be used to protect germinating seeds from strong sunlight, heavy rain and wind damage.

Pest and Disease Control

Two weeks after germination, seedlings should be sprayed with Cuprox at the rate of 2 grams per litre of water and a synthetic pyrethroid such as Decis or Cymbush at the recommended rate.

Spraying should be done every week.

Virus diseases, mainly tobacco mosaic virus, can be quite serious, but good field hygiene will limit infection.


Earth-balling

Some four to five weeks after sowing, when seedlings have reached a height of about 2-3 inches, they are ready for earthballing. A mixture consisting of 3 parts of well-rotten farmyard manure and one part of soil (both previously sterilized) brought to the right consistency by the addition of water is used.

Seedlings are carefully pulled from the seedbed and some of the above mixture is pressed by hand around the root system of each seedling. The earth-balled seedlings are adequately watered and are at first, protected from strong sunlight by the use of cheese-cloth covers. They are gradually exposed to the sun and watering is reduced.

It is important to select strong, healthy seedlings for transplanting. Seedlings are ready for transplanting some ten days after being earthballed.

CULTURAL PRACTICES/FIELD MANAGEMENT

Land Selection

Usually, land which has previously been under sugar cane is selected. Avoid land with poor drainage and land which has been under a solanaceous or leguminous crop.

Tobacco is grown in the districts of Black River, Pamplemousses, Riviere du Rempart and Flacq. It is generally grown on the soils known as Low Humic Latosols and Latosolic Reddish Prairie. Most of the second season crop is found on rented land from sugar estates or big planters. The best quality of tobacco together with good yields are only obtained when climatic conditions are such, as to ensure rapid and uninterrupted growth of the plant. The main requirements are a fairly high temperature together with an evenly distributed rainfall during the growing period, at the same time the rainfall should not be excessive. As rainfall in the tobacco producing districts is usually very unevenly distributed, irrigation is required in many areas, particularly the dry areas.

Land Preparation

Mechanical land preparation, if needed, should preferably be done a few weeks before planting. A light cultivation may then be necessary just before planting. On heavy soils, ridging will facilitate drainage and improve aeration.

Growing Seasons:

We have two growing seasons for Virginia flue-cured tobacco, the first season is from January to June and the second season from July to December. For Amarello air-cured tobacco. the growing season is from February to September.

Varieties

Recommended varieties are as follows:-

Virginia Flue-Cured tobacco: NC95, Speight G28, K326 and RG13
Air-Cured tobacco: Amarello Variety

This variety, originally introduced in 1962, is still the most popular variety. It is highly resistant to Bacterial Wilt and moderately resistant to Black Shank. Its Yield varies from 650 to 850 kg per arpent depending upon weather conditions and levels of crop management. Its quality is acceptable to the trade.

Variety
Speight G28


This variety was introduced in 1974. It has a fairly high resistance to Black Shank and a moderate resistance to Bacterial Wilt. Its yield potential is rather similar to NC95 but its quality appears to be slightly better.

Introduction and testing of new varieties of tobacco is a regular feature of the reseach work at the Richelieu Experimental Station. Some breeding work using the tissue culture technique is also envisaged.

Planting
An overcast sky and a moist soil are ideal conditions for transplanting. The spacing and fertilizer requirements are as follows:-

(a) Spacing
Distance between rows: 100 cms (3.3 feet) Distance between plants: 60 cms (2 feet)


This will give a plant population of about 6,600 plants per arpent or about 16,500 plants per hectare.


(b) Fertilizers

The amount of N,P and K fertilizers to be applied depends on a number of factors mainly soil and climate. Fertilizers generally recommended are as follows:-

1. For Virginia Flue-Cured:

Sulphate of Ammonia (21 %N) : 50- 75 Kg per arpent

or Calcium Ammonium Nitrate (26%N)

Simple Superphosphate (19% P2 AS) : 250 Kg per arpent

or Triple Superphosphate (45% P2 AS) : 100 Kg per arpent

Sulphate of Potash (50% K2 0) : 100-125 Kg per arpent

OR

The Special fertilizer 6: 18:24(s)+ 2MgO at the rate of 200-250 Kg per arpent, which is strongly recommended.

Chloride form of Potash should never be used.

2. For Amarello Air-Cured:

Sulphate of Ammonia : 150-200 Kg per arpent 

Simple Superphosphate : 250 Kg per arpent

Sulphate of Potash : 100-125 Kg per arpent

OR
The special fertilizer 6: 18:24(s)+ 2M gO at the rate of 300 Kg per arpent.
All fertilizers should preferably be applied at planting. Only fertilizers recommended by the Board should be used.

Time of Planting

The optimum time of planting for the first season Virginia flue-cured crop and of the Amarello crop appears to be the beginning of March and for the second season Virginia flue-cured crop the end of August. Late planted first season crop wiil not develop properly owing to decreasing temperature and daylength whilst late planted second season crop will be exposed to cyclonic weather starting in December.

Irrigation

Rainfall in the tobacco producing districts is generally very erratic. For the first season Virginia flue-cured crop, the rainfall often tends to be excessive. However for the second season Virginia flue-cured crop, irrigation is essential. The sprinkler irrigation system is commonly used.

After transplanting, depending upon weather conditions, half an inch of water may be applied daily for two to three days to obtain early and rapid establishment of the crop.

A uniform stand of strong, healthy plants is the basis for good yields. Later, the amount of irrigation water and the frequency of irrigation will depend upon a number of factors:

(a) Type of soil
(b) Stage of growth of the plant
(c) Climatic conditions

The water requirement is highest from the knee-high to the flowering stage of the crop. During the harvest period, irrigation may not be needed except in the case of extreme drought.

As a guide, the following irrigation schedules may be helpful:-

(a) For low Humic Latosols - (Deep Soils in Pamplemousses & Black River)

(i) Early stage of Crop - application of 1- 11/2 inches (3-4 cm)     every 10-12 days.

(ii) Knee-high to flowering stage - application of 1-11/2 inches (3-4 cm) every 7 - 10 days

(b) For Latosolic Reddish Prairie Soils - (Shallow Soils in Riviere du Rempart and on East Coast)

(i) Early stage - application of 1 inch (2.5 cm) every 7 days.

(ii) Knee-high to flowering stage - application of 11/2 inches (4cm) every 7-10 days.

In general, water available for irrigation in the tobacco producing districts is suitable quality wise; producers should, however, pay particular attention to water quality, e.g. in the use of effluents from sugar factories.

Pest and disease control

Proper control of pests and diseases is most important.

Cutworm may be an important pest at transplanting stage, particularly in humid regions. Sugarcane stumps and thrash tend to favour cutworm populations. Control measures recommended are:

(1) A synthetic pyrethroid such as Decis (0.8 c.c./litre) applied as a drench prior to planting.
(2) Dursban at the rate of 2-5 ml/lt.
(3) Removal of stumps and thrash from the field before planting.

The tobacco budworm (Heliothis sp.) is the main pest. Spraying with Methomyl (trade name Lannate) or a synthetic pyrethroid such as Decis or Cymbush at recommended rates at weekly interval will give effective control of this pest. It is however, recommended to use any two of the above pesticides alternately, that is, spraying with Lannate to be followed by spraying with Decis or Cymbush the following week.

Correct supervision during application of pesticide is needed.

Experiments and experience have shown that as far as pest or disease control is concerned, field spraying alone is not altogether effective unless strict field hygiene is practised.

It is imperative to use only pesticides recommended by the Board.

Leaf spots (e.g. Frog Eye) - Apply Dithane M-45 or Benlate at the recommended rate every 14 days. Emphasis is put on limited use of pesticides through appropriate cultural practices and strict field hygiene. In view of the increasing concern about the residual effect of dithiocarbamate fungicides i.e dithane M-45; Zineb and Metham-Na); use of alternative fungicides such as Ridomil 25 WP, Benlate & Basamid are now recommended.

Cultivation/Weeding

Land must be kept clean, specially in the early stages of plant growth. It is generally not necessary to weed more than two to three times. During weeding and cultivation, lower, senescent leaves of the plant may be removed and a light earthing-up may be done.

Trials on the chemical control of weeds are being conducted at Richelieu Experimental Station.

Topping

Topping means the removal of the flowerhead and the first few top leaves. The aim is to prevent the production of seed. Topping also leads to an increase in leaf area, leaf thickness and ripening is often hastened. Topping early and low is recommended for flue-cured tobacco as well as for Air-cured tobacco.

Topping should begin when approximately 10% of the plants are in flower. As flowering is not uniform, topping may have to be done twice or thrice in the same field. In general by low topping, about 20 leaves are left on the flue-cured plant and about 30 leaves on the air-cured.


Suckering

Suckering refers to the removal or control of suckers. After topping, side shoots or suckers develop rapidly. Suckers can be used as a safety valve for too much nitrogen and the frequency of suckering will thus depend on the rate of ripening and the rate of growth of the suckers. Generally suckers are removed at ten days intervals.

Chemical control of suckers is now recommended as it saves labour at the critical time of harvesting.

Tabamex applied at the recommended dilution and rate will give good control of suckers.

Harvesting

Harvesting of leaves is by priming, i.e. removal of leaves individually from bottom to top. Leaves should be harvested ripe.

Ripeness is often very difficult to assess and the producers should be prepared to begin reaping about the early bud stage, a week or so before topping. Harvest may then have to be done at weekly interval. It is important not to harvest unripe leaf, also leaves should not go overripe as this leads to a reduction in yield and quality. During harvest, steps should be taken to minimise physical damage to leaf; harvested leaves should not be exposed to the sun.

Harvested leaves should be tied on sticks as soon as possible and the sticks placed in the barn without undue delay. Close supervision is required during the whole process of harvesting and tying of leaf.

Tobacco leaf stitching machine may also be used in the preparation of leaves for curing. This operation minimises leaf manipulation and decreases labour requirements.

CURING

There must be sufficient accomodation to obtain best results from curing. The conventional barn is still widely used although a few producers are now using bulk curers. The barn should be carefully loaded, the sticks being evenly spaced about 9 inches (22cms) apart.

Curing is a continuous process but for the sake of convenience, the flue-curing process will be divided into three stages:-

(i) Colouring
(ii) Leaf Drying
(iii) Mid-rib Drying

Colouring

Colouring should begin at a temperature of 30�C (85�F) as soon as possible after the barn is filled. Top and bottom ventilators should normally be closed at the start of colouring. However, if the ambient conditions are wet, it is advisable to open slightly top and bottom vents.

The temperature of 30�C (85�F) should be maintained until a definite colour change is noted in the leaves on the bottom tier. At this stage, the temperature should be raised to 35�C and slight ventilation should be provided. Here. a hygrometer giving an indication of humidity inside the barn is essential.

A temperature of 35�C (95�F) is maintained until colouring is well advanced. Temperature should then be increased to 38�C (100�F) and remain there until colouring is complete. Only a trace of green should now remain in the mid-rib and main veins of the leaf. At the end of the colouring phase, the leaf will tend to show a wilting appearance.

Leaf Drying

When the leaf is fully coloured, the colour must be 'fixed' in order to obtain best quality leaf. Ventilators should be adjusted so that the maximum amount of air enters the barn and passes through the tobacco and temperature must be increased in steps to create a draught through the barn.

The rate at which temperature should be increased depends on the type of tobacco being cured. With slow ripening tobacco, the suggested rate of increase is 3�C (5�F) every six hours and with fast ripening tobacco. 3�C (5�F) every four hours. However, if ventilation through the barn is adequate, it is possible to raise temperature from 38�C to 70�C (100�F to 160�F) more rapidly and at a constant rate.

The wet bulb temperafure should be maintained at about 35�C (95�F) until the lamina of the leaf is dry
through most of the barn. An increase of wet bulb temperature to between 35�C (95�F) and 38�C (100�F) indicates that ventilation is becoming inadequate to cope with moisture removal. If ventilation cannot be increased further, the dry bulb temperature should be held constant for some time until the wet bulb temperature drops.

Mid-rib Drying

The mid rib is finally dried out by maintaining temperatures at 70�C (160�F) and progressively reducing ventilation in order to save on fuel.

A few common curing faults are as follows:-
(a) Barn Rot - Indicates inadequate ventilation during colouring.
(b) Sponge or Browning - indicates inadequate ventilation during drying.
(c) Perished and over-coloured leaf - shows that the drying rate was too slow and the leaf not 'fixed' soon enough.

Attention should be paid to fuel conservation by having a tight and well insulated barn.

The above is given as a guideline. The whole process may take 5-6 days. Producers should contact the Extension Staff of the Tobacco Board for more information.

Air-Curing

There must be adequate shed space for curing the crop. For optimum curing, the relative humidity should average 65-70%. Adequate ventilation must be provided at all stages of the curing process. Air-curing takes 2 to 3 weeks depending upon weather conditions. The cure is complete when the mid-ribs are dry.

Conditioning of Cured Leaf

Once the cure is complete, the barn should be cooled as quickly as possible. When the leaf is soft enough to be handled, the barn can be unloaded. Over-conditioning of leaf should be avoided.

Grading

The new grading system involving plant is now being recommended for flue-cured tobacco.

Plant position grading is the process of grouping cured leaves into uniform lots according to plant position (reaping), colour and degree of damage or spotting.

 

Plant position grading is the process of grouping cured leaves into uniform lots according to plant position (reaping), colour and degree of damage or spotting.

 


 

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